front-end design for a multi-mission, multi-standard satellite … · 2011. 1. 12. · band at...

Diploma Thesis

Front-End Design

for a Multi-Mission, Multi-Standard

Satellite Ground Station

under the supervision of

Dipl.-Ing. Michael Fischer

and

Univ.Prof.Dr. Arpad L. Scholtz

E389

Institute of Communications and Radio-Frequency Engineering

Vienna University of Technology

Electrical Engineering

by

Adria Ainhoa Solana Esteban

0927152

Karolinengasse 6, 1040 Wien

DNI: 24392892-N

Vienna, July 2010

Acknowledgements

First of all, I would like to thank my supervisors, Dipl.-Ing. Michael Fischerfor his support along these months, his invaluable help at all times, and for hisendless patience and optimism, and Univ. Prof. Dr. Arpad L. Scholtz, who wasalways kindly willing to help me in any kind of problem that came up, and wasalways eager to share his knowledge and curiosity in life with me, and managedto make my stay much more enriching and fulfilling.Moreover, I would like to thank Jonathan Ronquillo for his relentless help andsupport when I most needed, for caring about me and for making my days muchmore pleasant.I would also like to thank Peter Witschel for always finding time to help me, forcaring and for doing it with a big smile.Furthermore, I would like to thank other friends, like Rocío Morales who patientlyhad to listen to me talking about things she couldn’t understand but alwaysmanaged to cheer me up, Edu Tormo, for supporting me every day from thedistance and believing in me, and Sara Martínez, who had always the perfectwords to cheer me up and who I’m missing so much since she left.I would like to thank specially René Sapetschnig for being there for me everyday, for taking care of me, for supporting me, for making my days, for puttingup with all my complaints and for being so patient.Finally, but definitely not less important, I would like to thank my family. With-out my mother, this experience would have never been possible. I would liketo thank her for her caring, her strength of spirit and support, not only thesemonths, but my whole life, which has made me the way I am. Also, I would liketo thank my aunt Olga for worrying, caring and asking about me every day.Thank you all!

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Abstract

It can be said that satellites are a proof of technical advance. Their use inphysics, astrophysics, communications, among others, have turned them into areliable and unconditional everyday tool. Moreover, nowadays, satellite commu-nications do not serve mere commercial services but also educational scientificradio research. This is feasible due to the possibility of building low cost space-crafts and earth stations for LEO, allowing, for instance, universities to carry outeducational research.

Specifically, Vienna University of Technology, Institute of Communications andRadio-Frequency Engineering is currently building a ground station that will com-municate with satellites in LEO at scientific and amateur radio S-band (2.00-2.45 GHz), as well as in UHF (435-438 MHz) and VHF (144-146 MHz) bands.The mission and projects supported in the first step by the ground station areof special scientific interest in the field of asteroseismology, physics and commu-nications, and highlight the countless possiblities that LEO communications canoffer.

In this thesis, I describe a radio-frequency S-band front-end design and com-ponent selection of a ground station supporting BRITE Constellation mission,GENSO project, COROT satellite and MOST project. The ground station is de-signed to be flexible and open for future add-ons or modifications. Link budgetsand propagation losses are carefully calculated in this thesis, predicting excep-tional performance in the uplink and downlink of the institute’s ground station.

iii

Resumen

Los satélites son una prueba más del avance tecnológico actual. Su uso en loscampos de la física, la astrofísica y las comunicaciones, entre otros, los ha conver-tido en utensilios fiables, a la vez que imprescindibles en el día a día. Asímismo,en la actualidad, las comunicaciones por satélite no sirven únicamente servicioscomerciales, sino que también son aprovechadas por los usuarios amateur (afi-cionados) y universidades. Este hecho es posible gracias a la opción de construirsatélites de órbita baja y estaciones terrenas de bajo coste, permitiendo, porejemplo, que las universidades tengan acceso a este terreno y puedan llevar acabo investigaciones con propósitos educacionales.

En concreto, el Instituto de Comunicaciones e Ingeniería de Radiofrecuencia,de la Universidad de Tecnología de Viena, está construyendo en el edificio dela facultad de Ingeniería Eléctrica una estación terrena que se comunicará consatélites de órbita baja en la banda S (2.00-2.45 GHz), tanto en la subbanda cien-tífica como en la subbanda amateur, así como en las bandas UHF (435-438 MHz)y VHF (144-146 MHz). Las misiones espaciales soportadas por esta estación ter-rena, son de especial interés científico en los campos de la asteroseismología, lafísica y las comunicaciones, y ponen de manifiesto las numerosas posibilidadesque ofrecen las comunicaciones mediante satélites en órbita baja.

Esta tésis, como parte del proyecto descrito anteriormente llevado a cabo porla Universidad de Viena, consiste en el diseño de la parte de radiofrecuenciaen banda S y selección final de los componentes de una estación terrena quese comunicará con los satélites pertenecientes a las misiones de la constelaciónBRITE, el proyecto GENSO, el satélite COROT, así y como con el proyectoMOST. La estación terrena ha sido diseñada de manera que sea flexible y abiertaa futuras modificaciones y características adicionales. Los balances de potenciay las pérdidas de propagación han sido calculados cuidadosamente en esta tésis,prediciendo un comportamiento excepcional tanto en enlaces de subida como debajada.

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Contents

1 Introduction 1

2 The Project MOST 22.1 MOST Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 MOST Satellite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.3 MOST Orbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.4 MOST Communications . . . . . . . . . . . . . . . . . . . . . . . 3

3 The COROT Satellite 43.1 COROT Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . 43.2 COROT Satellite . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.3 COROT Orbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.4 COROT Communications . . . . . . . . . . . . . . . . . . . . . . 6

4 The BRITE Constellation Mission 74.1 BRITE Mission Objectives . . . . . . . . . . . . . . . . . . . . . . 74.2 BRITE Constellation Satellites . . . . . . . . . . . . . . . . . . . 94.3 BRITE Orbits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.4 BRITE Communications . . . . . . . . . . . . . . . . . . . . . . 124.5 Summary of BRITE . . . . . . . . . . . . . . . . . . . . . . . . . 13

5 The GENSO Project 155.1 GENSO Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . 155.2 Typical Educational Satellite Features . . . . . . . . . . . . . . . 185.3 Educational Satellites Orbit . . . . . . . . . . . . . . . . . . . . . 185.4 Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

6 Concept of a Multi-Mission Ground Station 216.1 General Concept of a Ground Station . . . . . . . . . . . . . . . . 216.2 Frequency Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256.3 Block Diagram of the Ground Station . . . . . . . . . . . . . . . . 26

7 Building Blocks Analysis and Selection 297.1 Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297.2 Feed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317.3 Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317.4 Duplex Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

v

Contents

7.5 Low Noise Amplifiers (LNAs) . . . . . . . . . . . . . . . . . . . . 337.6 Bandpass Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . 347.7 High Power Amplifiers (HPAs) . . . . . . . . . . . . . . . . . . . . 347.8 Polarization Selectors and Polarization Recovery Units . . . . . . 357.9 Upconverters and Downconverters . . . . . . . . . . . . . . . . . . 357.10 Modulators and Demodulators . . . . . . . . . . . . . . . . . . . . 367.11 Transceivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377.12 Terminal Node Controllers (TNCs) . . . . . . . . . . . . . . . . . 377.13 Cables and Waveguides . . . . . . . . . . . . . . . . . . . . . . . . 377.14 Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

8 Propagation Losses 398.1 Propagation Effects Classification . . . . . . . . . . . . . . . . . . 398.2 Propagation Effects at S-Band . . . . . . . . . . . . . . . . . . . . 40

8.2.1 Ionospheric Effects . . . . . . . . . . . . . . . . . . . . . . 418.2.2 Tropospheric Effects . . . . . . . . . . . . . . . . . . . . . 458.2.3 Local Effects . . . . . . . . . . . . . . . . . . . . . . . . . 478.2.4 Free Space Path Loss . . . . . . . . . . . . . . . . . . . . . 47

8.3 Cases Under Study . . . . . . . . . . . . . . . . . . . . . . . . . . 488.4 The BRITE Constellation Propagation Losses . . . . . . . . . . . 488.5 The GENSO Project Propagation Losses . . . . . . . . . . . . . . 498.6 The COROT Satellite Propagation Losses . . . . . . . . . . . . . 518.7 The MOST Project Propagation Losses . . . . . . . . . . . . . . . 51

9 Link Budgets 529.1 Link Budget Calculation . . . . . . . . . . . . . . . . . . . . . . . 52

9.1.1 Uplink Budget . . . . . . . . . . . . . . . . . . . . . . . . 529.1.2 Downlink Budget . . . . . . . . . . . . . . . . . . . . . . . 55

9.2 The BRITE Constellation Link Budget . . . . . . . . . . . . . . . 599.3 The GENSO Project Link Budget . . . . . . . . . . . . . . . . . . 599.4 The COROT Satellite Link Budget . . . . . . . . . . . . . . . . . 599.5 The MOST Project Link Budget . . . . . . . . . . . . . . . . . . 599.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689.7 Intermodulation and Interference . . . . . . . . . . . . . . . . . . 68

10 Summary 69

Bibliography A.1

List of Abbreviations B.1

List of Figures C.1

List of Tables D.1

vi

Contents

A Beam Spreading Loss using the ITU Model Ap.1

B Refraction and Fading using the ITU Model Ap.2

C Focusing and Defocusing using the ITU Model Ap.6

D Gaseous Absorption using the ITU Model Ap.7

E Rain Attenuation using the ITU Model Ap.11

vii

Chapter 1

Introduction

Vienna University of Technology has previous experience building successfulground stations, such as the station for MOST located at the Institute of As-tronomy of the University of Vienna [?]. This time, the Institute of Commu-nications and Radio-Frequency Engineering of Viena University of Technologyis determined to have success in a more difficult challenge: building a groundstation that will, not only support MOST, but it will also be capable of holdingcommunications with the COROT satellite, along with the BRITE Constella-tion satellites. Moreover, the ground station will be part of the GENSO project,allowing communications with all satellites operating in the amateur radio S-Band at 2400-2450 MHz as well as the UHF and VHF amateur radio bands, at435-438 MHz and 144-146 MHz, respectively.

This thesis will deal with the design of the Radio Frequency (RF) S-Bandfront-end of the ground station. In Chapters 2 to 5 the different missions andprojects that will be supported by the earth station will be explained in detail.Their aim, structure, operating frequencies, data transfer rates and orbits will bedescribed. Chapter 6 will deal with the general concept of the ground station,showing the final block diagram of the design and the frequency plan. In thedesign of an earth station, each stage of the design has to be carefully carriedout, as every element can affect seriously the whole system. In Chapter 7 eachcomponent will be analysed and justified, deciding which of them are critical tothe design. Finally, actual components will be selected in order to accomplishthe desired task.

The second part of the thesis, Chapters 8 and 9 , will analyse the groundstation’s theoretical performance by means of calculating the propagation lossesand the link budgets for different settings. Calculations will be carried out fordifferent elevation angles and also for different frequencies and satellite altitudes.

Nevertheless, apart from expecting good results, it should be taken into accountthat this station is designed so that it remains flexible, allowing communicationswith new satellites to be easily arranged just by incorporating new pipelines tothe existing system.

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Chapter 2

The Project MOST

2.1 MOST Objectives

The project Microvariability and Oscillations of STars (MOST) is a microsatellitespace telescope mission, managed by the Canadian Space Agency in cooperationwith the Institute of Astronomy of the University of Vienna and the Institute ofCommunications and Radio-Frequency Engineering of the Vienna University ofTechnology. The mission of the MOST satellite is to monitor the variations in thestars’ light by observing them for a long period of time (up to 60 days), in contrastwith other space telescopes, which though larger, cannot afford remaining focusedon a single star for such long periods due to the demand for their resources. TheMOST satellite is the first spacecraft dedicated to the study of asteroseismology.The main goals of the mission are to find out the limit age of nearby stars (thatmay lead to an approximation of the age of the Universe), as well as the searchfor possible exoplanets [1].

In the past years, the telescope has led to multiple discoveries, as, for instance,the finding of a new class of variable star: the slowly pulsating B supergiant, orthe detection of abnormal oscillations in certain stars [2],[3].

2.2 MOST Satellite

The satellite is only 65 cm × 65 cm × 30 cm large and weighs less than 60 kg.Despite its small size (see Figure 2.1), it has a small 15 cm aperture high precisionphotometric optical telescope [1] powered by solar panels and steered by a systemof wheels and magnetotorquers which allows the telescope to point, within 10arcseconds of the desired target, 99% of the observation time [3].

2.3 MOST Orbit

The MOST satellite has a polar sun-synchronous Low Earth Orbit (LEO) ofabout 830 km high and with a period of roughly 100 minutes. From that orbit,the front side of the satellite will have a continuous viewing zone in which the

2

2.4 MOST Communications

Figure 2.1: The MOST Satellite, [2]

target star will be visible for up to 60 days, and the back side will point to theSun [3],[1].

2.4 MOST Communications

There are already three ground stations working with the satellite, two in Canada(Vancouver and Toronto), and one in Austria (Vienna), sited in the Institute ofAstronomy of the Vienna University but property of the Institute of Commu-nications and Radio-Frequency Engineering of Vienna University of Technology,that take turns in communicating with the satellite due to their location.

However, although somehow redundant, our new ground station will also sup-port MOST, as it was not necessary to add many elements to the ground stationin order to be able to support this mission, and, what is more, it may serve as aback-up station for MOST.

Uplink and downlink communications are held at S-band, see Table 2.1, withuplink and downlink data rates of 9.6 kBit/s and 38.4 kBit/s, respectively. More-over, the MOST satellite is available up to 40 minutes per day, per ground station[3],[1].

Table 2.1: Frequency and data rates of the MOST satellite.

Uplink DownlinkFrequency (GHz) 2.055 2.232Data Rate (kBit/s) 9.6 38.4

3

Chapter 3

The COROT Satellite

3.1 COROT Objectives

COnvection ROtation and planetary Transits (COROT) is a mission led by thefrench national agency, Centre National d’Études Spatiales (CNES), along withmany other collaborators, such as the European Space Agency (ESA) [4]. Thesatellite was launched on the 27th December 2006, and it will remain operationalfor at least 2 more years, mostly because it has been, so far, tremendously suc-cessful in its assignments [4, 5].

COROT’s main tasks are:

• To search for exoplanets (precisely rocky planets larger than or equal toEarth, with short orbit periods, that are outside our solar system) usingthe method of planetary transits. This method consists of detecting planetsby detecting the drop, due to the light blocking, in the star’s brightness (thestar that the target planet orbits around) as the planet passes in front ofit. This method reveals both period and size of the exoplanets discovered[4, 5].

• To study the star’s interior by means of asteroseismology. The ripplesobserved on the surface of stars due to acoustic waves generated in theirinterior, alter their brightness and allow astronomers to calculate the star’sprecise mass, age and chemical composition [4].

In order not to be blinded by the Sun, as the Sun gets closer to the satellite’sorbit plane, the spacecraft rotates 180 and starts observing the opposite region.This happens twice per year. Therefore, the year is divided into two six-monthperiods of observation (by convention, summer and winter). Every 150 days,COROT will move to a new field and begin observing again [5, 4].

COROT will observe simultaneously up to 10 stars with magnitudes between6 and 9 [5] for the asteroseismology mission, and about 12000 less bright stars(magnitudes between 11 and 16) for the exoplanet search mission.

4

3.2 COROT Satellite

3.2 COROT Satellite

The COROT satellite is composed of a platform (PROTEUS Series) designed forsatellites that operate in LEO, and a payload which is made up of a telescope,two cameras – one for each of the two mission objectives (exoplanet search andasteroseimology), and on-board computer processors (see Figure 3.1). The te-lescope’s field of view is a square of 2.8 × 2.8, half used for asteroseismologyand half used in the detection of exoplanets. A prism will be used in order toseparate colours, allowing scientists to study stellar activity during a transit of aplanet. Both goals require the camera to be accurate in order to notice changesin a star’s light of one part in one hundred thousand. Consequently, an externalpanel or shield is placed around the telescope which prevents light pollution fromaffecting the telescope [4, 5].From the satellite’s point of view, the Sun will rotate 1 every day. To guaranteeenough power, the solar wing panels will rotate every 14 days [5].

Table 3.1 presents a summary of the main characteristics of the COROT sate-llite [5].

Figure 3.1: COROT Satellite. [5]

3.3 COROT Orbit

The COROT satellite describes a polar inertial circular orbit with 90 inclinationat an altitude of 896 km [5]. If placed at a higher altitude, the satellite would

5

3.4 COROT Communications

Table 3.1: Summary of the main characteristics of the COROT satellite.

