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Chapter 14 Introduction to Microwave Systems

14.1 System aspects of antennas

radiation pattern, directivity, efficiency, gain, temperature

14.2 Microwave communication systems

Friis formula, transmitter and receiver, receiver noise

characteristics

14.3 Radar systems

radar equation

14.4 Radiometry

radiometer

14.5 Microwave propagation

atmospheric effects

14.6 Other applications and topics

microwave oven, energy transfer

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14.1 System aspects of antennas

• antenna characteristics

radiation pattern

directivity

efficiency

gain

equivalent noise temperature

2 * 2( , ) ( , ) ( , ) ( , )F r E H r S

max max

2

4 4 4

( , )sin

e

rad

F F AD

P F d d

in

rad

P

P

DG

(1 )A b pT T T

S

PA l

e

Discussion

1. Ex.14.3 Calculate TA with η=1 and an antenna directivity

D(dB)

-90 -30 0 30 90

10

30

2

1 30 90

0 1 30

1 90

0 1

10 , 30 noise temperature

100 ,30 90

10 1000sin 10 10sin 100 10sin= 86.4

1000sin 10sin

B

A b

Kbackground T

K

d d d sidelobeT T K

regiond d

( , ) ( , )sin

( , )sin

B

b

B

T D d dT

T d d

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14.2 Microwave communication systems

• Friis power transmission formula

Pt R Pr

Gt Gr2

2 24 (4 )

t t e t t rr

PG A PG GP

R R

Discussion

1. Ex.14.4 a DBS satellite @12.45GHz, Pt =120W, Gt =34dB 2m dia.

=1.7º, slant range 39000km, ground receiving terminal Gr =33.5dB

18in dia. =6º, TA=50K, NF=0.7dB, BW=20MHz

2

2

(1)transmitter 120 2512 54.8

(2) ( 1) 50 (1.179 1) 290 100.8

2239receiver 13.5 /

100.8

(3) 117.9 87.9(4 )

(4) 17.7 >

t t

e A LNB A o

t t rr

r LNB

e LNB

EIRP P G dBm

receiver T T T T F T K

GdB K

T

P G GP dBW dBm

R

P GCNR dB syst

kT BG

argem link m in

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• noise analysis of a microwave receiver

GA, , Tp LT, Tp GRF, TRF LM, TM GIF, TIF

Tb Ni, Si No, So

equivalent noise temperature

(1) antenna

(2) cable(1 ) ,A b p i AT T T N kT B

( 1)TL T pT L T

TREC

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o/p signal power

o/p noise power

sysi

MT

IFRFio GS

LL

GGSS

RECTTLRECTL

RF

MIF

RF

MRFREC TLTT

G

LT

G

TTT

(3) receiver

( )

( )

[ (1 ) ( 1) ]

o i TL REC sys

A TL REC sys

b p T p T REC sys

sys sys

o io

o sys

N N kBT G

kB T T G

kB T T L T L T G

kBT G

S SSNR

N kBT

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Discussion

1. Ex14.5 a 4 GHz receiver with BW=1MHz, Si = -80dBm

1.5 1.41 ( 1) 123 ,

6 4, 7 ( 1) 1163 ,

3 ( 1) 289

1.1 ( 1) 84

20 100, 30 1000

304

7

T TL T o

M M M M o

RF RF RF o

IF IF IF o

RF IF

M IF MREC RF

RF RF

sys A TL T REC

L dB T L T k

L dB F dB T F T k

F dB T F T k

F dB T F T k

G dB G dB

T T LT T k

G G

T T T L T

62 = 110

80 110 30

sys

io

sys

k kBT dBm

SSNR dB

kBT

0.9, 200 , 300 210

115 35

b p A

i A i

T k T k T k

N kT B dBm SNR dB

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• noise analysis of a digital communication receiver

