EE 201 ELECTRIC CIRCUITS

King Fahd University of Petroleum & Minerals

Department of Electrical Engineering

EE 418 Introduction to Satellite Communications Major Exam II

Sunday, 30 December 20075:30 pm 7:30 pm

Name:

ID:

Instructor: Dr. Wajih Abu-Al-Saud

ProblemScoreOut of

128

248

324

Total100

Good luck!Important Constants:

Earths average radius (rE) = 6378 km

Speed of light (c)= 2.998 * 108 m/sBoltzmanns constant (k) = 1.38 * 10-23 J/KStandard Noise Temperature T0 = 290 K

Power provided by sun (Psun) = 1.39 kW/m2Problem 1: [28 points]

A LEO satellite at an altitude of 1000 km provides service to a circular region with a radius of 200 km around its sub-satellite point in the Ka band (18 GHz 23 GHz). Assuming a satellite antenna aperture efficiency of 0.75, find the following:a) 3-dB beam width of the antenna that will provide this coverage.

(6 points)b) Radius of the satellite antenna.

(6 points)c) Gain of the satellite antenna.

(6 points)

d) If two identical antennas of this type are placed facing each other at a distance of 10 km apart, and 1 W of power is fed to one of them, what will be the power at the output of the other one (assume no losses other than path loss).

(10 points)

Solutiona)To provide coverage to a circular area of radius 200 km from a height of 1000 km, the beamwidth must be

a)The satellite provides service to a wide range of frequencies (18 GHz 23 GHz), so we have to make sure that its antenna meets specifications for the whole range of frequencies.

So, clearly, to provide the needed coverage, we have to consider the worst case (or smaller radius (since a larger radius will result in a smaller coverage area. The worst case (or smallest radius) results when we consider the smallest wavelength or largest frequency in the band that the satellite operates at.

Radius of satellite =

c)Once the Diameter of the antenna is known, the gain becomes a function of the frequency (or wavelength), so we will have a range of gains between the following values:

c)Assuming the existence of path loss only, the received power will also be a function of frequency and in the following range:

Problem 2: [48 points]

A GEO satellite is part of a communication system that provides full Earth coverage of an FM modulated analog TV channel. The uplink of this system has a C/N ratio of 21.5 dB and C/I ratio of 20 dB. The downlink has a C/I ratio of 22.5 dB. The downlink has the following specifications.

Transmitter Parameters

Trans. Max Output Power 5.0W

Trans. Power Amplifier Backoff 3.5 dB

Trans. AntennaAntenna Aperture Efficiency 0.6

3-dB Beamwidth 17.0(

Edge of Beam Loss 3.0dB

Transmitted Information Signal

Signal Bandwidth 38.0MHz

Carrier Signal Frequency 3.5GHz

Receiver Parameters

Receiver Antenna specificationsAntenna Aperture Efficiency 0.5

Diameter 1.2M

Received Noise (at output of antenna)TIN 35.0K

RF StageNoise Temp. 45.0K

Gain 20.0dB

Mixer StageNoise Temp 100.0K

Gain - 6.0dB

IF StageNoise Temp400.0K

Gain10.0dB

Transmission Path

Max Satellite-Earth Station Distance40 000Km

Clear Air Atmospheric Loss3.0dB

Rain Loss18.0dB

Other Losses2.0dB

a) Find the C/N ratio of the downlink

(24 points)

b) Assuming the signal transmitted towards the satellite in the uplink contains no noise, find the C/N ratio of the signal at the output of the IF stage in the downlink earth station.

(12 points)c) Knowing that the transmitted signal is an FM modulated signal and given that the original TV channel has a bandwidth of 5 MHz, and that pre-emphasis/de-emphasis provides an improvement of 8 dB, find the S/N ratio of the demodulated TV channel. (12 points)

Solutiona)The carrier to noise ratio of the downlink can be obtained by computing the received carrier power and dividing it by the noise power in the signal at the output of the downlink receiver as follows:

Effective transmitted power

The wavelength of operation is

Diameter and Gain of transmitting antenna

Gain of receiving antenna

Path loss is equal to

Clear-air atmospheric loss, Rain loss and other losses are equal to

Now, we are ready to compute the carrier power using the formula:

The system noise temperature is given by

So, the noise power is

So, the downlink carrier to noise ratio

b)The overall carrier to noise ratio is given by (all C/N and C/I must be in linear form)

c)Given the above overall carrier to noise ratio , the signal to noise ratio of the demodulated signal is given by

where

So, the only remaining quantity is which is obtained using the Carsons rule defining the bandwidth of an FM signal as

So,

Therefore,

Problem 3: [24 points]

a) The noise figure (NF) of a satellite receiver system is 2.3 dB. What is the noise temperature of this system?

(6 points)b) The height of a spinner satellite is 4 m and the total area of solar cells on its frame is 35 m2. If these solar cells have an efficiency of 0.2, find the maximum power that these cells can provide when they are exposed to sun light.

(6 points)c) List three (3) quantities that are measured by sensors on a satellite and reported back to base station monitoring the satellite.

(6 points)d) List three (3) subsystems of commercial satellite.

(6 points)Solutiona) Relationship between noise temperature and noise figure of any device is

The noise figure of the system is

So,

b) The circumference of the satellite can be obtained as

So, radius of the spinner satellite is

Therefore, the effective area of a spinner satellite illuminated by sun is

So, maximum power is obtained when sun beams are perpendicular to spinner satellite rotation axis. This maximum power will be:

c) Some of the quantities that are measured by sensors on a satellite and reported back to the base station monitoring the satellite are:i. Pressure of rocket fuel in fuel tanksii. Temperature of different parts of the satellite (including communication components)iii. Power generated by solar cells and consumed by different components of the satelliteiv. Position of different switches turning on/off different components of the satellitev. Satellite Attitude informationvi. Amount of battery charge d) The satellite subsystems that we have studies are

i. Power subsystem

ii. Communication subsystem

iii. Attitude and Orbit Control Systemiv. Telemetry, Tracking, Command, and Monitoring (TTC&M)v. Satellite Antennas

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