2 Ch 2 Microwave Systems.1

7/22/2019 2 Ch 2 Microwave Systems.1

1/88

References:

Kennedy Kennedy and Davis

Tomasi Several Review Materials from:

Blake Excel Review Center

Frenzel PERCDC

Miller CERTI

Roddy and Coolen EDGE / MITRC

Microwave Communications

Ferdinand M. Gabriel

Rose Ellen N. Macabiog


2/88

Microwave RadioIF repeaters

- Also called heterodyne repeaters.- Received RF carrier is down-converted to an IFfrequency, amplified, reshaped, up-converted to anRF frequency, and then retransmitted.

IFamplifier

Equalizer

andshaper

RFpower

amplifier

BPFBPF

Microwave generator

MixerMixer

IF

IFIF

From antenna To antenna

Receiver Transmitter

IF Repeater

RFRF


3/88

Microwave Radio

Baseband repeaters- The received RF carrier is down-converted toan IF frequency, amplified, filtered, and then

further demodulated to baseband.- The baseband signal, which is typicallyfrequency-division-multiplexed voice-band

channels, is further modulated to a mastergroup,supergroup, group, or even channel level.


4/88

Microwave Radio

FMreceiver

FMTransmitter

RFpower

amplifier

BPFBPF

Microwave generator

MixerMixer

Multiplexing and

demultiplexing

equipment

IFIF



Baseband Repeater

RFRF

To other multiplexersand demultiplexers


5/88

Microwave Radio

FMreceiver

FMTransmitter

RF

poweramplifier

BPFBPF

Microwave generator

MixerMixer

Baseband

amplifier andequalizer

IFIF



Another Baseband Repeater configuration

RFRF

BasebandBaseband


6/88

Microwave Radio

RF repeater- The received microwave signal is notdown-converted to IF or baseband.

- The signal is simply mixed (heterodyned)with a local oscillator frequency in a nonlinearmixer.


7/88

Microwave Radio

RF

poweramplifier

BPFBPF

LocalOscillator

Mixer

LO



RF Repeater

(RFin LO)RF out

RF in RF out


8/88

Microwave Radio

Diversity- Microwave systems use line-of-sighttransmission. This means that the transmitting

and receiving antennas must see eye-to-eye.Diversity suggests that:-There is more than one transmission path-There is more than one method of transmission available

between a transmitter and a receiver.Purpose of Diversity:

-The purpose of using diversity is to increase thereliability of the system by increasing its availability.


9/88

Microwave Radio

Frequency Diversity-Modulating two different RF carrier frequencies

with the same IF intelligence, then transmitting both

RF signals to a given destination.

PowerSplitter

BPFA

BPFB

Ch

a

n

n

el

c

o

m

bi

ner

Microwave transmitterfrequency A

Microwave transmitterfrequency B

A

B

IF in

RF out

Frequency Diversity Transmitter


10/88

Microwave Radio

Qualitydetector

BPFA

BPFB

C

h

a

n

n

e

l

s

e

p

a

r

at

or

Microwave

receiver frequency

A

Microwave

receiver frequency

B

A

B

IF out

RF in

Frequency DiversityReceiver

IFswitch


11/88

Microwave Radio

Space Diversity- The output of a transmitter is fed to two ormore antennas that are physically separated by

an appreciable number of wavelengths.- Similarly, at the receiving end, there may bemore than one antenna providing the inputsignal to the receiver.

- If multiple receiving antennas are used, theymust also be separated by an appreciablenumber of wavelengths.


12/88

Microwave Radio

BPF

C

h

a

n

n

e

l

c

o

m

b

in

er

Microwavetransmitter

FMIFin

RF out

Single - channel space diversity

transmitter

RF out


13/88

Microwave Radio

Space-diversity arrangements provide for pathredundancy but not equipment redundancy. Space

diversity is more expensive than frequencydiversity because of the additional antennas andwaveguides. Space diversity, however, providesefficient frequency usage and a substantially

greater protection than frequency diversity.


14/88

Microwave Radio

BPF

C

h

a

n

ne

l

s

e

p

a

r

a

t

or

Microwavereceiver

IF out

RF in

Single - channel space diversityreceiver

RF in


15/88

Microwave Radio

Polarization Diversity- A single RF carrier is propagated with two

different electromagnetic polarizations(vertical and horizontal).- Electromagnetic waves of different

polarizations do not necessarily experiencethe same transmission impairments.


16/88

Microwave Radio

Hybrid Diversity- A somewhat specialized form of diversity,

which consists of a standard frequency-diversitypathwhere the two transmitter/receiver pairs at one end ofthe pathare separated from each other and connected

to different antennas that are vertically separated asin space diversity.


17/88

Microwave Radio

Quad Diversity- Another form of hybrid diversity.

- Undoubtedly provides the most reliabletransmission.

- It is also the most expensive.


18/88

Microwave Radio

Two types of protection switching arrangements:

1. Hot standby2. Diversity


19/88

Microwave Radio

Hot standby protection.- Each working radio channel has a dedicatedbackup or spare channel.- Hot standby systems offer 100% protectionfor each working radio channel.

Diversity protection.- A single backup channel is made available to

as many as 11 working channels.- A diversity system offers 100% protectiononly to the first working channel to fail. If tworadio channels fail at the same time, a service

interruption will occur.