Satellite Specification ValueMass 630 kgPayload Mass 300 kgLength 4100 mmDiameter 1984 mmPower 530 WPointing accuracy 0.5 arcsec

suffer from the solar radiation, and, if placed lower, the instruments would sufferfrom the reflection of the solar light on the Earth. Moreover, by means of havinga polar orbit, the orbit plane will keep a constant position with respect to thetarget stars.

3.4 COROT Communications

Several ground stations are distributed in different geographical places aroundthe world. Some of them with an specific task to carry out, and others just assecondary stations. For instance, the MOST ground station in Vienna acts as asecondary station for COROT.

COROT will only have a downlink in Vienna, at about 2.3 GHz. Both, RightHand Circular Polarization (RHCP) and Left Hand Circular Polarization (LHCP)are available, and the modulation used is Quadrature Phase Shift Keying (QPSK).High data rates, close to 1 Mbit/s, are feasible.

6

Chapter 4

The BRITE Constellation Mission

4.1 BRITE Mission Objectives

Massive luminous stars, or bright stars, are still one of the most mysteriouscomponents of our Universe [6]. These stars are among the least understooddue to their rapid rotation, strong radiation pressure and stellar wind [7]. Theirlife cycle, their rotation and convection, their history, along with their age couldbe studied by means of asteroseismology [8]. The importance of these massivestars lies on the fact that they dominate the ecology of the Universe [8], so,consequently, scientists are eager to measure their variable behaviour in order toexplore how they work inside. These massive stars are hotter, develop faster anddie earlier [8] with a longer-period variability. Therefore, long observations of atleast three months and at least at two different epochs [9], should be carried out.

The BRIght Target Explorer (BRITE) Constellation mission consists of a groupof Austrian/Canadian nanosatellites that help answering some of the questionsarisen about this topic by means of precise differential photometry [10].

Why a constellation and not a single satellite?

There are several reasons for having more than one satellite. Having multiplesatellites observing the same region of interest will increase the overall duty cycleof observation compared to having one satellite, as, in case of having just onesatellite, for some period of time, the Earth would occult the zone of interest notallowing a continuous observation of the region. In contrast, having two satellitesin two slightly different orbits with different viewing times for the same regionwill double the duty cycle.Furthermore, if we group the satellites in pairs and we place a telescope in eachsatellite prepared to work in only one colour filter, different in each member of apair, then, by collecting colour as well as intensity data, the science capacity isgreatly improved [6] as the spectrum range is increased.

The BRITE Constellation will consist of four LEO nanosatellites in the be-ginning, divided into pairs, both members of a pair with similar orbits, eachmember with different filter colour and each pair with different orbit, whose ob-jective will be to take images (at least 10 times more precise than achievableusing ground-based telescopes), for time periods up to 100 days or even longer,

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4.1 BRITE Mission Objectives

allowing measurements of stellar variability on the order of hours to months. Thesatellites should be able to detect oscillation differences in the order of two partsin 10−5 with a Signal to Noise Ratio (SNR) greater than 2 [10]. To do so, an op-tical, small (3 cm) aperture telescope will collect the light for a camera equippedwith a CMOS detector. These telescopes will have a big field of view of about 24degrees across that will result in images containing from 2 up to 15 (on average4 stars) of the 286 bright stars under study1 (see Figure 4.1) [9]. Having multi-ple bright stars will allow high precision differential brightness measurements ofthese stars, accurate to at least 0.1% per sample [6, 10]. If we assume a missionlifetime of three years, at least a dozen satellites would be needed to observeall those stars of interest. However, BRITE will carefully select a subsample ofthem so that they truly represent the entire group in order to be able to obtaininteresting scientific conclusions out of them.

Figure 4.1: The number of stars to +3.5 magnitude in 25 degrees of field view forBRITE. [6]

These satellites will use new technologies including reaction wheels, a startracker and an optical telescope with a CMOS detector that is compatible withnanosatellite size and power restrictions, all together designed to fit in the Uni-versity of Toronto Space Flight Laboratory (SFL)’s 5 kg, 20 cm × 20 cm × 20 cmCanX nanosatellite bus [11].

The first Austrian satellite, funded by the Austrian Space Program, knownas TUGSAT-1/BRITE-Austria, builds upon the technology of the CanX-2 [7]

1The stars under study are those brighter than visual magnitude of 3.5

8

4.2 BRITE Constellation Satellites

incorporating a high-performance Attitude Control System (ACS). It was desig-nated CanX-3 by the SFL [8, 11]. The other three satellites that will make upthe constellation are the UniBRITE satellite from the University of Vienna, andBRITE-Toronto and BRITE-Montreal from the Canadian Space Agency (CSA)which are currently under review. Both UniBRITE and BRITE-Austria are ex-pected to be lauched in early 2011 [9], representing the first pair of satellites inorbit. The main difference between them will be the filters. A blue filter, rang-ing from about 380 nm to 550 nm will be implemented in one of the satellites,whilst a red filter, ranging from about 550 nm to 850 nm, will be implementedin the other satellite. The filters were selected according to asteroseismologicaland astrophysical needs.

Is BRITE a mere copy or improvement of MOST?

Although both, BRITE and MOST, are missions whose objective is to observeand measure characteristics of stars, among others, they were built to analyzedifferent type of stars. MOST project’s target are miniscule asteroseismic oscil-lations of Solar-type stars, while BRITE is focused on the study of massive stars.Therefore, they can be considered as complementary satellite missions.

Moreover, regarding their structure, the MOST satellite utilizes an instrumentwhose field of view (approximately 0.8 degrees) is too narrow to obtain simul-taneous observations of multiple stars that are far apart in the sky in order toimprove accuracy.

Last but not least, the MOST bus was designed to keep one face pointingtowards the Sun. That means that the targets within the viewing face zone cannotbe observed for more than 7 weeks without being obscured by the Earth. As aresult, characterisation of long-period variability of stars, which is the variablityexpected in many of the brightest stars and one of BRITE’s main objectives, isnot possible with MOST, as the duration of the observations is not long enoughto accomplish this aim [10].


The BRITE Constellation of satellites will be composed by four vitually identicalnanosatellites that will use the Generic Nanosatellite Bus (GNB) developed bySFL. The GNB is a modular spacecraft bus design that provides all basic satellitefunctionality and incorporates a direct energy-transfer solar power system [6].

Each satellite will comprise the following subsystems [12]:

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Structural Subsystem

Each satellite has a cubic structure with a size of 20 cm× 20 cm× 20 cm, madeof aluminium which is nickel-plated (see Figure 4.2), and a weight between 5 and7 kg [8, 11, 9].

Figure 4.2: Structure of a BRITE Satellite. [12]

Thermal Subsystem

Thermal control is provided through passive measures with the help of sensors.Thermal coatings and tapes are applied on every panel of the cube. This will keepthe average temperature between 10C and 30C. The thermal control of individ-ual components is achieved by means of thermal isolation and heat sinking [9, 12].

Attitude Determination and Control (ADC) Subsystem

Accurate determination and control are needed in order to fulfill the missionrequirements. This accuracy will be fulfilled by means of actuators and sensors(see Figure 4.3), such as the new Dynacon’s NanoWheel system, that includesthree reaction wheels and three orthogonal magnetorquer coils which allow 3-axisstability control to the level of 1 arcminute rms, and momentum dumping. Anattitude determination of 10 arcseconds will be provided through a magnetometerand sun sensors, which will enable BRITE to be one of the first operational spacescience nanosatellites. The satellite will also house a miniaturized star trackerintegrated with the instrument. All this equipment will allow control accuracybetter than a degree [7, 9].

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?

Figure 4.3: Attitude control hardware of the BRITE satellite. [8]

Power Subsystem

The power required for the satellites will be obtained through solar cells thatwill convert light into electrical energy. This energy will be stored in batteriesso that energy is available in eclipse phases. On average, 6 W of energy will begenerated [7, 12] with a maximum of 10 W [6].

On-board Computer Subsystem

The satellite will carry three computers [12, 7]:

• One computer will control the payload, i.e. the photometer.• A second computer will carry out the housekeeping tasks.• Finally, a third computer will control the ADC system.

The whole subsystem will ensure functionality in case of failure of one of thecomputers, such as decodification of Earth commands, control of the varioussubsystems and telemetry, and forwarding of the data to the communicationsubsystem for downloading.Serial links using robust, reliable protocols will be used to connect the differentcomputers.

Communication Subsystem

The communication subsystem is responsible for receiving commands from theground stations and transmitting data and telemetry back to Earth. Two patchantennas, shown in Figure 4.4, and a Ultra High Frequency (UHF) receiver aremounted in the satellite.

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4.3 BRITE Orbits

Figure 4.4: Patch antennas mounted on the BRITE satellites. [12]

Payload

As mentioned before, the satellite will carry a photometer instrument thatwill capture images of bright massive stars. This telescope will have only 30 mmof diameter and a maximum length of 100 mm, but a wide field of view. Itwill consist of a CMOS detector coupled with a lens system designed to providethe accuracy required. Moreover, the filters needed in order to take images indifferent spectrums, were designed so that, for a star of 10000 K (which is theaverage temeperature of the target type of stars), both filters would generate thesame amount of signal on the detector, with a maximum transmission of 95% [9].Up to 12 rasters will be taken per image of up to 10 x 20 pixels each [10], andonly sub-rasters of the whole image will be downloaded for further analysis [7].In Figure 4.5 we can see how all these components are integrated in the smallGNB spacecraft.

4.3 BRITE Orbits

The satellites’ orbit will be polar sun-synchronous, with a height of approximately900 km [12], that will lead to a 100 minute orbit period. During this period,one sample image of at least one target field should be taken. Orbits withoutobservations should not exceed 20% of all orbits, and should never exceed 2 daysof duration [10].

4.4 BRITE Communications

BRITE satellites will allow full duplex communications with the ground stations[6]. All the satellites will use the same available set of frequencies. Uploadingcommands and software from Earth will be transmitted in the UHF band bymeans of four pre-deployed rod antennas in the satellite. The uplink data rate

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4.5 Summary of BRITE

Figure 4.5: Components of the GNB BRITE satellite. [12]

will be nominally 4 kbit/s using Gaussian Minimum Shift Keying (GMSK) mod-ulation [6, 7]. The downlink communications will be carried out in the S-band[6]. The S-band antennas will consist of two patch antennas mounted in oppo-site sides of the satellite. The antennas will be fed in phase with equal signals.This configuration will provide a near omnidirectional pattern. Finally, circularpolarisation will be used [7].

Data will be downloaded at a nominal rate of 32 kbit/s, although, in case ofground stations with a high figure of merit, higher rates (up to 256 kbit/s) arepossible [12, 7]. The daily average downlink volume of scientific data can reach6 Mbytes [10], however, typically it is around 2 Mbytes [12]. For data downlink,a Binary Phase Shift Keying (BPSK) modulation scheme will be used, just likeMOST. Therefore, the same demodulator can be used for both missions [13].

Telemetry data will be transmitted in the S-band to the ground station, andin UHF from the ground station to the satellite. The amount of telemetry datasent per day will be at least 180 kByte [7].


In Table 4.1 we can see a summary of the main characteristics of the BRITEsatellites’ structure and communication capabilities [12, 9].

13


Table 4.1: Summary of the main characteristics of the BRITE satellites.

Satellite Specification ValueVolume 20 cm × 20 cm × 20 cmMass 6 kgAttitude Determination 10 arcsecondsAttitude Control Accuracy better than 1

Attitude Control Stability 1 arcminutePower 5.4 W to 10 WTransmitting Power 0.5 WFrequency Ranges (data and telemetry) S-band (downlink), UHF (uplink)Data Downlink Rate 32 kbit/s to 256 kbit/sModulation Downlink BPSKData Uplink Rate 4 kbit/sModulation Uplink GMSKData Volume per Day 2 MByte to 6 MBytePolarisation Circular Polarisation

14

Chapter 5

The GENSO Project

5.1 GENSO Objectives

The Global Educational Network for Satellite Operators (GENSO) project is aworldwide project which may have a great impact on the current concept of com-munication with educational satellites. GENSO can be regarded as a softwarepackage for ground station computers that allows interaction between differentground stations. This will be possible by connecting the ground stations via theinternet so that, for instance, someone in America can use remotely a groundstation in Europe in order to communicate with a certain satellite [14, 15].

The idea of this global network was first discussed in the Ground Station Net-work Conference in Tokyo, Japan, in July 2006. Soon after, the ESA and theInternational Space Education Board (ISEB) accepted the proposal and GENSOwas born [15]. Currently, the project counts with numerous collaborators, par-ticularly universities.

Generally, educational scientific satellites are small satellites that operate on lowpower budgets. It’s structure is similar to that of amateur satellites due to theirlow cost, and usually they use the same frequency bands. Their hardware is notintended to resist high radiations, so therefore, they usually operate in LEOs. Asa result, the operable time per orbit that the satellite is available is just a fewminutes [15, 16]. This fact limits the amount of data that can be exchanged withthe satellite, since increasing the data rate is not a feasible possibility for thesesmall satellites. Furthermore, as a consequence of the small amount of time thatthe satellite is visible for the ground station, most of the time the ground stationwould be in an idle state, that is, wasting its capacity [17].

By means of GENSO, the availability of satellites and the ground stations’ effi-ciency can be drastically increased. If multiple ground stations were used toreceive data from a single spacecraft, the data throughput of that satellite wouldbe positively influenced. In order to do this, GENSO will link multiple groundstations around the world through the internet using an open source software,creating a sense of global coverage.

15


However, increasing the data throughput is not the only scope of the project.Availability of remote uplink through trusted third party ground stations, def-inition of an optional standard solution for the ground-segment hardware, anddownlink error correction are other objectives of this ambitious project.In addition, another important goal of the GENSO project is to encourage stu-dents to continue their education in the radio amateur domain [15, 14].

Mostly, GENSO will connect educational scientific ground stations, which usuallywork in amateur radio frequency bands. Consequently, the project will focus onpackages that support the amateur frequency bands to start with. However, thereare no real restrictions on frequencies, nor restrictions on modulation schemes,operational modes or equipment, since new drivers can easily be distributed [15].

The GENSO network consists mainly of three components [15, 14, 17] (see alsoFigure 5.1):

Central Server or AUthentication Server (AUS). The central server wouldperform authentication of the nodes in the network as well as encryption,acting as a supervisor of the network, and distributing the information(satellite lists and statistics) to the nodes when required. Currently, it islocated at Vienna University of Technology.

Ground Station Server (GSS). The ground station server is sited in the groundstation and controls the connected antennas, TNCs and radio in order tomove the rotators and tune the radio remotely.

Mission Control Client (MCC). The mission control client is an applicationused by satellite operators to control the network’s management of thesatellite.

In other words, by means of the MCC, a satellite operator will tell the GSSrelevant information about the satellite, such as mode, frequencies, etc. Eachspacecraft will have one MCC, however, there is no need to place it in the satellite,but it can be located on any computer connected to the internet. As soon as theAUS authenticates the registration on the network, the MCC will get a groundstation server list (GSSL), which includes all the available ground stations, theirlocation, frequencies, among other necessary data. Once registered, the MCCis responsible of keeping the AUS up to date. If a GSS wants to register onthe network, it would log on to the AUS to get the Participating SpacecraftList (PSL). This list contains all the data from the available spacecrafts, such asstatus, frequency, and Keplerian elements, as well as the satellite MCC encryptionkeys so that the GSS can contact the satellite’s MCC to transfer downlink data[14, 15].

In order to start up the GENSO network, AMSAT-UK has developed a stan-dard ground station hardware which includes common commercial elements [16].

16


InternetMCCGSS

AUS

GENSO

Figure 5.1: Components of a GENSO network.

However, the hardware supported is not restricted to the standard, as new soft-ware drivers of other devices can be written and added.A diagram of a standard ground station is shown in Figure 5.2 below, where theconnection of the GSS to the TNC and the tranceiver is shown.

Transceiver TNC GSS

Control

Audio Data

Figure 5.2: Diagram of a standard GENSO ground station.

Nevertheless, if any individual amateur radio operator would like at any mo-ment to use their ground station as they did in the past, there is an option todisconnect definitely or temporarily from the GENSO network, and reconnect it,if wanted, once they are ready again.

17

5.2 Typical Educational Satellite Features

5.2 Typical Educational Satellite Features

Satellites can be classified according to their mass, as large, medium or small.Most educational scientific satellites belong to the small satellite category, Thiscategory can, in turn, be divided into subcategories, as shown in Table 5.1.

