rf antenna ppt

June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 1

RF AntennaRF Antenna(RT-RFA)(RT-RFA)


RT-RFART-RFA

© Copyright 2001 Global Wireless Education Consortium

All rights reserved. This module, comprising presentation slides with notes, exercises, projects and Instructor Guide, may not be duplicated in any way without the express written permission of the Global Wireless Education Consortium. The information contained herein is for the personal use of the reader and may not be incorporated in any commercial training materials or for-profit education programs, books, databases, or any kind of software without the written permission of the Global Wireless Education Consortium. Making copies of this module, or any portion, for any purpose other than your own, is a violation of United States copyright laws.

Trademarked names appear throughout this module. All trademarked names have been used with the permission of their owners.


RT-RFART-RFA

Partial support for this curriculum material was provided by the National Science Foundation's Course, Curriculum, and Laboratory Improvement Program under grant DUE-9972380 and Advanced Technological Education Program under grant DUE‑9950039.

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Table of ContentsTable of Contents

Overview 5

Learning Objectives 6

Antennas as Part of All Communications Systems 7

Fundamental Antenna Characteristics 12

Antenna Radiation Patterns 19

Antenna Types 27

Antenna Configuration Requirements 49

Signal Coverage Problems 56

Advanced System Antennas 63

Antenna Covers and Support Structures 71

Contributors 76


OverviewOverview

How antennas transmit and receive signals

Fundamental characteristics of antennas

Types and features of antennas

Signal coverage problems and how to overcome them

How to perform return loss measurement and antenna gain measurement


Learning ObjectivesLearning Objectives

Explain how an antenna transmits and receives signals Explain fundamental characteristics of antennas

including radiated power, antenna gain, beam width, and front-back ratio

Describe features of different types of antennas Describe the different types of radiation patterns

Explain why and how to measure impedance Explain strategies to address signal coverage problems

Explain antenna diversity and isolation strategies Perform a return loss measurement on an antenna Perform an antenna gain measurement


Antennas as Part of All Antennas as Part of All Communications SystemsCommunications Systems


Antenna System Antenna System ComponentsComponents

Transmit antenna Receive antenna Duplexer Multicoupler Combiner Isolator Tuning cavities Cabling


Antenna OperationAntenna Operation

Antenna - a series of metal wires, rods, or other shapes Transmits when an electric current of radio frequency passes

through it

Current generates electromagnetic field around antenna

Electromagnetic field moves outward from antenna At receiver antenna, does same thing in reverse Tuned to a particular radio wavelength (λ)

Simple fraction or multiple of that length: λ/2, λ/4, etc. Most common length is one-half a wavelength, or λ/2


Antennas, Frequency, and Antennas, Frequency, and WavelengthWavelength

Resonant length changes with frequency and wavelength of electric signal The higher the frequency, the shorter the wavelength, and the

shorter the required antenna The lower the frequency, the longer the wavelength, and the

longer the required antenna

Cellular band antenna Wavelength for cellular telephone transmission is about 0.33 m Length of a cellular antenna should be 0.165 m (λ/2)


Assorted FactsAssorted Facts

Antenna Radiation Pattern Same radiation pattern and gain for transmit and receive antenna

Transceiver Transmitter and receiver electronics housed in a single box Generally use a single antenna for both

Impedance Match Coaxial cable must be terminated with characteristic impedance for

maximum power to be passed to antenna If not, reflections will reduce power passed to antenna and cause

protection circuitry in transmitter to reduce its output power

RF Transmission Planning Optimizes signal strength received by base station and mobile station

regardless of their positions in the network Choice and configuration of antenna system plays an important role


Fundamental Fundamental Antenna Antenna

CharacteristicsCharacteristics


Radiated PowerRadiated Power

Mean power received at any large distance is calculated by the Friis free-space equation:

Pt = transmitted power Pr(d) = received power, a function of transmitter-receiver distance Gt = transmitter antenna gain Gr = receiver antenna gain d = transmitter-receiver separation in meters L = miscellaneous loss factor for loss not related to propagation

L = 1 means no loss L > 1 means loss

λ = wavelength in meters

Ld

GGPdP rtt

r 22

2

)4()(


Antenna BandwidthAntenna Bandwidth

Range of frequencies radiated where lowest and highest frequencies have radiated power that is 3 dB less than the radiated power at frequency with maximum power, f(max) Upper frequency, f(up), is frequency above f(max) where power

is 3 dB lower than f(max) Lower frequency, f(low), is frequency below f(max) where

power is 3 dB lower than f(max)