Ex14.6 a LEO communication satellite f=16GHz,,Pt=80W, Gt=20dB,

R=940km, a QPSK receiving handset Gr=1dB, Tsys=750K, Latm=2dB

BER=0.01, find Rb,min for 10dB link margin

bit energy: ( )

noise power desity

1, : signal power, : bit period, :bit rate

bb

o

b bb b

o o o b b bb

EP BER

n

E ST S S SBS T R

Nn n n R NR RR

B

2

2

15min

min

,max

15min min min

,max23

49 20 1 176 2 108(4 )

108 10 118 1.58 10

QPSK 0.01 5 3.16

1 1.58 1048

3.16 1.38 10 750

t t rr

b

o b

o o ob

b b sys b sys

P G GP dBm

R

S dBm W

E S BBER dB

n NR

n S B n S B n SR kbps

E N E kT B E kT

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14.3 Radar systems

• radar (radio detection and ranging) equation

4

min

3

22

max43

22

22 )4()4(4

1

4 P

GPR

R

GPA

RR

GPP tt

et

r

Discussion

1. Ex14.7 radar @10GHz, Pt=2kW, G=28dB, =12m2 , Pmin=-90dBm

Rmax = 8114km

2. pulse radar detect target range and direction

3. Doppler radar detect target radial velocity

4. radar cross section (p.696, Table 14.3)

e.g. bird 0.01m2, missile 0.5m2, person 1m2, fighter 3-8m2,

airplane 100m2, truck 200m2

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5. SIR-C (1994) microwave image of Taipei area

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14.4 Radiometry

• radiometer

TP=kTBB=keTB

T: physical temperature

TB: brightness temperature

e: emmisivity

0 e 1

Discussion

1. radiometer measures the object noise powerTBobject

physical parameters (p.699)

e.g. soil moisture, ocean surface wind speed, target image,

mapping of galactic objects,…….

2. usually TB<TR receiver temperature, Vo=Gk(TB+TR )B,

TR can be derived from the Y-factor calibration

3. measurement errors due to

noise fluctuation increase integration time

receiver gain fluctuation Dicke radiometer

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4. SMA (sub-millimeter array) (1983, 1996~) 200GHz-900GHz

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5. AMiBA (Array for Microwave Background Anisotrophy)宇宙背景輻射陣列望遠鏡(2001~) 85GHz-105GHz

To Correlators

From LO

Source

From Calibrated

Noise Source

Component Chain

Vacuum Window

Corrugated

Feed

Noise Coupler

Transition

OMT

Isolator

RF

Pre-Amplifier

Isolator

RF Post-

Amplifier

Sub-Harmonic

Mixer

IF Amplifiers

Cryogenic

Environment

High-Pass

Filter

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14.5 Microwave propagation

Discussion

1. “line of sight propagation”, 1/R2, for microwaves

satellite communication

2. atmospheric attenuation effects (p.703, Fig.14.29)

negligible for f<10GHz

water vapor resonance @ 22.2GHz, 183.3GHz

O2 resonance @ 60GHz, 120GHz

“microwave window” @ 35GHz, 94GHz, 135GHz

earth remote sensing

3. ground reflections

fading or scintillation problems for wireless communication

in urban area

clutter problem for radar

4. plasma frequency 8MHz, total reflection from ionsphere

for f<fp short wave radio

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14.6 Other applications and topics

Discussion

1. microwave oven @ 2.45GHz

conduction loss for large tan of material

2. energy tansfer nonpilot airplane, solar power satellite station,

mobile phone, …

3. micrwave exposure thermal effects, IEEE Standard C95.1-2005

power density: 10W/m2~1mW/cm2

0.1 1 10 100 f (GHz)

100

10

1

W/m2

6 min. exposure

30 min. exposure

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4. Ex 14.8 a 18GHz microwave antenna 36dB gain and 10W radiation

power density at 20 m away

2

2

2 2 2

8 @ 10 400010

4 4 20 0.8 @ 10

in W m main lobeP GS W m

R W m dB sidelobe

ADS examples: Ch14_prj