Table 5.1: Classification of small satellites.

Subcategory MassMinisatellite 100-500 kgMicrosatellite 10-100 kgNanosatellite 1-10 kgPicosatellite 0.1-1 kg

Microsatellites (or Microsats) (see Figure 5.3) and nanosatellites are the mostcommon among the academic and amateur spacecrafts, as universities cannotafford big satellites that cost a lot to produce and put on orbit. However, nowa-days, it is common to find cubesats [18]. Cubesats are 10 cm cubic spacecraftsoriginally developed by the Stanford University in California and California Poly-technic State University. They have the advantage (due to their small size) ofsharing a common launcher so that 3 to 6 cubesats can be launched at the sametime, and therefore, decreasing the launching costs [19].

Figure 5.3: AMSAT-OSCAR 51 (Echo AO-51) microsatellite. [19]

5.3 Educational Satellites Orbit

Due to their small size, educational satellites usually have low power available.Moreover, the launch costs in order to put a satellite in a high orbit are signif-icant and would need the spacecrafts to be able to support more radiation. In

18

5.4 Communications

contrast, lower orbits have the advantage of suffering from less propagation de-lay. Therefore, small satellites are usually placed in low orbits between 400 and2000 km with high inclination or polar orbits [19].

Yet, placing the satellites in LEO has a big disadvantage: the satellite is mostof the time out of the line of sight of the ground station antenna (pass timesrange from 12 to 22 minutes). Furthermore, in order to increase the coverage,many satellites are needed, as the footprint of a single LEO satellite is too small.

5.4 Communications

Over the years, technology has evolved forcing the utilizable frequency spectrumto extend (higher frequencies became necessary) so that new amateur satellite ser-vices could be allocated. Educational satellites usually operate at amateur radiofrequencies as they cannot afford their own frequency allocations. In Table 5.2we can see the most common amateur satellite frequency bands.

Table 5.2: Common amateur satellite frequency allocations.

Band Frequencies (MHz) Approximate WavelengthVHF 144–146 2 mUHF 435–438 70 cmL-Band 1260–1270 23 cmS-Band 2400–2450 13 cm

The combination of uplink frequency, downlink frequency, and transmissionmode are all lumped together into satellite modes.

In the table below, there is a list of common satellite modes used by amateursatellites.

Each band in Table 5.2 can be used for both downlink and uplink, however itis common to have dual frequencies that operate simultaneously [19]. However,you can also find satellites operating simultaneously at L-Band and S-Band.

Table 5.3: Common amateur satellite modes.

Traditional Mode Designator New Mode Designator Downlink UplinkB V/U 70 cm 2 mJ U/V 2 m 70 cmS S/U 70 cm 13 cm

Our ground station, will be able to use 2m/70cm/13cm bands for downlinkand uplink, therefore it will work for every satellite operating on modes U, V andS.

19

5.4 Communications

Regarding the modulation schemes, amateur satellites commonly use frequencymodulations, such as Frequency Modulation (FM) or Frequency Shift Keying(FSK). Data rates vary remarkably with bandwidth and modulation used. Nor-mally, nominal data rates of 1200 baud, 9600 baud, and up to 78400 baud are used[19, 20]. However, higher rates are also possible.

20

Chapter 6

Concept of a Multi-Mission Ground

Station

6.1 General Concept of a Ground Station

A ground station is a terrestrial terminal station used in communicating withspacecrafts and/or satellites. Its location is usually on the surface of the Earth,however, it can be located within the Earth’s atmosphere too [21]. A telecom-munication link between a satellite and the ground station is achieved by trans-mitting and receiving radio waves in high frequency bands when the satellite iswithin the ground station’s line of sight.

Our ground station should be able to support different missions in LEO as wellas being flexible for future modifications. Therefore, in order to achieve this andkeep it simple, the ground station can be divided into three segments or layers[22] (see Figure 6.1 and Figure 6.2):

Front End Segment The front end segment contains all the equipment ope-rating at RF down to the first intermediate frequency [23], including theantenna and rotators.

Signal Processing Segment The signal processing segment is also called backend [23]. It includes the elements and converters between the analog andthe digital domains, as, for instance, the tranceivers, modems and TNCs.

Data Processing Segment This subsytem is in charge of the specific data pro-cessing carried out usually by Personal Computer (PC)s.

21


FRONT END

SIGNAL PROCESSING

DATA PROCESSING

Figure 6.1: Division of a ground station into three segments.

S-Band UHF-Band VHF-Band

Converters Tranceivers (De)modulators

Computer

Figure 6.2: Overview of the three segments of a ground station.

22


In the case of our ground station, it will support Very High Frequency (VHF),UHF and S-Band communications (see Table 6.1) and will allow both transmi-ssion and reception.

Table 6.1: Scientific bands and frequencies of interest for the ground station.

Band (MHz) Frequencies of Interest (MHz) Reference WavelengthVHF 30 – 300 144-146 2 mUHF 300 – 3000 430-440 70 cmS-Band 2000 – 4000 2000–2450 13 cm

Moreover, taking a closer look on these three segments, Figure 6.3, shows howthe ground station’s blocks can be easily classified to fit into each of these seg-ments and can be considered as independent subsystems.

Duplexer

Filter LNAPolarization

Recovery Unit

Polarization

SelectorFilter HPA

Internet

Up-

Converter

Down-

Converter

Transceiver Modem TNC

Figure 6.3: A closer look into the three segments.

According to other publications [24], in which, a reference model is proposed inorder to simplify the specification of the ground station’s capabilities, the signalprocessing segment would correspond to the transmit and receive pipelines, and,the data processing segment would implement the session level and some mastergroup tasks.

However, a ground station system is not only composed of the communication-devoted system, but of other sections which make communication possible.

23


Power

Supply

&

Control

Weather

Protection

Lightning

Protection

Polarization

Control

Tracking

System

Rotator

&

Controller

GROUND-

STATION

Figure 6.4: Other subsystems of a ground station.

As can be seen in Figure 6.4, these include, but are not limited to,• a polarization controller which enables the user to choose a polarization

between horizontal linear, vertical linear, right handed circular (RHCP)and left handed circular (LHCP),

• a lightning protection system that protects the station from electric over-load,

• a rotator and its controller to position the antenna towards the desiredsatellite,

• a tracking system that provides the antenna with the capability of followingthe satellites to enable communication,

• a power supply and a control system to provide the adequate power neededfor operating,

• and finally, a weather protection unit that, for instance, forces the antennato stay in rest position during strong winds or snow storms.

24

6.2 Frequency Plan

6.2 Frequency Plan

The first step in order to design the ground station was making a frequency plan,where the bandwidth needed could be seen, as well as the frequency separationbetween the different missions and the possible combination of them in uplinkand downlink. Table 6.2 shows the compilation of the uplink and downlink fre-quencies used in the missions accomplished in the ground station.

Table 6.2: Frequencies of the satellite missions considered.

Mission Uplink (MHz) Downlink (MHz)

BRITE 437 2200146

COROT – 2300

GENSO2300–2450 2300–2450435–438 435–438144–146 144–146

MOST 2055 2232

However, the objective of this thesis was to design the S-band front-end of theground station. Therefore, the only frequencies to take into account are the onesin the S-band that are shown in the Table 6.3, which are, naturally, included inthe frequencies that our ground station will support, according to the Table 6.1.Within the S-band amateur radio frequency bandwidth, the band that is generallyused is 2400-2450 MHz. Therefore, the design of the ground station will focus onthese frequencies for GENSO, as shown in the table below.

Table 6.3: Frequencies in the S-Band.

Mission Uplink (MHz) Downlink (MHz)

BRITE – 2200COROT – 2300GENSO 2400–2450 2400–2450MOST 2055 2232

As a suitable solution of an implementation of this ground station, a switchcan be used to select between GENSO and non-GENSO. COROT, BRITE andMOST use the scientific bands, while GENSO uses the amateur frequency bands.On the one hand, a duplex filter will separate the transmit and receive bands

25

6.3 Block Diagram of the Ground Station

for non-GENSO frequencies enabling full duplex communication in the scientificbands. Then, another switch will be placed to select between COROT, BRITEand MOST.

For GENSO, full duplex communication is not possible, forcing to select be-tween reception and transmission at a given moment.

In the Figure 6.5 below, an outline of the ground station is shown, without go-ing into details describing the transmission and reception pipelines of the differentsatellite missions.

DUPLEX

FILTER

RX COROT

RX MOST

GENSO TX

GENSO RX

TX MOST

GENSO

COROT, BRITE, MOST

2.20 – 2.30 GHz

2.03 – 2.11 GHz

2.40 – 2.45 GHz

NON-GENSO

RX

TX

RX BRITE

Figure 6.5: Ground Station S-Band Outline.


As described in the previous section, by means of switches, the different optionscan be selected easily. The design had to be kept simple, modular and efficient.For instance, the same demodulator can be used for BRITE, COROT and MOSTwhen receiving, reducing the complexity of the ground station block diagram andincreasing its efficiency as it is shown in Figure 6.6.

A distinction is also made between the elements situated at the antenna mountingplace (i.e. outside), the elements that are located on the roof but not outside (inan electrical cabinet), and, finally, the elements that are sited in a room inside thebuilding. This way, the duplex filters, the filters and the LNAs will be mounted

26


along with the feed in the parabolic dish focus to minimize losses because of longcables (see Section 7.13) . The polarization recovery unit, the polarization selec-tor, the HPAs, the transmission filters and the up- and downconverters will besituated in a cabinet on the roof (see Chapter 7). The rest will be located insidethe building as the losses in the cables after the downconverter and before theupconverter have not so strong impact on the SNR and, furthermore, the groundstation data processing segment is more convenient to be located inside.

Double components are used in the outside elements due to the dual polari-zation ability of the feed. Both vertical and horizontal linear polarizations areavailable until the polarization recovery unit selects the wanted one.

27

6.3B

lock

Diagram

ofth

eG

round

Station

TNC

+

Modem

TNC

+

Modem

TNC

Feed

LNAPolarization

Recovery

Unit

Downcon

verter

Transciever GENSO

Upconv

erterPolarization

Selector

140 MHz

HPA

Duplex

FilterLNA

Polarization

Recovery

Unit

Downconv

erterModem

BRITE

COROT

MOSTModemUpconv

erterPolarizatio

n SelectorHPA

Rotator

Controller

Internet

Azimut /

Elevation

Rotator

Parabolic Dish

GENSO

COROT

BRITE

MOSTCOROT

BRITE

RX MOST

TX MOST

RX

TX

Outside

Inside

Filter2400 –

2450 MHz

Filter2400 –

2450 MHz 140 MHz

140 MHz

140 MHzFilter2030 –

2110 MHz

2.03 – 2.11 GHz

2.20 – 2.30 GHz

Roof / Elect. Cabinet

Rx

Tx

TranscieverUHF

VHF/UHF

Figure

6.6:G

round

stationS-b

and

diagram

.

28

Chapter 7

Building Blocks Analysis and

Selection

When designing a ground station, every component has to be carefully analysedand selected in order to obtain a good overall quality, minimum losses and areasonable cost. Some components are more critical than others but all of themare necessary, affect the other components and have a specific task that will beexplained along this chapter. All these components are shown in Figure 6.6 inSection 6.3.

7.1 Antenna

For satellite communications a high directivity and a high gain are needed. More-over, full duplex operation should be provided. In this case, a parabolic dish isthe best option. Parabolic dishes have an acceptable dimension at microwavefrequencies regarding gain, a reasonable bandwidth and, profitably, as their dia-meter increase, so does their gain [25, 26, 27]:

G =

(

π ·Dλ

)2

· η (7.1)

where D is the dish diameter in meters, λ is the wavelength in meters, and η isthe total efficiency.

In addition, another feature is that the Half Power Beam Width (HPBW), isinversely proportional to the diameter [25, 26, 27].

HPBW =21

D · f (7.2)

where f is the frequency in GHz and the result is in degrees.The total efficiency is a combination of different efficiencies, η = ηr · ηat · ηs · ηo

[28, 29], where:

• ηr, is the radiation efficiency, which deals with the ohmic losses. Due tothe fact that the feed usually doesn’t have many losses and the reflector is

29

7.1 Antenna

typically metallic with high conductivity, this efficiency can be consideredas 1.

• ηat, is the aperture tapper efficiency and measures the uniformity of theelectric field across the reflector, which tends to decrease as we move awayfrom the main axis, leading to a reduction in the gain.

• ηs, is the spillover efficiency and measures how much radiation is actuallybeing reflected, as some of it overflow the reflector. See Figure 7.1.

• ηo, includes all other effects that affect the total effciency, such as, thesurface error, the aperture blockage, the cross polarization, and the non-ideal feed center.

Focal Point

Spillover

Aproximated

Radiation

Pattern

Reflector

Surface

Figure 7.1: Losses due to spillover.

The efficiency improves, as well as the cross polarization, as the ratio F/Dbetween the focal distance, F, and the diameter of the dish, D, increases [30].However, the spillover gets worse. So we reach a tradeoff situation. And, when

30

7.2 Feed

increasing the diameter in order to improve gain, windloading, rotator apparatus,and mounting structure should be taken into account.

Typically, parabolic reflectors have a total efficiency between 55–75%, a F/Dratio between 0.3–1, and a gain between 30–40 dB [26, 27].

Furthermore, the ground station will use Kepler elements to predict where thesatellite is expected to be and will point the antenna towards it using motorsthat drive it from position to position. These motors and servos should provideenough power to overcome inertia and friction.

For our ground station, a 3.65 m parabolic dish with F/D = 0.4, was chosen.Regarding the frequencies that it will work at, and an efficiency of about 55%, itshould provide a gain of about 38 dB.

7.2 Feed

The feed is one of the most important parts of an antenna system. It doesn’t usu-ally introduce much gain but it should illuminate the dish properly when placedat the adequate focal distance. This focal distance depends on the reflector’s F/Dratio, so the feed should, therefore, match with the selected reflector. Ideally, thefeed should illuminate the dish at the edges 10 dB below that in the center [31].

Moreover, the narrower the beamwidth of the antenna, the better, as it willsuffer from less interference from the ground due to reflected RF energy andsignal blockage [32].

Usually, horns are used, however, depending on the F/D ratio, different feedscan be easily built to match the reflector appropiately. In our case, the optimalF/D ratio regarding the dish selected would be 0.4, as mentioned before.

7.3 Switches

RF switches were necessary in my design of the ground station in order to keepthe design modular and simple. Nevertheless, splitters could also have been usedin some cases, with the disadvantage of higher losses, but with the advantage ofenabling, for instance, parallely feeding components and monitoring the signalat the same time [22]. The switches are typically mechanical so they provide fullbandwidth operation with minimum insertion loss.

31

7.4 Duplex Filter

7.4 Duplex Filter

The duplex filter is a passive filter that avoids the transmit pipeline signal to getinto the receiver pipeline, but allows full duplex operation with the antenna, asshown in Figure 7.2. Full duplex operation entails receiving and transmitting atthe same time.

Typically, in the pass bands, it introduces an insertion loss between 0.1 and1 dB and, in any case, a high rejection out of bands.

Scientific Reception

Pipeline(MOST, COROT, BRITE)

Scientific Transmission

Pipeline(MOST)

Scientific

Band

Amateur

Band

_ _ _

2.20 – 2.30 GHz 2.03 – 2.11 GHzDuplex

Filter

f

f f

Figure 7.2: The duplex filter of our ground station.

In the case of our ground station, it will separate the scientific transmissionpipeline, from the reception pipeline, enabling full duplex operation in the scien-tific band. The duplex filter will be one of the first components in our receptionpipeline, so it is desirable to have a low insertion loss in order to minimize the noisetemperature. Therefore, a duplex filter from General Dynamics (see Table 7.1)with only 0.1 dB insertion loss was selected.

Table 7.1: Duplex filter selected.

Manufacturer General DynamicsModel 112225-01Passband 1 2025–2120 MHzPassband 2 2200–2300 MHzRejection out of Bands 80 dBInsertion Loss 0.1 dB

32

7.5 LNAs

7.5 LNAs

The LNA’s function is to amplify the incoming RF signal that arrives with lowpower before the consecutive stages add more noise, provided that the LNA addsvery little noise itself. It should be placed as close to the antenna as possible inorder to have the highest signal possible.

Owing to the fact that the LNA is one of the first blocks in the receive pipeline,it will be determinant in the whole system’s noise figure, therefore, a low noisefigure for this device is crucial. Furthermore, a high gain is necessary to providethe following stages with enough signal power level to be able to process thesignal. Naturally, it should have a suitable bandwidth regarding the operatingRF band.