As a percent, B(p), of center frequency, f(ctr)

%100

ctr

lowupp f

ffB


Antenna GainAntenna Gain

Ratio of antenna’s maximum radiation intensity to maximum radiation intensity from a reference antenna with same input power dBi – If reference antenna is isotropic source of 100% efficiency dBd – If reference antenna is simple dipole of typical efficiency

Gdip (gain with respect to dipole antenna) is 2.15 dB less than Gi (gain with respect to isotropic antenna)

Antenna gain, Gant, is a function of wavelength

Ae = Effective antenna area

2

4

e

antA

G

physicalape AA


Antenna Beam WidthAntenna Beam Width

Antenna achieves gain by concentrating its radiation pattern in a certain direction The greater the gain, the narrower the beam width

Beam width is width of radiated pattern where signal strength is one-half that of maximum signal strength At this point, signal is 3 dB less than that of the maximum Angle between left and right points that are 3 dB down from

maximum is beam angle or beam width

For unidirectional antennas, resulting major lobe of radiation pattern has a certain width Common beam widths for cellular antennas: 60º, 90º, and 120º.


Antenna Front-Back Antenna Front-Back RatioRatio

Measure of antenna’s ability to focus radiated power in intended direction successfully And not interfere with other antennas behind it

Referred to as f-b ratio or f/b ratio Ratio of radiated power in intended direction to radiated

power in opposite direction Ratio of the two gains is the f/b ratio:

180

0

P

P ratio f/b


Frequency Re-UseFrequency Re-Use

7

61

23

4

5

7

61

23

4

5

7

61

23

4

5 Same frequencies used repeatedly in all directions Ability to radiate power in desired direction is critical


Antenna Radiation Antenna Radiation PatternsPatterns


Isotropic Radiation PatternIsotropic Radiation Pattern

Characteristics Completely non-directional antenna Radiates and receives equally well in all directions Theoretical point source or receiver Radiation pattern is spherical

Exists only as a mathematical concept There is no preferential radiation in one direction

Used as a reference to specify gain of a practical antenna


Omnidirectional Radiation Omnidirectional Radiation PatternPattern

Horizontal Pattern Vertical Pattern


Unidirectional Radiation Unidirectional Radiation Pattern Pattern

Horizontal Pattern Vertical Pattern


Radiated Power ComparedRadiated Power Compared

2.15dB

dBi

dBd

Practical antenna

Theoretical halfwave dipole antennaIdeal isotropic radiator

2.15dB

dBi

dBd

Practical antenna

Theoretical halfwave dipole antennaIdeal isotropic radiator


Properties of Properties of Unidirectional Unidirectional AntennasAntennas

Provide increased gain in a limited direction

Multiply use of separate channels by virtue of enabling sectorization

Do not overcome major disadvantages of omnidirectional antennas such as co-channel interference


Antenna PolarizationAntenna Polarization

Polarization is an important property of a radio wave Radio waves have magnetic field H & electrical field E Orientation of electrical field determines polarization

If electrical field is vertical, radio wave is polarized vertically If electrical field is horizontal, radio wave is polarized

horizontally

Antenna of receiver should be oriented in same direction as polarization of transmitter antenna

Mobile antennas should be in the same orientation for best reception This is not always possible with hand-held phones


Voltage Standing Wave Voltage Standing Wave Ratio (VSWR)Ratio (VSWR)

Ratio of maximum voltage to minimum voltage of standing wave along transmission line

Measure of impedance match between antenna and transmission line or coaxial cable The closer VSWR is to one, the greater

the efficiency of electrical power transfer

Formula Pr = Power, reflected

Pi = Power, incident

i

r

i

r

PP

1

PP

1

VSWR


Antenna TypesAntenna Types


Radiation Pattern of Half-Radiation Pattern of Half-wave Dipole Antennawave Dipole Antenna

3-D view Vertical section Horizontal section


Omnidirectional AntennasOmnidirectional Antennas

Omnidirectional antenna Hertz antenna

1


Marconi AntennaMarconi Antenna


Omnidirectional Antenna Omnidirectional Antenna LimitationsLimitations

Radiates and receives equally well in all directions in the horizontal plane Signal power spread uniformly and only small percentage of

radiated power reaches receiver

Receiving antenna receives signals equally well from all directions in horizontal plane For mobile transmitter to be distinguished, it must be stronger

than other signals and the background noise

Limited bandwidth efficiency Very limited re-use of frequencies in adjoining areas