In addition, the input and the output impedances should be matched withthe previous and the following stage, respectively. Usually, Rin = Rout = 50Ω.Moreover, it would be convenient that the LNA has enough linearity and a highthird-order interception point, in order to have a large dynamic range at theinput.

However, all these characteristics are not achievable at the same time, so acompromised solution should be reached.

Some typical values are shown in the table below, Table 7.2:

Table 7.2: Typical LNA values.

Feature Typical Value

Noise Figure 1 dBGain 30 dBThird-Order Interception Point −10 dBm

For the GENSO receiving pipeline, the LNA described in Table 7.3, was chosen:

Table 7.3: GENSO selected LNA.

Manufacturer Ciao WirelessModel CA23-3034Passband 1 2400–2600 MHzNoise Figure 0.7 dBGain 32 dB

On the other hand, for the scientific reception pipeline, i.e. COROT, BRITEand MOST, the LNA selected was the one described in Table 7.4 with a differentfrequency pass band but similar noise figure.

33

7.6 Bandpass Filters

Table 7.4: Scientific band selected LNA.

Manufacturer Kuhne ElectronicModel 222 AH HEMTPassband 1 2200–2400 MHzNoise Figure 0.5 dBGain 30 dB

7.6 Bandpass Filters

Bandpass filters were placed in front of the LNA’s and after the HPA’s. As men-tioned before, the filters in front of the LNA’s were used to avoid the saturationof the LNA and should have a low noise figure, as it affects the system’s noisecritically.

For the scientific reception band1, the duplex filter already filters most of theunwanted frequencies, so a bandpass filter following the duplex filter would notbe necessary.Regarding the filters following the HPA’s, these limit the frequency band of thelast output spectrum reducing the emissions produced by the amplifier’s non-linearity [32].

The chosen bandpass filters are shown in Table 7.5. For GENSO receptionpipeline, the filter was selected according to its insertion loss, due to the factthat this component is one of the first in the reception chain and so, therefore,affects remarkably the system noise temperature.

Table 7.5: Selected filters for the ground station.

MOST TX GENSO RX GENSO TX

Manufacturer General Dynamics Miteq Delta MicrowaveModel 112084-01 FCL4-2400-100 S1571Bandpass (MHz) 2025–2120 2340–2470 2400–2485Rejection out bands (dB) 120 80 90Insertion Loss (dB) 0,1 0,5 1

7.7 HPAs

In the transmission pipelines, the power has to be adjusted so that it is enough toreach the satellite with a reasonable level and to compensate losses in the S-band

1Reception of COROT, BRITE and MOST

34

7.8 Polarization Selectors and Polarization Recovery Units

satellite systems [32]. These power amplifiers provide the necessary gain, mini-mum RF loss and undesired interaction among the RF signals in order to fulfilthis requirement. It is the most critical active component in transmission. Typ-ically, for the LEO S-Band, 50 W output power from these amplifiers is enough[1], although we can find amplifiers that provide up to 130 W.

For our ground station, two HPAs were needed, one for the MOST transmissionpipeline, and another one for GENSO. The chosen amplifiers are specified inTable 7.6.

Table 7.6: Selected HPAs for the ground station.

MOST GENSO

Manufacturer Empower RF Sys Empower RF SysModel 4026-GCS5A5DMP 4053-GCS5I5KRRBandpass (MHz) 2025–2120 2400–2500Noise Figure (dB) 7 7Gain (dB) 52 56Output IP3 (dBm) 60 651 dB Compression Point (dBm) 50 56Saturated Output Power (dBm) 52.04 57

7.8 Polarization Selectors and Polarization

Recovery Units

The ground station will be able to transmit in linear polarization and circularpolarization by means of a dual polarized feed. Both horizontal and verticalpolarizations are available and can be combined to produce circular polarization.With the polarization selector, the desired transmitting polarization is chosen.In reception, arbitrary polarizations states will be received but can be recoveredby combining the two available linear orthogonal polarization states by means ofthe polarization recovery unit.

7.9 Upconverters and Downconverters

Up- and down-converters provide a frequency translation between an Interme-diate Frequency (IF) (typically 140 MHz), and the actual uplink and downlinkfrequencies, respectively. Its structure is shown in Figure 7.3.

For GENSO, the same Local Oscillator (LO) is used for both downconverterand upconverter. For the scientific band, the LO can also be shared between

35

7.10 Modulators and Demodulators

N Multiplier

Phase-locked

oscillator

Fixed frequency

crystal

reference

S-Band input IF output

IF input S-band output

DOWNCONVERTER

UPCONVERTER

Figure 7.3: A fixed-frequency converter used in Earth Stations.

uplink and downlink pipelines. Moreover, some converters may be included justas a module to be attached to the transceiver.

The upconverter and downconverters would desirably provide a good frequencyresponse in terms of gain flatness, group delay and out-of-band rejection as it isthe main bandwidth-limiting device within the RF front end of the ground station[32]. Typically, upconverters are capable of providing the RF signal with a powerlevel in the range of −60 to −20 dBm.

7.10 Modulators and Demodulators

A modulator-demodulator (modem) is the device in charge of modulating ananalog carrier signal to encode digital information, and also, in charge of de-modulating the received signal to decode the transmitted information. Differentmodems are used in the ground station in order to fulfill the needs of the differentsatellite missions.

For the GENSO Project, for instance, this task is carried out by a special com-binated TNC-modem. In addition, MOST project uses another assigned modemto modulate the MOST signal. Finally, the reception pipeline for the scientificband shares a satellite modem working as a demodulator among BRITE, MOSTand COROT, described in Table 7.7, which reduces the cost and complexity ofthe ground station.

36

7.11 Transceivers

Table 7.7: Datum Systems PSM500 satellite modem specifications.

Modulation Demodulation

Information Rate (kbps) 1.2–29500 1.2–29500Required Eb/No for 10−5 C-QPSK (dB) 9.6 9.6Return Loss (dB) 20 20Transmit Output Power (dBm) +5 to −35 —Receive Input Range (dBm) — −20 to −84Power (VAC) 90–264 90–264Operating Temperature (C) 0–50 0–50

7.11 Transceivers

Transceivers perform the tasks of both a transmitter and a receiver, sharing mostpart of its circuitry. They convert from baseband domain to RF domain with highdata transmission speed. The proposed ground station will use one transceiver inorder to receive and transmit in the amateur radio frequency bands (S-Band, UHFand VHF) for GENSO, and a transceiver in the BRITE transmission pipeline.

7.12 TNCs

The TNC is the device resposible for the processing of the High-level Data LinkControl (HDLC) and/or the AX.25 protocols and for the sending of the datato/from the PC [22]. It is connected to a computer terminal and a transciever,so that, data from the terminal is formatted into the proper protocol and also,so that it provides an interface to the user. Typically, the TNC and the modemcan be found together in a single device, which is called TNC, but is actually aTNC/modem combination. In case of BRITE, a mission specific TNC is used,which includes a modulator [22]. For GENSO, because there is no specific com-mon configuration, in some cases, a direct connection between the audio connec-tors of the transceiver and the PC sound card can be implemented in order toperform the analog to digital, and, digital to analog conversion in the PC [22].All protocol layers are, then, implemented in software.

7.13 Cables and Waveguides

Care should be taken when dealing with the cables and waveguides. These arenecessary but introduce many losses, especially at high frequencies. We will usesemirigid coaxial cables to connect the outdoor devices inside the antenna mount,high quality coaxial cables to take the RF signal to the inside, and possibly, lower

37

7.14 Connectors

quality VHF coaxial cables in the stages following the downconverter or precedingthe upconverter, that is, when the signal is in IF. In the Table 7.8 below, we cansee the typical attenuations for different types of cable.

Table 7.8: Typical attenuation values for cables.

Cable Typical ValueSemi-Rigid 0.50 dB/mRF Cable 0.24 dB/mVHF Cable 0.05 dB/m

In a closer look, our ground station will use specifically the cables shown inTable 7.9 to interconnect the components.

Table 7.9: Specifications of cables used in the ground station.

Ecoflex 15 H2000-FLEX

Diameter (mm) 14.6 10.3Impedance (Ω) 50 50Capacity (pF/m) 77 80Velocity Factor 0.86 0.83Conductor stranded copper copperDielectric PolyEthylene (PE) PEMinimum Bending Radius (mm) 70 100Max. Power (40 C at 1000 MHz) (W) 560 310Typ. Attenuation2 (dB/100 m) 16.3 22.0

7.14 Connectors

There are two connectors per cable, therefore, the losses that entail have to betaken into account. SubMiniature version A (SMA) connectors will be used forthe outdoor devices inside the antenna mount. Typically, they present a loss of0.2 dB at S-band, and are designed for its use with semi-rigid cables. In contrast,for the indoor components and the rest of the outdoor elements, N connectorswill be used. These connectors are hard, humidity resistant and medium size.Their loss is, typically, about 0.2 dB at RF frequencies and 0.1 dB in VHF.

The ground station needs about 20 connectors. Consequently, aproximately3 dB are lost in these connectors. This fact is something that has to be takeninto account in order to achieve a good design.

38

Chapter 8

Propagation Losses

In satellite communications, as oppossed to most terrestrial communications, theelectromagnetic waves have to travel long distances to reach their destination.In particular, these waves need to go through the atmosphere, which, at certainfrequencies, can entail significant effects on the waves’ properties.

In order to succeed in communicating, a certain SNR has to be maintained.Therefore, propagation effects have to be taken into account as they tend to causetransmission losses which can seriously affect this ratio.

8.1 Propagation Effects Classification

There are many different ways of classifying the propagation effects at microwavefrequencies. Commonly, they are classified according to where they take place[33]. Thus, we can distinguish between local effects happening in the groundstation’s surroundings, atmospheric effects, and free space effects.

Concerning the atmosphere, it can be in turn divided into layers, as the at-mosphere’s behaviour and content varies with pressure and altitude. Hence, theeffects can be subclassified according to the layer where they happen. The lay-ers affecting most the radiowave propagation are the troposphere (or non-ionizedlayer) and the ionosphere.

In Table 8.1 we can see the main effects that can occur along the wave’s pro-pagation path. Nevertheless, depending on the operating frequency range andelevation angle, some effects become more relevant than others. For instance, atfrequencies above 10 GHz, rain attenuation, gaseous absorption and clouds arethe most affecting effects, whereas, at frequencies below 10 GHz, ionospheric scin-tillation and Faraday rotation increase their importance. Tropospheric refractionand fading, can, however, happen at any frequency, especially, when rain and gasattenuation have a low value and low elevation angles are used [33].

39

8.2 Propagation Effects at S-Band

Table 8.1: Classification of Propagation Effects.

Local EffectsEffects of clouds and fog (dB)Effects of dust and sand (dB)Effect of snow (dB)

Tropospheric EffectsClear Air

Refraction and Multipath Fading (dB)

Tropospheric ScintillationWave-Front IncoherenceBeam Spreading (dB)

Defocusing (dB)Gaseous Attenuation (dB)Bandwidth LimitationsFading due to Elevation Angle

PrecipitationRain Attenuation (dB)Depolarization

Ionospheric EffectsFaraday Rotation (degrees)

Propagation Effects dependent on TEC1

XPD2 (dB)Range Delay (m)Excess Time (s)Phase Advance (rad)Doppler Frequency (Hz)Dispersion (s/Hz)

Ionospheric Scintillation (dB)Ionospheric Absorption (dB)

OthersFree Space Loss (dB)


The frequency range between 1 and 4 GHz is a range that is only affected slightlyby the Earth’s atmosphere [26]. However, it is important to know to what extentis this true. Therefore, it is advisable to predict the magnitude of the effects inthis frequency range [33].

1 TEC is the total electron content in el/m2

2 Cross Polarization Discimination

40


8.2.1 Ionospheric Effects

Faraday Rotation

Faraday rotation is the rotation of the polarization plane during its transitthrough the atmosphere. It affects linear polarization due to the fact that alinearly polarized wave can be considered to have left and right circularly polar-ized components with different refraction indices. As a result, angles of rotationcan vary in the range of a few degrees to up to many complete rotations. Thiseffect depends on the length of the path, frequency, and, orientation with respectto the Earth’s magnetic field [34].

The angle of rotation, in radians, can be calculated using the following Equation 8.1[35, 34, 26]:

φ = 2.36× 102BavNT

f 2(8.1)

Where:• Bav is the Earth’s average magnetic field in W ·m−2 or Teslas,• NT is total electron content in electrons ·m−2,• f is the frequency in GHz.

A typical value for the average magnetic field is 7 × 10−21 Teslas [34]. Re-garding the Total Electron Content (TEC) (NT , or electron concentration), it isa parameter that describes the electron density in the ionosphere. It is reallyvariable as it depends on the solar radiation, i.e., the time of the day, the Suncycle, the time of the year and present geomagnetic storms [26]. In order to beable to perform the calculations, an average value of 1.2× 1017 is used.

It can be observed that Faraday rotation is inversely proportional to the fre-quency squared, therefore, as we increase the frequency, the effect becomes lesssignificant. This effect does not depend on altitude nor elevation angle. Figure 8.1shows the values of Faraday Rotation within the ground station bandwidth.

Cross-Polarization Discrimination

Directly related to Faraday’s rotation is the Cross-Polarization Discrimination(XPD). It is defined as the difference between the cross-polarized componentand the copolarized component due to the depolarization of the wave as it passesthrough the atmosphere. In case of circularly polarized waves, the Faraday shiftwill not affect the polarization components.

It can be easily calculated using Equation 8.2 [36, 35, 27, 37].

XPD = −20 log(tanφ) (8.2)

Where φ is the Faraday rotation angle in radians.

41


Faraday Rotation (degrees)

1,89

2,69

1,97

2,18

2,28

0

0,5

1

1,5

2

2,5

3

2000 2050 2100 2150 2200 2250 2300 2350 2400 2450 2500

Frequency (MHz)

Deg

rees o

f R

ota

tio

n

Figure 8.1: Faraday Rotation.

Phase Advance, Range Delay and Time Delay

Due to the refractivity of the ionosphere, the receiver may encounter a wave witha different phase to that expected. The phase is actually advanced a certainnumber of cycles depending on the operating frequency and the TEC (NT ). Thenumber of cycles can be obtained by means of Equation 8.3 [33], where ∆Φ isgiven in radians.

∆Φ =1.34× 10−7

fNT (8.3)

The frequency, f , is expressed in Hz, and NT in electrons/m2.This phase shift can be considered as a change in the apparent path length or

range. This range delay will depend on the frequency of the wave and the TECof the ionosphere. Equation 8.4 shows how it can be calculated [34].

∆r =40.3

f 2NT (8.4)

Where, again, f is expressed in Hz, NT is expressed in electrons/m2, and ∆ris the range in meters. Nevertheless, this change in the path length can also beturned into a time delay or excess time easily by using Equation 8.5 [35, 34].

t =40.3

cf 2NT (8.5)

42


Where c is the speed of light in vacuum in m/s, f is the frequency in Hz, NT

is the TEC in electrons/m2, and t is the time delay in seconds.In Figure 8.2 the behaviour with frequency of the range delay and the time

excess for the different missions can be observed. There is no dependence withelevation angle and altitude, just with frequency.

Range Delay and Excess Time

0,81

0,840,93

0,97

1,15 3,81E-09

2,79E-09

2,68E-09

3,23E-09

3,09E-09

0

0,2

0,4

0,6

0,8

1

1,2

1,4

2000 2100 2200 2300 2400 2500

Frequency (MHz)

Ran

ge D

ela

y (

m)

2,0E-09

2,2E-09

2,4E-09

2,6E-09

2,8E-09

3,0E-09

3,2E-09

3,4E-09

3,6E-09

3,8E-09

4,0E-09

Excess T

ime (

seco

nd

s)

Range Delay

Excess Time

Figure 8.2: Range Delay and Time Excess.

Doppler Frequency

Doppler frequency is the derivative of the phase with respect to time, i.e., thevariation of the phase with time. In turn, for the atmospheric constribution toDoppler frequency, the phase is proportionally related to the TEC. Due to thedifficulty of portraying TECs behaviour with time, we consider the TEC as aconstant. As a result, the contribution of the atmosphere to the existing Dopplerfrequency will be 0 Hz.

Dispersion

Dispersion occurs due to the fact that the time delay is not equivalent for allfrequencies, i.e. it is frequency dependent. Dispersion is defined as the rate ofchange of the delay with respect to frequency [34]. It can decrease the amplitudeof the wave, and introduce frequency modulation.

43


Equation 8.6 shows how dispersion can be calculated in s ·Hz−1, when the TEC(in electrons/m2) and the operating frequency (in Hz), are known.

D = −80.6

f 3NT (8.6)

The differential delay, in seconds, associated to the lower and upper frequenciesof the signal is described in Equation 8.7

∆t = −80.6

cf 3∆fNT (8.7)

Figure 8.3 shows the evolution of the dispersion and the phase advance withfrequency for the missions supported by the ground station. Both effects showno variation with altitude and elevation angle.

Dispersion and Phase Advance

44,37

42,2

45,3345,38

41,34

49,28

3,70909E-18

2,89091E-18

2,32292E-18

2,1875E-18

2,705E-18

40

41

42

43

44

45

46

47

48

49

50

2000 2100 2200 2300 2400 2500

Frequency (MHz)

Ph

ase A

dvan

ce (

rad

)

0,0E+00

5,0E-19

1,0E-18

1,5E-18

2,0E-18

2,5E-18

3,0E-18

3,5E-18

4,0E-18

Dis

pers

ion

(s/H

z)

Phase Advance

Dispersion

Figure 8.3: Dispersion and Phase Advance.

Ionospheric Scintillation

Ionospheric scintillation are rapid variations in the electron density that cancause, among others, fading of the signal [36]. This fading can be severe and canlast for several minutes, however, it will not be taken into account for the linkbudget as it just appears for a very short time interval.

44


Ionospheric Absorption

For frequencies above 70 MHz, and medium latitudes, ionospheric absorption canbe negligible, as the waves will penetrate the ionosphere with no substantialdissipative attenuation [35].

8.2.2 Tropospheric Effects

Within the tropospheric effects, we can distinguish between clear air effects andeffects happening when there is precipitation (see Table 8.1). Next, each effectwill be explained in more detail.

Tropospheric Scintillation

It is important not to confuse tropospheric scintillation with fading effects in theatmosphere. They both entail variations in amplitude due to irregularities inthe path, however, fading refers exclusively to slow variations, of seconds or evenminutes, whilst, scintillation refers to very rapid fluctuations [26].

Tropospheric scintillation consists of wave-front incoherence and beam spread-ing. Wave-front incoherence depends on frequency, elevation angle and an-tenna diameter. Nevertheless, this effect is negligible in comparison with beam-spreading so it is not taken into account in calculations [38]. Beam spreading,however, can cause losses of nearly 1 dB depending on the elevation angle. It isindependent of frequency for the range of 1 to 100 GHz and it is negligible atelevation angles above 3 for latitudes below 53 which is the case of Vienna1

[38].Nonetheless, a guide to calculate the beam spreading loss following the Inter-

national Telecommunication Union (ITU) recommendations [38, 39] is describedin Appendix A.

Refraction and Fading

The refraction index varies with height, and as a result, the waves do not travelin straight lines through the troposphere, experiencing bending or refraction [33].Refraction becomes dominant at elevation angles greater than 4 however, theprediction model used for calculating the amount of refraction has only beentested at frequencies above 7 GHz. Therefore, losses for elevation angles above4 at our frequency range are assumed negligible [38].

On the other hand, for elevation angles less than 5 fading is the predomi-nant effect. It has a similar character to multipath fading on terrestrial links[38]. Moreover, we can distinguish two kinds of fading: shallow and deep. InAppendix B, step by step calculations for refraction and fading effects are de-tailed [38, 40].

1 Vienna’s latitude is 48.22

45


Defocusing

The signal’s level can also be affected by dispersion or antenna’s beam narrowingdue to the dependence of the atmospheric refraction on elevation angle. Thiseffect is called focusing and defocusing of the wave, and it can be neglectedfor elevation angles greater than 3. Our ground station will work at elevationangles above 3, so, this effect will not be taken into account in the link budget.Nevertheless, further data and sample calculations are shown in Appendix C [39].

Gaseous Attenuation

Gaseous molecules in the atmosphere, such as water vapour and oxygen, absorbenergy from waves that pass through them, leading to some attenuation. Atour operating frequency band it is not a very significant loss, as it is workingfar away from the highest absorption lines. Withal, it will cause some attenu-ation, depending on the frequency and climate of the station’s location. Thesecalculations are shown in detail in Appendix D [32, 41, 42].

Bandwidth Limitations

When working at frequencies near the absorption lines of atmospheric gases, somedispersion may appear due to anomalies in the refractive index. However, thesechanges are not significant for the bands and vicinity where space communicationsare allocated. Therefore, it can be neglected.

Fading due to low Elevation Angles

For short periods of time, and for elevation angles less than 5 the signal’s levelcan vary severely. For instance, at 7 GHz, the signal may increase up to 8 dBor decrease 16 dB at an elevation angle of 3.3. Unfortunately, there is still norecommended model available in order to predict this increment or fade of thesignal [43].

Rain Attenuation

Rain attenuation can result in severe losses at high frequencies. However, at thefrequency range of 2 to 2.4 GHz, rain attenuation has only a slight effect on thetotal of all the propagation losses [38]. Furthermore, the attenuation due to rainrises as the number and size of the raindrops increase, as well as, as the lengthof the path increases [34, 25, 27].

Rain attenuation depends on the location of the ground station, the elevationangle, the frequency of operation, and, naturally, on the rainfall rate at the groundstation’s location.

46


In Appendix E a step-by-step guide is given in order to calculate the attenua-tion due to rain. Also, specific calculations for our ground station can be foundthere [38, 44, 45, 46].

Depolarization

Depolarization is the alteration of the polarization state of a wave as it passesthrough an anisotropic medium, such as clouds. It may be measured by means ofcross-polarization discrimination, however, it is negligible for frequencies below6 GHz [34, 38, 47].

8.2.3 Local Effects

Effects of Clouds and Fog

Clouds and fog can produce many losses for low elevation angles at high frequen-cies. As the elevation angles increases, their effect becomes less significant, andeven for low elevation angles, their effect can be neglected at frequencies below5 GHz [48, 33, 49].

Effects of Dust and Sand

All that is known about the effects that dust and sand can have on propagationis that it may produce some attenuation at frequencies below 30 GHz. Hitherto,there is no model in order to predict the real effects [38, 33].

Effects of Snow

Snow may have some fading effect on reflector antennas, specially, when thereflector is looking vertically. Dielectric losses of dry snow can be neglected,however, asymmetrically gathered snow can distort the antenna’s beam causingphase delay that can, theoretically, lead to the complete disappearance of thesignal in extreme cases [50, 51]. Nevertheless, this effect can be easily preventedif accumulated snow is removed from time to time from the reflector’s surface.

8.2.4 Free Space Path Loss

The free space loss is the loss produced along the line-of-sight path assumingthat no obstacles are present to produce reflection and/or diffraction. It is themost significant loss of the propagation losses, and it depends on frequency andon the distance between the satellite and the ground station. It is calculated indB, using Equation 8.8 [52, 25].

FSL = 20 log

(

4 · π · dλ

)

(8.8)

47

8.3 Cases Under Study

The actual distance between the satellite and the station depends on the ele-vation angle, increasing as the elevation angle decreases, rising the total losses.

Moreover, the free space path losses are directly proportional to frequency. Asa result, the higher the frequency, the higuer the losses.

8.3 Cases Under Study

In order to evaluate the performance of the ground station, different particularcases are chosen for the missions of the ground station.

For all missions, the propagation losses will be calculated for a minimum ele-vation angle of 5 and a maximum of 90, correponding to the worst and the bestcase, respectively.

The frequencies and the altitudes are fixed for all the missions, except forGENSO, which has to be able to operate in the whole amateur radio S-band. Asa result, for GENSO, propagation losses will be calculated for both 2400 MHzand 2450 MHz.

Moreover, another parameter that can vary in GENSO is the altitude of thesatellite. Educational scientific satellites are commonly situated in LEO, at analtitude range between 600 and 1450 km. A study of the propagation losses willbe carried out for both altitudes.

Thus, a study of the GENSO project will convey the study of 8 different cases(all the possible combinations with altitude, frequency and elevation angle).

8.4 The BRITE Constellation Propagation Losses

In Table 8.2, the results for the propagation losses are shown for the two differentcases under study: 0 and 90 elevation angles.

Table 8.2: Propagation losses for BRITE.

Satellite Altitude km 900 900Elevation Angle degrees 5 90

Distance to Satellite km 900.0 2992.4Propagation Losses dB 169.38 158.51

48

8.5 The GENSO Project Propagation Losses

In Figure 8.4 can be seen how the losses are distributed according to theirorigin, observing, as expected, that the free space loss is the most significant.

BRITE DOWNLINK

168,9

158,47

0,04

0,42

0,004

0,05

0

156

158

160

162

164

166

168

170

172

095 Elevation Angle (degrees)

Lo

ss (

dB

)

Rain Att.

Gas Att.

FSL

Figure 8.4: Distribution of BRITE losses.


In Table 8.3 and Table 8.4, the results for the propagation losses are shown forthe eight different cases under study: the different possible combinations of 0 and90 elevation angles, 600 and 1450 km satellite altitudes, and 2400 and 2450 MHzfrequencies.

There is no difference in the losses between uplink and downlink for the casesselected.

Table 8.3: Propagation losses for GENSO with a satellite altitude of 600 km.

Satellite Altitude km 600Frequency MHz 2400 2450Elev. Angle degrees 5 90 5 90

Satellite Distance km 2328.0 600.0 2328.0 600.0Propagation Loss dB 167.82 155.61 168.00 155.79

49


Table 8.4: Propagation losses for GENSO with a satellite altitude of 1450 km.

Satellite Altitude km 1450Frequency MHz 2400 2450Elev. Angle degrees 5 90 5 90

Satellite Distance km 2328.0 600.0 2328.0 600.0Propagation Loss dB 172.56 163.27 172.74 163.45

Regarding the results, it can be said, as expected, that the best case is for asatellite altitude of 600 km, at frequency 2400 MHz, and with an elevation angleof 90. On the other hand, the worst case is for a satellite altitude of 1450 km,at frequency 2450 MHz, and with an elevation angle of 5.

Propagation Losses for GENSO

155,78767155,60847

167,82250 168,00280

00254,36118272,361

172,55621 172,73653

154,0

156,0

158,0

160,0

162,0

164,0

166,0

168,0

170,0

172,0

174,0

2390 2400 2410 2420 2430 2440 2450 2460

Frequency (MHz)

Pro

pa

ga

tio

n L

os

s (

dB

)

Altitude 600 km - Elev. Angle 90°




Figure 8.5: Propagation Losses for GENSO.

Studying Figure 8.5, the propagation losses increase with distance (altitudeand elevation angle), elevation angle and frequency. However, as can be observedin the results, the dependance on distance is much greater than on frequency, forthe cases under study. The difference in losses between 2400 MHz and 2450 MHzis much less for a certain altitude and elevation angle, than the difference in lossesbetween different distances, for a certain frequency.

50

8.6 The COROT Satellite Propagation Losses

8.6 The COROT Satellite Propagation Losses

In Table 8.5, the results for the propagation losses are shown for the two differentcases under study: 0and 90elevation angles.

Table 8.5: Propagation losses for COROT.

Satellite Altitude km 896 896Elevation Angle degrees 5 90

Distance to Satellite km 896 2984.2Propagation Losses dB 169.54 158.65

8.7 The MOST Project Propagation Losses

In Table 8.6, the results for the propagation losses are shown for the four differentcases under study: 0 and 90 elevation angles, for the uplink and downlinkfrequencies.

Table 8.6: Propagation losses for MOST.

Satellite Altitude km 830Uplink Downlink

Frequency MHz 2055 2232Elevation Angle degrees 5 90 5 90

Distance to Satellite km 2846.7 830.0 2846.7 830.0Propagation Losses dB 168.21 157.08 168.93 157.80

51

Chapter 9

Link Budgets

9.1 Link Budget Calculation

It is important to design a communication system in a way so that its perfor-mance can be predicted prior to its deployment. This is done by means of thelink budget. The link budget is a compilation of all gains and losses along thelink, obtaining, in the end, a link margin [50]. The link margin describes howrobust the link is. A small margin can entail loss of communication in a certainmoment. However, providing a very big link margin is not necessarily a sign ofwell planning, as it can mean an overdesign of the system. Along this chapter,the calculation of link budgets will be described, both for uplink and downlink,and link budgets for the different missions that the ground station supports, willbe shown.

9.1.1 Uplink Budget

For the uplink budget, the situation under study will be the one shown inFigure 9.1.

The uplink budget is a measure of the quality of the signal arriving at thesatellite when the ground station is transmitting. In order to achieve this, a seriesof step calculations need to be done. To begin with, we focus on the transmitter,in this case, our ground station. The HPA will provide an amount of power, Pt,that will decrease by the time it arrives to the antenna feed due to the lossesbetween them, Lt. Once the signal is at the antenna feed, before propagating,this signal will be focused by the antenna. This yields in an improvement, ifcompared to an isotropic radiator, by the antenna gain, Gt. With this data, theEquivalent Isotropically Radiated Power (EIRP) can be calculated. The EIRPserves as a parameter figure of merit for the transmit portion of the link, andcan be calculated in dBm using Equation 9.1, [26, 53, 47].

EIRP (dBm) = Pt (dBm) +Gt (dBi)− Lt (dB) (9.1)

The next step is to calculate the received isotropic power at the satellite. Inorder to do so, first, the total propagation losses need to be known. The total

52


HPA∑ Losses

θ

Gt

Lpointing

Lt Pt

Lpolarization

Gr , TN , BNFSL + ATM

revieceRrettimsnarT

Altitude

Figure 9.1: Uplink budget.

propagation loss is the sum of the free space path loss, LFSL, the atmosphericlosses, LATM , the polarization loss, Lpolarization and, finally, the total pointingloss of the system, Lpointing.

LPROP (dB) = LFSL (dB) + LATM (dB) + Lpolarization (dB) + Lpointing (dB) (9.2)

LFSL and LATM are described in Chapter 8. The polarization loss will be, inworst case, 3 dB, when transmitting with linear polarization and receiving withcircular polarization. This value will be used for the link budget calculations.

On the other hand, the pointing loss is the loss due to the misalignment ofthe transmit and receive antennas. In case of perfect alignment, the maximumgain is achieved. However, as we move away from the perfect angle of alignment,the gain drops significantly [50]. Causes of misalignment are the angle deviationof the rotator, the structure, and the reflector and feed themselves, as well as,misalignment in the satellite antenna. Moreover, the atmosphere can also causevariations in the elevation angle that can cause some pointing loss. Due to themisalignment, the actual gain will decrease, and could be calculated by means ofEquation 9.3, [27].

G = Gt − 12 ∗(

Pointing errorHPBW

)2

(9.3)

53


Resulting in a pointing loss, Lpointing, in dB:

Lpointing = 12 ∗(

Pointing errorHPBW

)2

(9.4)

Where HPBW is described in Chapter 7, and the pointing error is the sum ofall the angles of deviation wih respect to perfect alignment, in degrees.

At this point, the received isotropic power can be easily calculated usingEquation 9.5, [26].

Pri (dBm) = EIRP (dBm)− LPROP (dB) (9.5)

To calculate the received power in the LNA input of the receiver, the gain ofthe satellite’s antenna, Gr, and the losses between the antenna and the LNA, Lr,have to be taken into account.

Pr (dBm) = Pri (dBm) +Gr (dB)− Lr (dB) (9.6)

Another parameter of interest for a link budget is the G/T factor, which isthe ratio between the receiver’s final gain, Gr − Lr, and the receiver’s noisetemperature, Tsys [32]. This noise temperature, will be equal to 2400 K becausethe satellite antenna is pointing towards the “hot” Earth [36, 1].

G

T(dB/K) = Gr (dB)− Lr (dB)− 10 log (Tsys) (dBK) (9.7)

Once, the G/T ratio is known, it is easy to calculate the ratio C/N0 at thereceiver. This ratio is the Carrier-to-Receiver-Noise-Density, with N0 = k · Tsys

and k = 1, 38065× 10−23 J/K (Boltzmann’s Constant), [53, 47].

C

N0

(dBHz) = Pri (dBm) +G

T(dB/K)− 10 log (k) (dB/Ks) + 30 (dB) (9.8)

The ratio C/N is the Carrier-to-Noise ratio, and is one of the most importantparameters of the uplink budget. Unlike the C/N0 ratio, the C/N ratio takesinto account the receiver’s bandwith, B, in Hz. It can be calculated from theC/N0 ratio using Equation 9.9, [53, 47, 26].