Radiating Coaxial Cable Radiating Coaxial Cable AntennaAntenna

RF in from transmitter RF out (terminated)

Protective sheath

Outer conductorwith holes

Dielectric

Inner conductor

Radiating Coaxial Cable Antenna

Radiating Cable Radiation Pattern


Multi-antenna SystemMulti-antenna SystemExamplesExamples

Pair of directional antennas mounted in different directions Radiation patterns point in opposite directions

Series of antennas around a given building Used when omnidirectional antennas would not be effective

Series of antennas located on the side of a building Minimizes interference with other receivers


Panel AntennasPanel Antennas

Transmitter

Substrate

Radiatingpanel


Unidirectional AntennasUnidirectional Antennas

Referred to as beam antennas Focus beams in one direction Concentrate radiated power into a beam while

minimizing emission in other directions Classifications:

Linear Logarithmic Parasitic

Broadband antenna


Unidirectional AntennasUnidirectional Antennas

Traveling-wave Wire Antenna Folded Dipole Antenna Turnstile Antenna Loop Antenna Rhombic Antenna Yagi-Uda Antenna Log Periodic Antenna Mobile Antenna Sector Antenna


Traveling-wave Wire Traveling-wave Wire AntennaAntenna

Reflectedwave

Dipoleantenna

Incidentwave

Resonant wave of wavelength antenna

Reflectedwave

Incidentwave

Antenna

Traveling wave for non-simple antenna


Folded Dipole AntennaFolded Dipole Antenna

Beam

Driven elementlength =

Reflectorlength2 + 5%

Folded Dipole

Radiation patternFolded dipole antenna


Turnstile AntennaTurnstile Antenna

Turnstile antenna Radiation pattern


Loop AntennaLoop Antenna

Loop antenna Radiation pattern in

horizontal plane


Rhombic AntennaRhombic Antenna

L L

LL

800 Preferred direction of radiation

L L

LL

800


Rhombic Antenna Rhombic Antenna Radiation PatternRadiation Pattern


Yagi-Uda AntennaYagi-Uda Antenna

Yagi-UdaAntenna

Director

Driven element

Reflector


Yagi-Uda AntennaYagi-Uda Antenna

Beam

Directorlength = 2 - 5%

Driven elementlength = /2

Reflectorlength2 + 5%


Log Periodic AntennaLog Periodic Antenna

All elements driven by transmitter

All elements driven but not active at same frequency

Has broad frequency response

Operates on more than one frequency


Mobile Antennas: Collinear Mobile Antennas: Collinear Gain AntennaGain Antenna

Low-gain antenna

Two types

- Through-the-glass

- Standard mount

Have upper and lower portion

separated by phase matching coil


Sector AntennasSector Antennas

120º

60º

60º

3-sector cell 6-sector cell


Sector AntennasSector Antennas

Realistic antenna coverage in 6-sector cell

Antenna overlap in 6-sector cell


Antenna Configuration Antenna Configuration RequirementsRequirements


Antenna Configuration Antenna Configuration RequirementsRequirements

Antenna separation Diversity Isolation Interference Radiation patterns not distorted by obstacles or

reflections


Space DiversitySpace Diversity


Polarization DiversityPolarization Diversity


IsolationIsolation

Needed to avoid distortion due to intermodulation Need to fulfill these isolation values

TX – RX isolation > 30 dB TX – TX isolation > 30 dB

Horizontal physical separation requirements 30 dB isolation: 11.5 λ 800 MHz: 10 feet 1900 MHz: 6 feet

Vertical separation requirement for antenna is 0.2 meter


Antenna DowntiltAntenna Downtilt

Beam of vertically-mounted antenna

Beam of vertically-mounted- antenna with tilted beam


Antenna HeightAntenna Height

Reducing antenna height by 50% will reduce average received signal by 6 dB

Repositioning transmit and/or receive antenna can help maintain system balance


Signal Coverage ProblemsSignal Coverage Problems


Signal Coverage ProblemsSignal Coverage Problems

Design problems Maintenance problems System maturation Site location and geometry Shadows in pattern Nulls in pattern Intermodulation, co-channel, and adjacent channel

interference problems


Resolving Signal Coverage Resolving Signal Coverage ProblemsProblems

Reduce antenna height

Downtilt the antenna

Use higher or lower gain antenna

Use antenna with wider or narrower horizontal or vertical beam width


Return Loss of an AntennaReturn Loss of an Antenna

Power difference between incident and reflected wave in transmission line feeding the antenna