C

N(dB) =

C

N0

(dBHz)− 10 log (B) (dBHz) (9.9)

Finally, in order to calculate the link margin, the Eb/No ratio at the receiveris needed. This ratio represents the ratio between the energy per bit and thenoise density [26].

Eb

N0

(dB) =C

N0

− 10 log (R) (9.10)

54


Where, R is the channel data rate in bps (bits per second). This rate willdepend on the code rate and the information data rate. The code rate or efficiencyof a Forward Error Correction (FEC) code, such as a convolutional code, can beexpressed as a fractional number, k/n, meaning that, once the information isencoded, a n-bit codeword for every k-bit dataword will be produced [47]. Inother words, for every k bits of information, n bits will be generated, wherek < n. Therefore, k − n bits will be redundant, and the bandwidth will beexpanded by a factor of n/k.

Despite not having fixed code rates, typically for convolutional codes, coderates of 1/2, 2/3, 3/4, etc, are used. For the following calculations, a code rateof 1/2 will be assumed.

In summary, if, for instance the information data rate is Rinfo and the coderate is 1/2, then the channel data rate, R, will result in Rinfo

1/2.

Lastly, the required Eb

N0for a certain Bit Error Rate (BER), is needed. It will

depend on the modulation, the required BER and the coding gain. The codinggain is defined as the difference in dB, for a certain value of BER, between theEb

N0without coding, that is, assuming a code rate of 1, and with coding, assuming

a code rate different to 1, both having the same information bit rate. Table 9.1shows the required Eb

N0for a BER of 10−6 and coding gain for a BPSK modulation

scheme, with different code rates [27, 47].

Table 9.1: Theoretical required Eb

N0for a BER of 10−6 and coding gain for BPSK

modulation using different code rates.

Code Rate Required Eb

N0Coding Gain

1 10.5 dB 0 dB7/8 6.9 dB 3.6 dB3/4 5.9 dB 4.6 dB2/3 5.5 dB 5 dB1/2 5 dB 5.5 dB

The link margin will finally be:

LinkMargin (dB) = Required Eb/N0 (dB)− Calculated Eb/N0 (dB) (9.11)

9.1.2 Downlink Budget

For the downlink budget, a similar procedure is carried out. This time, theground station is receiving the signal from the satellite. Therefore, the EIRP willnow be provided by the satellite, and the ground station should now present theleast noise temperature possible in order to achieve a good Eb

N0ratio.

55


LNA∑ Losses

θ

Gt,

Lpointing

Lt,

Pr

Lpolarization

Gr , TN , BN

FSL + ATM

TransmitterReceiver

Lr

Pt

Altitude

Figure 9.2: Downlink budget.

For the downlink, the situation under study is as it is shown in Figure 9.2.The steps to follow in order to calculate the link margin are the same as in the

uplink budget, but this time, taking into account that the receiver is the groundstation, and the transmitter is the satellite.

Nevertheless, for the downlink, the noise temperature of the ground stationneeds to be calculated.

Downlink Noise Temperature

The noise present in the ground station is modelled as thermal noise. The noisetemperature, measured in Kelvin, defines the sensitivity of the receiver. Both theantenna and the receiver are contributing to the overall noise of the system. Thesystem’s total noise temperature is calculated as indicated in Equation 9.12 [25].

Tsys = TA + Trec (9.12)

Where, TA is the antenna’s noise temperature, and Trec is the receiver’s noisetemperature, both measured in K.

There are two main contributors to the antenna noise: noise from the physicalstructure of the antenna due to its losses, and noise from the radio path (alsoknown as sky noise) [26].

56


Usually, the antenna losses are already included in the antenna’s apertureefficiency, therefore, there is no need to include them at this point.

Regarding the sky noise, this noise can come from both natural and humansources, and it is affected by galactic and extraterrestrial noise, as well as byatmospheric events [26].

The total antenna noise temperature can be calculated using Equation 9.13[27].

TA = Tsky · 10−A/10 + Tm ·(

1− 10−A/10)

+ Tfeed + Tground (9.13)

Where,

Tm is the average temperature of rain. A value between 260 and 280 K is typicallyused (I will use 280 K in calculations), [27, 54].

A is the rain and gas attenuation in dB.

Tfeed is the noise temperature of the feed.

Tground is the temperature of the ground, that is reflected into the antenna. Itsvalue is 50 K for elevation angles between 0 and 10, and 10 K for elevationangles between 10 and 90.

Tsky is the temperature of the cold sky. According to the ITU recommendationsand other publications [55], this temperature is 20 K for an elevation angleof 5, and 2 K if the elevation angle is 90.

On the other hand, the receiver’s equivalent noise temperature in K is calcu-lated using Equation 9.14, [47, 26].

Trec = T1 +T2

G1

+T3

G1 ·G2

+T4

G1 ·G2 ·G3

+ . . . (9.14)

Ti are the different noise temperatures of the components in the receivingpipeline, as shown in Figure 9.3, and Gi represents the gain (loss, if less than 1)of the component.

The components were put into groups so that in each box there were either oneactive component or one or more passive components, but not a mixture. Thereason to do that is that the noise temperature is obtained slightly differently forpassive and for active components [26].

The equivalent noise temperature of a component is calculated as stated inEquation 9.15 [55, 26].

Ti = T0 (nf − 1) (9.15)

Where T0 is the reference temperature, 290 K, and nf is the noise factor of thecomponent. Usually, the noise figure, NF, is given for the active components,

57


- Cables

- Switch(es)

- Connectors

- Filter/Duplex

Filter

LNA

- Cables

- Connectors

- Polarization

Recovery

Unit

Down

converter

Reference Point

To antenna

T1 T2 T3 T4

Figure 9.3: Downlink budget.

which is just the noise factor expressed in dB. Moreover, for passive components,the noise figure is equal to the insertion loss.

In turn, the noise factor can be easily calculated for the passive componentsas expressed in Equation 9.16

nf = 10NF/10 = 10 Insertion Loss (dB)/10 (9.16)

As can be concluded from Equation 9.14, the further we go from the referencepoint, the less contribution it will have to the total receiver’s noise temperature.As a result, in calculations, only the components until the downconverter aretaken into account.

58

9.2 The BRITE Constellation Link Budget

9.2 The BRITE Constellation Link Budget

Table 9.2 shows the downlink budget for the BRITE Constellation mission. ABPSK modulation scheme with code rate 1/2 will be used, so therefore, therequired Eb

N0value used for the calculations will be 5.12 dB for the downlink [56].

This value for the downlink is given in the specifications of the modem and it isvery similar to the theoretical value given in Table 9.1.

9.3 The GENSO Project Link Budget

For the GENSO Project, Table 9.3, Table 9.4, Table 9.5 and Table 9.6 summarizethe uplink and downlink budgets, for the different cases under study. A BFSKmodulation scheme will be assumed, as well as a information data rate of 9600 bps,as mentioned in Section 5.4. For this modulation scheme, a required Eb

N0of 13.1 dB

is necessary [57].

9.4 The COROT Satellite Link Budget

Table 9.7 shows the downlink budget for the COROT satellite. The COROTsatellite will use a QPSK modulation scheme for its downlink. Consequently,a required Eb

N0value of 5.12 dB is used in the calculations, as expressed in the

modem’s specifications [56].

9.5 The MOST Project Link Budget

For the MOST Project, Table 9.8 and Table 9.9 show the uplink and downlinkbudgets, respectively. Regarding the modulation used for the downlink, BPSK,the required Eb

N0value used for the calculations will be 5.12 dB [56]. For the

uplink, a value of 5 dB is used for the GFSK modulation scheme [1]. This valueis dependent on the satellite receiver.

59


Table 9.2: Downlink budget for the BRITE Constellation mission.

DownlinkDownlink Frequency 2200 MHzSatellite Altitude 900 kmElevation Angle 5 90

Distance to Satellite 2992.4 km 900 kmSatellite Antenna Gain 0 dBiSatellite Losses 5 dBTransmit Power 26.99 dBmTransmit EIRP 21.99 dBmFSL & Atmospheric Loss 168.72 dB 158.51 dBPointing Error 1.48 1.30

Pointing Loss 1.65 dB 1.27 dBPolarization Mismatch 3 dB 3 dBTotal Propagation Loss 173.37 dB 162.78 dBAntenna Diameter 3.65 mAntenna Efficiency 55%Antenna Gain 36.03 dBiAntenna Beamwidth 3.997

Receiver Line Losses 3 dBSystem Noise Temperature 280.48 K 198.20 KGround Station G/T 11.55 dB/K 13.06 dB/KReceiver Bandwidth 64 kHzReceived Isotropic Power −151.38 dBm −140.80 dBmReceived Power −118.34 dBm −107.76 dBmReceiver Noise Power −126.06 dBm −127.57 dBmC/No 58.77 dBHz 70.87 dBHzC/N 10.71 dB 22.80 dBModulation scheme BPSKInformation Data Rate 32 kbpsCode Rate 1/2Channel Data Rate 64 kbpsCoding Gain 3.01 dBEb/No without coding 13.72 dB 25.81 dBEb/No coded 10.71 dB 22.80 dBEb/No Required for 10−6 5.12 dB 5.12 dBDownlink Margin 5.59 dB 17.68 dB

60


Table 9.3: Uplink budget for the GENSO Project with a satellite altitude of600 km.

UplinkSatellite Altitude 600 kmUplink Freq. 2400 MHz 2450 MHzElevation Angle 5 90 5 90

Distance to Satellite 2328.05 km 600.00 km 2328.05 km 600.00 kmAntenna Diameter 3.65 mAntenna Efficiency 55%Antenna Gain 36.65 dBi 36.83 dBiAntenna Beamwidth 3.997

FSL & Atmo. Loss 167.82 dB 155.61 dB 168.00 dB 155.79 dBPointing Error 1.48 1.30 1.48 1.30

Pointing Loss 1.65 dB 1.27 dB 1.65 dB 1.27 dBPolarization Loss 3 dB 3 dB 3 dB 3 dBTotal Propag. Loss 172.47 dB 159.88 dB 172.65 dB 160.06 dBTransmit Power 46.99 dBmLine Loss 3 dBTransmit EIRP 80.64 dBm 80.82 dBmNoise Temp. 2400 KReceiver Bandwidth 110 kHzSat. Antenna Gain 0 dBiSatellite Losses −3.5 dBSatellite G/T −37.30 dB/KRec. Isotropic Power −91.82 dBm −79.24 dBm −91.82 dBm −79.24 dBmReceived Power −95.32 dBm −82.74 dBm −95.33 dBm −82.74 dBmRec. Noise Power -114.38 dBmC/No 69.47 dBHz 82.06 dBHz 69.47 dBHz 82.06 dBHzC/N 19.06 dB 31.64 dB 19.06 dB 31.64 dBInfo. Data Rate 9.6 kbpsCode Rate 1Channel Data Rate 9.6 kbpsEb/No 29.65 dB 42.24 dB 29.65 dB 42.24 dBEb/No Req. for 10−5 13.4 dBUplink Margin 16.25 dB 28.84 dB 16.25 dB 28.84 dB

61


Table 9.4: Uplink budget for the GENSO Project with a satellite altitude of1450 km.

UplinkSatellite Altitude 1450 kmUplink Freq. 2400 MHz 2450 MHzElevation Angle 5 90 5 90

Distance to Satellite 4014.93 km 1450.00 km 4014.93 km 1450.00 kmAntenna Diameter 3.65 mAntenna Efficiency 55%Antenna Gain 36.65 dBi 36.83 dBiAntenna Beamwidth 3.997

FSL & Atmo. Loss 172.56 dB 163.27 dB 172.74 dB 163.45 dBPointing Error 1.48 1.30 1.48 1.30

Pointing Loss 1.65 dB 1.27 dB 1.65 dB 1.27 dBPolarization Loss 3 dB 3 dB 3 dB 3 dBTotal Propag. Loss 177.20 dB 167.55 dB 177.38 dB 167.73 dBTransmit Power 46.99 dBmLine Loss 3 dBTransmit EIRP 80.64 dBm 80.82 dBmNoise Temp. 2400 KReceiver Bandwidth 110 kHzSatellite Antenna Gain 0 dBiSatellite Losses −3.5 dBSatellite G/T −37.30 dB/KRec. Isotropic Power −96.56 dBm −86.90 dBm −96.56 dBm −86.90 dBmReceived Power −100.06 dBm −90.40 dBm −100.06 dBm −90.40 dBmRec. Noise Power -114.38 dBmC/No 64.74 dBHz 74.39 dBHz 64.74 dBHz 74.39 dBHzC/N 14.33 dB 23.98 dB 14.32 dB 23.98 dBInfo. Data Rate 9.6 kbpsCode Rate 1Channel Data Rate 9.6 kbpsEb/No 24.92 dB 34.57 dB 24.91 dB 34.57 dBEb/No Req. for 10−5 13.4 dBUplink Margin 11.52 dB 21.17 dB 11.51 dB 21.17 dB

62


Table 9.5: Downlink budget for the GENSO Project with a satellite altitude of600 km.

DownlinkSatellite Altitude 600 kmDownlink Freq. 2400 MHz 2450 MHzElevation Angle 5 90 5 90

Distance to Satellite 2328.05 km 600.00 km 2328.05 km 600.00 kmSat Antenna Gain 0 dBiSatellite Losses 3 dBTransmit Power 26.99 dBmTransmit EIRP 24.99 dBmFSL & Atm. Loss 167.82 dB 155.61 dB 168.00 dB 155.79 dBPointing Error 1.48 1.30 1.48 1.30

Pointing Loss 1.65 dB 1.27 dB 1.65 dB 1.27 dBPolarization Loss 3 dB 3 dB 3 dB 3 dBTotal Propag. Loss 172.47 dB 159.88 dB 172.65 dB 160.06 dBAntenna Diameter 3.65 mAntenna Efficiency 55%Antenna Gain 36.65 dBi 36.83 dBiAntenna Beamwidth 3.997

Receiver Line Losses 3 dBNoise Temperature 436.59 K 372.16 K 436.59 K 372.16 KGround Station G/T 10.25 dB/K 10.94 dB/K 10.43 dB/K 11.12 dB/KReceiver Bandwidth 9.6 kHzRec. Isotropic Power −148.48 dBm −135.89 dBm −148.66 dBm −136.07 dBmReceived Power −114.82 dBm −102.24 dBm −114.83 dBm −102.24 dBmRec. Noise Power −132.38 dBm −133.07 dBm −132.38 dBm −133.07 dBmC/No 60.37 dBHz 73.65 dBHz 60.37 dBHz 73.65 dBHzC/N 20.55 dB 33.83 dB 50.55 dB 33.83 dBModulation scheme BFSKInfo. Data Rate 9.6 kbpsCode Rate 1Channel Data Rate 9.6 kbpsCoding Gain 0.00 dBEb/No not coded 20.55 dB 33.83 dB 20.55 dB 33.83 dBEb/No coded 20.55 dB 33.83 dB 20.55 dB 33.83 dBEb/No Req. for 10−6 13.4 dBDownlink Margin 7.15 dB 20.43 dB 7.15 dB 20.43 dB

63


Table 9.6: Downlink budget for the GENSO Project with a satellite altitude of1450 km.

DownlinkSatellite Altitude 1450 kmDownlink Freq. 2400 MHz 2450 MHzElevation Angle 5 90 5 90

Distance to Satellite 4014.93 km 1450.00 km 4014.93 km 1450.00 kmSat Antenna Gain 0 dBiSatellite Losses 3 dBTransmit Power 26.99 dBmTransmit EIRP 23.99 dBmFSL & Atm. Loss 172.56 dB 163.27 dB 172.74 dB 163.45 dBPointing Error 1.48 1.30 1.48 1.30

Pointing Loss 1.65 dB 1.27 dB 1.65 dB 1.27 dBPolarization Loss 3 dB 3 dB 3 dB 3 dBTotal Propag. Loss 177.20 dB 167.55 dB 177.38 dB 167.73 dBAntenna Diameter 3.65 mAntenna Efficiency 55%Antenna Gain 36.65 dBi 36.83 dBiAntenna Beamwidth 3.997

Receiver Line Losses 3 dBNoise Temperature 436.59 K 372.16 K 436.66 K 372.17 KGround Station G/T 10.25 dB/K 10.94 dB/K 10.43 dB/K 11.12 dB/KReceiver Bandwidth 9.6 kHzRec. Isotropic Power −153.21 dBm −143.56 dBm −153.39 dBm −143.74 dBmReceived Power −119.56 dBm −109.90 dBm −119.56 dBm −109.90 dBmRec. Noise Power −132.38 dBm −133.07 dBm −132.38 dBm −133.07 dBmC/No 55.64 dBHz 65.99 dBHz 55.64 dBHz 65.99 dBHzC/N 15.82 dB 26.16 dB 15.81 dB 26.16 dBModulation scheme BFSKInfo. Data Rate 9.6 kbpsCode Rate 1Channel Data Rate 9.6 kbpsCoding Gain 0.00 dBEb/No not coded 15.81 dB 26.16 dB 15.80 dB 26.16 dBEb/No coded 15.81 dB 26.16 dB 15.80 dB 26.16 dBEb/No Req. for 10−6 13.4 dBDownlink Margin 2.41 dB 12.76 dB 2.40 dB 12.76 dB

64


Table 9.7: Downlink budget for the COROT satellite.


Distance to Satellite 2984.2 km 896.00 kmSatellite Antenna Gain 0 dBiSatellite Losses 0 dBTransmit Power 37.67 dBmTransmit EIRP 37.67 dBmFSL & Atmospheric Loss 168.88 dB 158.65 dBPointing Error 1.48 1.30


Receiver Line Losses 3 dBSystem Noise Temperature 280.32 K 198.21 KGround Station G/T 12.56 dB/K 14.06 dB/KReceiver Bandwidth 2000 kHzReceived Isotropic Power −135.86 dBm −125.26 dBmReceived Power −101.82 dBm −91.22 dBmReceiver Noise Power −111.11 dBm −112.62 dBmC/No 75.30 dBHz 87.40 dBHzC/N 12.29 dB 24.39 dBModulation scheme QPSKInformation Data Rate 420 kbpsCode Rate 1/2Channel Data Rate 840 kbpsCoding Gain 3.01 dBEb/No without coding 19.08 dB 31.18 dBEb/No coded 16.07 dB 28.17 dBEb/No Required for 10−6 5.12 dB 5.12 dBDownlink Margin 10.95 dB 23.05 dB

65


Table 9.8: Uplink budget for the MOST Project.

UplinkUplink Frequency 2055 MHzSatellite Altitude 830 kmElevation Angle 5 90

Distance to Satellite 2846.65 km 830.00 kmAntenna Diameter 3.65 mAntenna Efficiency 55%Antenna Gain 35.31 dBiAntenna Beamwidth 3.997

FSL & Atmospheric Loss 168.21 dB 157.08 dBPointing Error 1.48 1.30

Pointing Loss 1.65 dB 1.27 dBPolarization Mismatch 3 dB 3 dBTotal Propagation Loss 172.86 dB 161.35 dBTransmit Power 46.99 dBmLine Loss 3 dBTransmit EIRP 79.30 dBmSystem Noise Temperature 2400 KReceiver Bandwidth 110 kHzSatellite Antenna Gain 0 dBiSatellite Losses 2 dBSatellite G/T −35.80 dB/KReceived Isotropic Power −93.56 dBm −82.06 dBmReceived Power −95.56 dBm −84.06 dBmReceiver Noise Power -114.38 dBmC/No 69.23625 dBHz 80.74 dBHzC/N 18.82232 dB 30.33 dBModulation scheme GFSKInformation Data Rate 9.6 kbpsCode Rate 1/2Channel Data Rate 19.2 kbpsEb/No 26.40 dB 37.91 dBEb/No Required for 10−5 5 dB 5 dBUplink Margin 21.40 dB 32.91 dB

66


Table 9.9: Downlink budget for the MOST Project.


Distance to Satellite 2846.65 km 830.00 kmSatellite Antenna Gain 0 dBiSatellite Losses 2 dBTransmit Power 26.99 dBmTransmit EIRP 24.99 dBmFSL & Atmospheric Loss 167.55 dB 157.08 dBPointing Error 1.48 1.30


Receiver Line Losses 3 dBSystem Noise Temperature 280.24 K 198.20 KGround Station G/T −35.80 dB/KReceiver Bandwidth 110 kHzReceived Isotropic Power −147.21 dBm −136.36 dBmReceived Power −114.19 dBm −103.34 dBmReceiver Noise Power −123.71 dBm −125.21 dBmC/No 62.94 dBHz 75.29 dBHzC/N 12.52 dB 24.88 dBModulation scheme BPSKInformation Data Rate 38.4 kbpsCode Rate 1/2Channel Data Rate 76.8 kbpsCoding Gain 3.01 dBEb/No without coding 17.09 dB 29.45 dBEb/No coded 14.08 dB 26.44 dBEb/No Required for 10−6 5.12 dB 5.12 dBDownlink Margin 8.96 dB 21.31 dB

67

9.6 Conclusion

9.6 Conclusion

The link budgets show a really good theoretical performance of the ground sta-tion. The margins are sometimes big, allowing the use of, in case of the uplink,HPAs with lower gains if necessary. In case of the downlink, big margins are ob-tained for some missions in the interest of other missions, so that all can receivewith enough margin, assuring communication.

9.7 Intermodulation and Interference

At the ground station’s operating frequencies, there is plenty of interfering sys-tems, such as Universal Mobile Telecommunications System (UMTS)1, as well asmost of the wireless personal area networks such as bluetooth or IEEE 802.11devices, which are designed to work in the 2.4 GHz ISM band. Furthermore,most 3G networks in Europe operate in the 2100 MHz frequency band. Robustprotocols, modulation and codification schemes are used in order to counteractthe strong interference. Moreover, these intefering frequencies may degrade oursignal and also cause intermodulation. The duplex filter in front of the LNAfor the scientific frequency band, the filter for GENSO receiving pipeline, andthe filters after the HPAs in both bands, will avoid most of the serious inter-modulation in the station. What is more, the active elements like the LNA andthe downconverters can generate intermodulation products themselves that arefiltered later in the chain.

1UMTS will use the bands of 1885-2025MHz and 2110-2200MHz for the IMT-2000 systemsand, precisely, the bands 1980-2010MHz and 2170-2200MHz for the satellite services ofthese systems

68

Chapter 10

Summary

To sum up, the future ground station of the Institute of Communications andRadio-Frequency Engineering of Viena University of Technology, that will belocated on the roof of the Electrical Engineering Faculty building, will, accordingto the results of the link budgets, have a very good performance for elevationangles as low as 4 degrees, providing sufficient link margins to make up for someunpredicted losses. For elevation angles below 5 degrees, as explained in thisthesis, losses are much greater, and communications might be held most of thetimes, but cannot be assured. Moreover, it can be seen that, within the frequencyrange of the ground station’s S-band front-end, the total propagation loss willnot change significantly, whilst, changing the distance between the ground stationand the satellite, which is given by the elevation angle, can suppose an increaseof up to 10 dB in the losses for the missions considered.

The ground station is able to support different missions, at different frequencybands, at different distances, with different transmitted powers, therefore, insome cases, the margins have to be big. This is necessary in order to provideevery mission or project, sharing components within the receiving pipeline, withenough margin to assure communication.

69

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[39] ITU-R Rec. P.834-6, Effects of Tropospheric Refraction on Radiowave Pro-pagation.

[40] ITU-R Rec. P.453-9, The Radio Refractive Index: Its formula and refractivitydata.

[41] ITU-R Rec. P.676-7, Attenuation by Atmospheric Gases.[42] ITU-R Rec. P.1510, Annual Mean Surface Temperature.[43] ITU-R Rec. P.619-1, Propagation Data required for the Evaluation of Inter-

ference between Stations in Space and those on the Surface of the Earth.[44] ITU-R Rec. P.837-5, Characteristics of Precipitation for Propagation Mo-

delling.[45] ITU-R Rec. P.839-3, Rain Height Model for Prediction Methods.[46] ITU-R Rec. P.838-3, Specific Attenuation Model for Rain for use in Predic-

tion Methods.[47] Tirró S., Satellite Communications Systems Design, Plenum Press, Rome,

1993.[48] ITU-R Rec. P.840-3, Attenuation due to Clouds and Fog.[49] Barue G., Microwave Engineering. Land & Space Radiocommunications,

John Wiley & Sons, New York, 2008.[50] Seybold John S., Introduction to RF Propagation, John Wiley & Sons, New

Jersey, 2005.[51] Salonen E., Attenuation Phenomena on Earth Satellite Links, McGraw Hill,

Helsinki University of Technology, 1992.[52] ITU-R Rec. P.525-2, calculation of Free-Space Attenuation.[53] Gagliardi, Robert M., Satellite Communications, 2nd Edition, Van Nostrand

Reinhold, California, 1991.

A.3

Bibliography

[54] ITU-R Rec. P.372-9, Radio Noise.[55] Pozar David M., Microwave Engineering, 3rd Edition, John Wiley & Sons,

Massachusetts, 2005.[56] Datum Systems, PSM-500 Modem Manual, Appendix A Specifications, Rev

0.86, April 2008.[57] Sklar B., Digital Communications. Fundamentals and Applications, 2nd Edi-

tion, Prentice Hall, California, 2001.

A.4

List of Abbreviations

LEO Low Earth OrbitVHF Very High FrequencyUHF Ultra High FrequencyRHCP Right Hand Circular PolarizationLHCP Left Hand Circular PolarizationLNA Low Noise AmplifierHPA High Power AmplifierBRITE BRIght Target ExplorerHPBW Half Power Beam WidthRF Radio FrequencyIF Intermediate FrequencyLO Local Oscillatormodem modulator-demodulatorTNC Terminal Node ControllerHDLC High-level Data Link ControlPC Personal ComputerSMA SubMiniature version AMOST Microvariability and Oscillations of STarsSFL Space Flight LaboratoryACS Attitude Control SystemCSA Canadian Space AgencySNR Signal to Noise RatioGNB Generic Nanosatellite BusADC Attitude Determination and ControlGMSK Gaussian Minimum Shift KeyingBPSK Binary Phase Shift KeyingCOROT COnvection ROtation and planetary TransitsESA European Space AgencyGENSO Global Educational Network for Satellite OperatorsISEB International Space Education BoardAUS AUthentication ServerGSS Ground Station ServerMCC Mission Control ClientFSK Frequency Shift KeyingFM Frequency ModulationQPSK Quadrature Phase Shift KeyingSNR Signal to Noise Ratio

B.1

Acronyms

PE PolyEthyleneTEC Total Electron ContentXPD Cross-Polarization DiscriminationITU International Telecommunication UnionEIRP Equivalent Isotropically Radiated PowerFEC Forward Error CorrectionBER Bit Error RateUMTS Universal Mobile Telecommunications SystemCNES Centre National d’Études SpatialesPSL Participating Spacecraft ListIF Intermediate Frequency

B.2

List of Figures

2.1 The MOST Satellite, [2] . . . . . . . . . . . . . . . . . . . . . . . 3

3.1 COROT Satellite. [5] . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.1 The number of stars to +3.5 magnitude in 25 degrees of field viewfor BRITE. [6] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.2 Structure of a BRITE Satellite. [12] . . . . . . . . . . . . . . . . . 104.3 Attitude control hardware of the BRITE satellite. [8] . . . . . . . 114.4 Patch antennas mounted on the BRITE satellites. [12] . . . . . . 124.5 Components of the GNB BRITE satellite. [12] . . . . . . . . . . . 13

5.1 Components of a GENSO network. . . . . . . . . . . . . . . . . . 175.2 Diagram of a standard GENSO ground station. . . . . . . . . . . 175.3 AMSAT-OSCAR 51 (Echo AO-51) microsatellite. [19] . . . . . . . 18

6.1 Division of a ground station into three segments. . . . . . . . . . . . . 226.2 Overview of the three segments of a ground station. . . . . . . . . . . 226.3 A closer look into the three segments. . . . . . . . . . . . . . . . . . 236.4 Other subsystems of a ground station. . . . . . . . . . . . . . . . . . 246.5 Ground Station S-Band Outline. . . . . . . . . . . . . . . . . . . . . 266.6 Ground station S-band diagram. . . . . . . . . . . . . . . . . . . . . 28

7.1 Losses due to spillover. . . . . . . . . . . . . . . . . . . . . . . . . . 307.2 The duplex filter of our ground station. . . . . . . . . . . . . . . . . 327.3 A fixed-frequency converter used in Earth Stations. . . . . . . . . . . 36

8.1 Faraday Rotation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 428.2 Range Delay and Time Excess. . . . . . . . . . . . . . . . . . . . 438.3 Dispersion and Phase Advance. . . . . . . . . . . . . . . . . . . . 448.4 Distribution of BRITE losses. . . . . . . . . . . . . . . . . . . . . 498.5 Propagation Losses for GENSO. . . . . . . . . . . . . . . . . . . . 50

9.1 Uplink budget. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539.2 Downlink budget. . . . . . . . . . . . . . . . . . . . . . . . . . . . 569.3 Downlink budget. . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

B.1 Refraction and fading of our ground station at 2.4 GHz . . . . . . Ap.5

C.1

List of Tables

2.1 Frequency and data rates of the MOST satellite. . . . . . . . . . . 3

3.1 Summary of the main characteristics of the COROT satellite. . . 6

4.1 Summary of the main characteristics of the BRITE satellites. . . . 14

5.1 Classification of small satellites. . . . . . . . . . . . . . . . . . . . 185.2 Common amateur satellite frequency allocations. . . . . . . . . . . 195.3 Common amateur satellite modes. . . . . . . . . . . . . . . . . . . 19

6.1 Scientific bands and frequencies of interest for the ground station. 236.2 Frequencies of the satellite missions considered. . . . . . . . . . . 256.3 Frequencies in the S-Band. . . . . . . . . . . . . . . . . . . . . . . 25

7.1 Duplex filter selected. . . . . . . . . . . . . . . . . . . . . . . . . . 327.2 Typical LNA values. . . . . . . . . . . . . . . . . . . . . . . . . . 337.3 GENSO selected LNA. . . . . . . . . . . . . . . . . . . . . . . . . 337.4 Scientific band selected LNA. . . . . . . . . . . . . . . . . . . . . 347.5 Selected filters for the ground station. . . . . . . . . . . . . . . . . 347.6 Selected HPAs for the ground station. . . . . . . . . . . . . . . . . 357.7 Datum Systems PSM500 satellite modem specifications. . . . . . . 377.8 Typical attenuation values for cables. . . . . . . . . . . . . . . . . 387.9 Specifications of cables used in the ground station. . . . . . . . . . 38

8.1 Classification of Propagation Effects. . . . . . . . . . . . . . . . . 408.2 Propagation losses for BRITE. . . . . . . . . . . . . . . . . . . . . 488.3 Propagation losses for GENSO with a satellite altitude of 600 km. 498.4 Propagation losses for GENSO with a satellite altitude of 1450 km. 508.5 Propagation losses for COROT. . . . . . . . . . . . . . . . . . . . 518.6 Propagation losses for MOST. . . . . . . . . . . . . . . . . . . . . 51

9.1 Theoretical required Eb

N0for a BER of 10−6 and coding gain for

BPSK modulation using different code rates. . . . . . . . . . . . . 559.2 Downlink budget for the BRITE Constellation mission. . . . . . . 609.3 Uplink budget for the GENSO Project with a satellite altitude of

600 km. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619.4 Uplink budget for the GENSO Project with a satellite altitude of

1450 km. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

D.1

List of Tables

9.5 Downlink budget for the GENSO Project with a satellite altitudeof 600 km. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

9.6 Downlink budget for the GENSO Project with a satellite altitudeof 1450 km. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

9.7 Downlink budget for the COROT satellite. . . . . . . . . . . . . . 659.8 Uplink budget for the MOST Project. . . . . . . . . . . . . . . . . 669.9 Downlink budget for the MOST Project. . . . . . . . . . . . . . . 67

A.1 Beam spread loss for Vienna’s Institute of Communications andRadio-Frequency Engineering ground station. . . . . . . . . . . . Ap.1

C.1 Defocusing Loss for Vienna’s Institute of Communications andRadio-Frequency Engineering ground station. . . . . . . . . . . . Ap.6

D.1 Gaseous attenuation parameters of our ground station at 2.4 GHz. Ap.10D.2 Gaseous attenuation of our ground station at 2.4 GHz. . . . . . . Ap.10

E.1 Parameters used to calculate the rain attenuation for our groundstation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ap.13

E.2 Rain attenuation of our ground station. . . . . . . . . . . . . . . . Ap.13

D.2

Appendix A

Beam Spreading Loss using the

ITU Model

The beam spreading loss depends only on the apparent elevation angle θ, whichcan, in turn, be calculated from the elevation angle and the ground station’saltitude above sea level [38].