3 dB return loss means reflected power is half of incident power


InterferenceInterference

Multipath condition


InterferenceInterference

time

Sig

na

l Am

plit

ud

e

+

-

Non-fade period

Fading

Rayleigh fading


Co-Channel InterferenceCo-Channel Interference


Advanced System Advanced System AntennasAntennas


Advanced Antenna Advanced Antenna SystemsSystems

Are expensive Increase cell coverage and capacity without building

additional sites Examples

Multi-beam antenna systems Smart antenna systems


Multi-Beam AntennasMulti-Beam Antennas

Standard cell divided into 18 microsectors


Smart Antenna SystemsSmart Antenna Systems

Fixed Beam Strategy Adaptive Beam Strategy


Smart Antenna SystemsSmart Antenna Systems

Time division duplex (TDD) communication systems transmit and receive on same frequency

Frequency division duplex (FDD) transmit and receive on separate frequencies

Capacity for frequency reuse is greater than a standard cell system

Power needed for radio beam is less than for fixed beam strategy

Use code division multiple access method to balance the traffic load


Traffic Load Balancing Traffic Load Balancing Smart Antenna SystemsSmart Antenna Systems

Cell with unbalanced load

Cell with balanced load


Handling Capacity of Handling Capacity of Smart Antenna SystemsSmart Antenna Systems

Adaptive area

Switched beam area

Conventionalsectorization area


Switched Beam versus Switched Beam versus Adaptive Array SystemsAdaptive Array Systems

Factors to consider Interference suppression Range and coverage Spatial division multiple access (SDMA)

Enables wireless system to efficiently use available frequencies where customers are located

Creates a sector for each receiver while maximizing signal strength at receiver and minimizing interference

Uses multiple antennas to combine signals in space at location of receiver


Antenna Covers and Antenna Covers and Support StructuresSupport Structures


Antenna Covers and Antenna Covers and Support StructuresSupport Structures

Antenna covers Protect antenna element from weather Make antenna more aesthetically pleasing

Types of support structures Self-supporting towers Guyed towers Monopole Camouflaged towers Existing structures


Antenna Support Antenna Support StructuresStructures

Self-supporting towers Large 3-D framework of galvanized girders Antenna may be placed at top or any level of tower based on

transmission requirements

Guyed towers Made of crisscrossing steel girders Held in place by guy wires that form a 15 degree vertical angle Antenna may be placed at top or any level of tower based on

transmission requirements



Monopole with 3-sector head

Requires less land area and is more aesthetically pleasing than other structures

• Antenna placement depends on transmission requirements



Camouflaged towers Existing support structure

Buildings Water towers Electric towers Light pole Highway signs

FAA identifies special lighting and/or safety requirement FCC specifies power allowed based on various factors

Terrain Frequencies used Other radio uses in the area


Industry ContributorsIndustry Contributors

AT&T Wireless (http://www.attwireless.com) Ericsson (http://www.ericsson.com) LCC International, Inc. (http://www.lcc.com) Motorola (http://www.motorola.com) Nortel Networks (http://www.nortel.com) Northeast Center for Telecommunications

Technologies(http://nctt.org/index2.htm) RF Globalnet (http://www.rfglobalnet.com)

The following companies provided materials and resource support for this module:


Industry Contributors, Industry Contributors, cont.cont.

Space 2000 (http://www.cdmaonline.com) Telcordia Technologies, Inc (http://www.telcordia.com) Verizon (http://www.verizon.com)

The following companies provided materials and resource support for this module:


Individual ContributorsIndividual ContributorsThe following individuals and their organization or institution provided materials, resources, and development input for this module: Dr. Chaouki Abdallah

University of New Mexico http://www.unm.edu

Dr. Jamil Ahmed British Columbia Institute of Technology http://www.bcit.ca

Dr. John Baldwin South Central Technical College http://[email protected]


Individual Contributors, Individual Contributors, cont.cont.

Dr. Derrek Dunn North Carolina A&T State University http://www.ncat.edu

Mr. Robert Elms ACRE Engineering Services http://[email protected]

Mr. Stuart D. MacPherson Durban Institute of Technology

Dr. James Masi Springfield Technical Community College http://www.stcc.mass.edu/nsindex.asp


Individual Contributors, Individual Contributors, cont.cont.

Ms. Annette Muga Ericsson http://www.ericsson.com

Dr. Dave Voltmer Rose-Hulman Institute of Technology http://www.rose-hulman.edu

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