Abs = 2.27− 1.16 log(1 + θ) (A.1)

Where θ is the apparent elevation angle in mrad.In order to calculate θ, the station’s altitude above sea level, hs, and the

elevation angle, θ0, are needed.

θ = θ0 + τs(hs, θ0) (A.2)

where τs is

τs(hs, θ0) = 1/[1.728 + 0.5411 θ0 + 0.03723 θ02 + hs (0.1815 + 0.06272 θ0+

+ 0.01380 θ20) + h2s (0.01727 + 0.008288 θ0)],

(A.3)

checking previously if the station is visible.In the case of our ground station, where hs = 205m, the values obtained are

shown in Table A.1.

Table A.1: Beam spread loss for Vienna’s Institute of Communications andRadio-Frequency Engineering ground station.

Elevation Angle degrees 0.1 1 2

τs 0.54892 0.42368 0.32951

Apparent Elevation Angledegrees 0.64892 1.42368 2.32951

mrad 11.32577 24.84782 40.65767Abs dB 1.00466 0.63159 0.39115

Ap.1

Appendix B

Refraction and Fading using the

ITU Model

Deep Fading

STEP 1 Obtain the apparent elevation angle θ in mrad. This is already ex-plained in Appendix A for the beam spreading loss.

STEP 2 Obtain the geoclimate factor, Kw, for the path location.

Kw = 100.1 (C0 + CLat) ρL1.5 (B.1)

Where:C0 = 76 according to Table 3 in the ITU Recommendation 618-8 [38].CLat = 0 regarding the ground station’s latitude. ρL needs to be calculatedby means of ITU Recommendation 453 [40]. From the maps containedin this recommendation, the percentage of time that the refraction indexgradient is equal or less than −100 units N/km in different times of theyear, can be obtained:– February: 1%– May: 5%– August: 5%– November: 5%

The highest value is 5%Therefore, ρL = 0.05.

STEP 3 Finally, the loss, Aref can be calculated using Equation B.2.

Aref (dB) = Gw + 92 + 9 log f − 55 log(1 + θ0)− 10 log p (B.2)

Where:

Gw (dB) = 10 logKw − 92 (B.3)

Ap.2

Appendices

f is the frequency in Hz, p is the percentage of time that fade depth isexceeded in the worst month, and θ0 is the apparent elevation angle.

STEP 4 Calculation of the percentage of time that the fade depth, Aref , isexceeded in the average year. In order to calculate this, Equation B.4 isused.

p = Kaf0.9(1 + θ0)

−5.5 × 10−Aref/10 [%] (B.4)

Where:

Ka = Kw × 10−0.1∆G [%] (B.5)

and

∆G = −1.8− 5.6 log(1.1± |cos 2Ψ|0.7)+ 4.5 log(1 + θ0)

(B.6)

For latitudes above 45 the minus sign is used in Equation B.6.In Figure B.1, sample calculations are done at frequency 2.4 GHz.

Shallow Fading

STEP 1 Estimation of Aref exceeded for 63% of the average worst month oraverage year, A63.Due to the latitude of the ground station, A63 coincides with the attenua-tion, Abs calculated for the beam spread loss in Appendix A.

STEP 2 Calculation of the percentage of time, pt, that the fade depth of At = 25dB is exceeded.

pt = Kwf0.9(1 + θ0)

−5.5 × 10−Aref/10 [%] (B.7)

STEP 3 Calculation of the new percentage of time, p, from:

p = 10−0.1A63+log pt [%] (B.8)

STEP 4 Calculation of parameter q′.

q′ = −20

At

log[− ln(100− p

100)] (B.9)

Ap.3

Appendices

STEP 5 Calculation of the values of the shape factor, qt.

qt = (q′ − 2)/[(1 + 0.3× 10−At/20)× 10−0.016At ]−− s0(10

−At/20 + At/800)(B.10)

Where:

s0 = −1.6− 3.2 log f + 4.2 log (1 + θ0) (B.11)

f , is the frequency expressed in GHz, and θ0 is the elevation angle in mrad.

STEP 6 In case qt was negative, the previous steps should be repeated forAt = 35 dB.This is not the case for our ground station.

STEP 7 There are two different cases:If Aref ∈ [A63, A63 + At], p and q are calculated using the following formu-las:

p = 100[

1− exp(

−10−q(Aref−A63)/20)]

(B.12)

q = 2 + 10−0.016(Aref−A63)[

1 + 0.3× 10−(Aref−A63)/20]

··[

qt + s0(

10−(Aref−A63)/20 + (Aref − A63)/800)] (B.13)

These formulas were used, in the calculations for our ground station, for anelevation angle of 1.If Aref > A63 + At, p is calculated using Equation B.7. This was used inthe case of elevation angles of 0.1 and 0.5.

STEP 8 Finally, there is a last step if Aref < A63. However, this was not thecase so it will not be described here. For further information, go to theITU-R recommendation 618-8 [38].

Ap.4

Appendices

Figure B.1: Refraction and fading of our ground station at 2.4 GHz .

Ap.5

Appendix C

Focusing and Defocusing using the

ITU Model

This effect can be calculated for elevation angles less than 10 but should beneglected for angles greater than 3.

The total attenuation due to refraction in the atmosphere, in dB, can be cal-culated using Equation C.1 [39].

b = ±10 log (B) (C.1)

Where,

B = 1− 0.5411 + 0.07446 · θ0 + h (0.06272 + 0.0276 · θ0) + h2 · 0.08288[

1.728 + 0.5411 · θ0 + 0.03723 · θ02 + h · x+ h2 · y]

2

(C.2)

x = 0.1815 + 0.06272 · θ0 + 0.0138 · θ02 (C.3)

y = 0.01727 + 0.008288 · θ0 (C.4)

In Equation C.1, we will use the negative sign when the transmitter is on Earth,that means, for the uplink, and, therefore, a positive sign for the downlink. InTable C.1 we can see the values for Vienna’s ground station defocusing loss.

Table C.1: Defocusing Loss for Vienna’s Institute of Communications and Radio-Frequency Engineering ground station.

Elevation Angle degrees 0.1 1 2 3

hs km 0.205B 0.80943 0.76527 0.77655 0.80443b downlink dB -0.91820 -1.16187 -1.09831 -0.94510b uplink dB 0.91820 1.16187 1.09831 0.94510

Therefore, we can say that it will entail losses for the uplink, but will actuallyresult in some gain for the downlink.

Ap.6

Appendix D

Gaseous Absorption using the ITU

Model

In order to calculate the attenuation due to gases in the atmosphere, it has tobe taken into account that there are two different causes of attenuation, dry air,and water vapour, and that each will have a different specific attenuation, γo andγw, respectively, both measured in dB/km [41].

Calculation of the Specific Attenuation due to

Dry Air

The specific attenuation of dry air, γo, for frequencies below 54 GHz, can becalculated using Equation D.1.

γo =

[

7.2 · r2.8t

f 2 + 0.34 · r2p · r1.6t

+0.62 · ξ3

(54− f)1.16·ξ1 + 0.83 · ξ2

]

· f 2 · r2p × 10−3 (D.1)

Where:f is the frequency in GHz,p is the pressure in hPa,rp = p/1013,t is the average temperature of the region in C,rt = 288/ (273 + t), and

ξ1 = ϕ (rp, rt, 0.0717,−1.8132, 0.0156,−1.6515)ξ2 = ϕ (rp, rt, 0.5146,−4.6368,−0.1921,−5.7416)ξ3 = ϕ (rp, rt, 0.3414,−6.5851, 0.2130,−8.5854)ϕ (rp, rt, a, b, c, d) = rp

a · rtb · exp [c · (1− rp) + d · (1− rt)]

Ap.7

Appendices

Calculation of the Specific Attenuation due to

Water Vapour

The specific attenuation of water vapour, γw, can be calculated using Equation D.2.

γw =

(

3.98η1 exp [2.23 (1− rt)]

(f − 22.235)2 + 9.42η12· g (f, 22) + 11.96η1 exp [0.7 (1− rt)]

(f − 183.31)2 + 11.14η12+

+0.081η1 exp [6.44 (1− rt)]

(f − 321.226)2 + 6.29η12+

3.66η1 exp [1.6 (1− rt)]

(f − 325.153)2 + 9.22η12+

+25.37η1 exp [1.09 (1− rt)]

(f − 380)2+

17.4η1 exp [1.46 (1− rt)]

(f − 448)2+

+844.6η1 exp [0.17 (1− rt)]

(f − 557)2· g (f, 557) + 290η1 exp [0.41 (1− rt)]

(f − 752)2· g (f, 752)+

+8.3328× 104η2 exp [0.99 (1− rt)]

(f − 1780)2· g (f, 1780)

)

· f 2 · rt2.5 · ρ× 10−4

(D.2)

Where:

η1 = 0.955 · rp · rt0.68 + 0.006 · ρ (D.3)

η2 = 0.735 · rp · rt0.5 + 0.0353 · rt4 · ρ (D.4)

g(f, fi) = 1 +

(

f − fif + fi

)

(D.5)

ρ is the water vapour density in g/m3.

Calculation of the Equivalent Height for dry air

and water vapour

There is an equivalent height for dry air, ho, and an equivalent height for watervapour, hw. Both are calculated using Equation D.6 and Equation D.10.

ho =6.1

1 + 0.17rp−1.1(1 + t1 + t2 + t3) (D.6)

With:

t1 =4.64

1 + 0.066rp−2.3exp

[

−(

f − 59.7

2.87 + 12.4 exp (−7.9rp)

)2]

(D.7)

Ap.8

Appendices

t2 =0.14 exp (2.12rp)

(f − 118.75)2 + 0.031 exp (2.2rp)(D.8)

t3 =0.0114

1 + 0.14rp−2.6f

−0.0247 + 0.0001f + 1.61× 10−6f 2

1− 0.0169f + 4.1× 10−5f 2 + 3.2× 10−7f 3(D.9)

With the restriction that ho ≤ 10.7rp0.3 for operating frequencies below 70 GHz.

For water vapour, at frequencies below 350 GHz:

hw = 1.66(

1 +1.39σw

(f − 22.235)2 + 2.56σw

+

+3.37σw

(f − 183.31)2 + 4.69σw

+1.58σw

(f − 325.1)2 + 2.89σw

(D.10)

Where:

σw =1.013

1 + exp [−8.6 (rp − 0.57)](D.11)

Calculation of the Gaseous Attenuation

The total attenuation in dB is obtained using Equation D.12

A =Ao + Aw

sin θ(D.12)

Where:

Ao = ho · γo (D.13)

Aw = hw · γw (D.14)

For elevation angles, θ, between 5 and 90.

Calculation of the Gaseous Attenuation of

Vienna’s INTHFT Ground Station

For Vienna’s INTHFT1 ground station calculations, a few parameters were re-quired:

1Institute of Communications and Radio-Frequency Engineering of Vienna University of Tech-nology.

Ap.9

Appendices

The average atmospheric pressure in Vienna for the last year, p, was 1004.1hPa. In order to obtain the average temperature, another recommendation fromthe ITU [42] was consulted. According to Recommendation P.1510 from theITU-R [42], the annual average temperature for Austria is 10 C.

Furthermore, the water vapour density, ρ, can be calculated by means of therelative humidity , obtaining a value of 6.088119 g/m3.

The specific parameters required for the calculation of gas attenuation areshown in Table D.1. Moreover, the results obtained for the gaseous attenuationare presented in Table D.2.

Table D.1: Gaseous attenuation parameters of our ground station at 2.4 GHz.

Parameter Unit Value

Frequency GHz 2.4p hPa 1004.1t C 10ρ g/m3 6.08812γo dB/km 0.00705γw dB/km 8.2828× 10−5

ho km 5.20356hw km 1.66594

Ao dB 0.03668Aw dB 0.00014

Table D.2: Gaseous attenuation of our ground station at 2.4 GHz.

Elevation Angle degrees 5 20 45 90

Agas dB 0.42244 0.10765 0.05207 0.03682

Ap.10

Appendix E

Rain Attenuation using the ITU

Model

Calculation of long-term rain attenuation

statistics from rainfall rate

In order to be able to calculate the rain attenuation, a few parameters are re-quired:

R0.01 in mm/h is the rainfall rate for the location for 0.01% of an averageyear. In Recommendation ITU-R P.837-1 [44] there are maps of the world,divided into zones containing a value for the rainfall rate in each zone.Vienna belongs to Zone K, that, for a percentage of time of 0.01%, gives avalue of 42 mm/h.

hs in km is the height of the ground station above sea level. The antenna ofour ground station will be positioned on the roof of the old Electrical En-gineering building of the University of Technology of Vienna, which is 35 mhigh. Regarding that Vienna is at 170 m above sea level, that makes a totalof 0.205 km.

ϕ in degrees is the latitude of the earth station. For our ground station, thisparameter’s value is 48.22.

Re in km is the effective radius of the Earth. According to the ITU recommen-dation, this value is 8500 km. According to other publications, its value is8470 km [49]. However, because the ITU model is the one being used, thevalue chosen for the calculations is 8500 km.

Detailed below are the steps to follow to calculate the rain attenuation for acertain frequency, for different elevation angles.

STEP 1 Determination of the rain height, hR. In order to do so, in ITU rec-ommendation P.839 [45], it is stated that hR = ho + 0.36 km. ho can beobtained from the maps given in the recommendation, obtaining a value ofho = 3 km. As a result, hR = 3.36 km.

Ap.11

Appendices

STEP 2 Determination of the slant path length, Ls in km, below the rain height.This value depends on the elevation angle, θ. For elevation angles greaterthan 5 , Ls = (hR − hs) / sin θ. On the other hand, for elevation angles, less

than or equal to 5 , Ls = 2·(hR − hs) /

[

√

sin θ2 + 2 (hR − hs) /Re + sin θ

]

STEP 3 Calculation of the horizontal projection, LG, of the slant-path lengthusing LG = Ls · cos θ in km.

STEP 4 Obtaining the specific attenuation, γR, in dB/km using Equation E.1.

γR = k · R0.01α (E.1)

Where:k and α can be calculated by means of the ITU recommendation 838 [46]as follows:

k =[

kH + kV + (kH − kV ) · cos θ2 · cos (2τ)]

/2 (E.2)

α =[

kHαH + kV αV + (kHαH − kV αV ) · cos θ2 · cos (2τ)]

/2k (E.3)

αH , αV , kH , kV are frequency dependent and can be obtained from tables.τ depends on the polarization. It is the polarization inclination angle withthe respect to the horizontal, with a value, for instance, of 45 for circularpolarization.

STEP 5 Calculation of the horizontal reduction factor, r0.01, for 0.01% of thetime.

r0.01 =1

1 + 0.78 ·√

LG·γRf

− 0.38 · (1− exp−2LG)(E.4)

STEP 6 Calculation of the vertical reduction factor, v0.01, for 0.01% of the time.

v0.01 =1

1 +√sin θ

· V (E.5)

V = 31 ·(

1− exp−(θ/(1+κ)))

·√LR · γRf 2

− 0.45 (E.6)

Due to the fact that the latitude of our ground station is greater than 36

κ is equal to 0 degrees.Moreover, LR, depends on another parameter, ξ, measured in degrees.

ξ = arctan

(

hR − hs

LG · r0.01

)

(E.7)

Ap.12

Appendices

LR =

LG·r0.01cos θ

If ξ > 0hR−hs

sin θOtherwise

(E.8)

STEP 7 Calculation of the effective path length, LE in km.

LE = LR · v0.01 (E.9)

STEP 8 The predicted attenuation exceeded for 0.01% of an average year indB, is obatined from Equation E.10.

A0.01 = γR · LE (E.10)

Finally, in Table E.2, are shown the results of this method applied to ourground station at 2.4 GHz and circular polarization. In Table E.1, a list of theparameters used can be seen.

Table E.1: Parameters used to calculate the rain attenuation for our groundstation.

Parameter Value Unit

Frequency 2.4 GHzR0.01 42 mm/hϕ 48.22

hR 3.36 kmhs 0.205 kmRe 8500 kmτ 45

kH 0.0001321kV 0.0001464αH 1.1209αV 1.0085

Table E.2: Rain attenuation of our ground station.

θ 0.1 2 5 20 90

γR dB/km 0.00737 0.00737 0.00737 0.00737 0.00737LE km 580.03703 17.74824 7.00773 1.68841 0.59792

A0.01 dB 4.27406 0.13078 0.05164 0.01244 0.00441

Ap.13

front-end design for a multi-mission, multi-standard satellite … · 2011. 1. 12. · band at...

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