20/88

Microwave Radio

FM Microwave Radio StationsTwo types of FM microwave stations:1. Terminals

2. RepeatersTerminal stations

- Points in the system where baseband signals either originate orterminate.

Repeater stations- Points in a system where baseband signals may be reconfigured.- Points in a system where RF carriers are simply "repeated" oramplified.


21/88

Microwave Radio

Terminal Station- A terminal station consists of four major

sections:

1. The baseband2. Wire line entrance link (WLEL)3. FM-IF4. RF sections


22/88

Microwave Radio

Wireline entrance link (WLEL)

- It serves as the interface between the multiplex- terminal equipment and the FM-IF equipment.- It generally consists of an amplifier and anequalizer (which together compensate for cabletransmission losses) and level-shaping devices

commonly called pre- and deemphasis networks.


23/88


24/88

Microwave Radio

MixerFDMmux

Equalizers Preemphasisnetwork Amp

Deviatorf1

Deviatorf2

IF out to

microwavetransmitter

FDMmux

Equalizers Deemphasisnetwork

Amp FMdiscriminator

Limiter

IF in from

microwavereceiver

(f1 t/2)

(f2 t/2)

(f1- f2) t

(a)

(b)

Baseband Wireline entrancelink

FM-IF section

Microwave terminal station, baseband, WLEL, and FM-IF:

(a) transmitter; (b) receiver


25/88

Microwave Radio

Transmod- A balanced modulator that, when used inconjunction with a microwave generator, power

amplifier, and Bandpass filter, up-converts theIF carrier to an RF carrier and amplifies the RFto the desired output power.


26/88

Microwave Radio

Microwave generator- Provides the RF carrier input to the

up-converter.- It is called a microwave generator rather thanan oscillator because it is difficult to constructa stable circuit that will oscillate in the gigahertzrange.


27/88

Microwave Radio

Isolator- A unidirectional device often made from aferrite material.

- Used in conjunction with a channel-combiningnetwork to prevent the output of one transmitterfrom interfering with the output of anothertransmitter.


28/88

Microwave Radio

Microwave terminal station: (a) transmitter; (b) receiver

IsolatorProtectionswitch

IFamp

Compressionamp

Power ampand BPF

RF out

(a)

IF inTransmod

Microwave

generator

Channel

combiningnetwork

From otherchannels

VF lines toauxiliary channel

To protection

channel

Up-converter

RFIF

(b)

BPFProtection

switchIF amp and

AGC

RF in

IF outReceive

mod

Microwavegenerator

Channel

separationnetwork

To otherchannels

VF lines fromauxiliary channel

From protectionchannel

Down-converter

RFIF


29/88

Microwave Radio

Channel

combiningnetwork

Microwave IF repeater station

BPF

and

poweramp

Channel

separationnetwork

BPF Receivemod

Transmod

6000 MHz

5930 MHz

IF

IF amp/AGCand equalizer

Shiftmod

6180 MHz

70 MHzDown-converter

RF

RF

Isolator

From otherrepeaters

6110 MHz

Microwave

generator5930 MHz

To otherrepeaters

Up-converter

BPF

Shift

oscillator180 MHz


30/88

Microwave Radio

ARx Tx

BRx Tx

CRx Tx

f1 f1 f1 f1

f1

(a)

ARx Tx

BRx Tx

CRx Tx

F2 F1 F2 F1

f1

(b)

(a) Multihop interference and (b) high/low microwave system


31/88

Microwave Radio

Path Characteristicsa.The free-space pathis the line-of-sight path

directly between the transmitting and receiving

antennas (this is also called the direct wave).b. Theground-reflected waveis the portion of the

transmit signal that is reflected off Earth's surface

and captured by the receive antenna.c. The surface waveconsists of the electric andmagnetic fields associated with the currents induced

in Earth's surface.


32/88

Microwave Radio

d. The sum of these three paths (taking into accounttheir amplitude and phase) is called thegroundwave.

e. The sky waveis the portion of the transmit signalthat is returned (reflected) back to Earth's surfaceby the ionized layers of Earth's atmosphere.


33/88

Microwave Radio

For frequencies above about 30 MHz to 50 MHz,the free-spaceand ground-reflected pathsaregenerally the only paths of importance.The surface wavecan also be neglected at thesefrequencies, provided that the antenna heights arenot too low.


34/88

Microwave Radio

The sky waveis only a source of occasionallong-distance interference and not a reliable signalfor microwave communications purposes.


35/88

Microwave Radio

In microwave systems, the surface andsky-wave propagations are neglected, and

attention is focused on those phenomena thataffect the direct and reflected waves.


36/88

Microwave Radio

Sky wave

Free-space path (line ofsight)

Direct spacewave

Ground reflected wave

Surface wave

Earths surface

Propagation path


37/88

Microwave Radio

Fading- A general term applied to the reduction insignal strength at the input to a receiver.

- Applies to propagation variables in thephysical radio path which affect changes in thepath loss between the transmitter at one station

and its normal receiver at the other station.- Can occur under conditions of heavyground fogorwhen extremely cold airmoves over a warm earth.


38/88

Microwave Radio

System Gain- The difference between the nominal outputof a transmitter and the minimum input power

required by a receiver.- must be greater than or equal to the sum ofall the gains and losses incurred by a signal asit propagates from a transmitter to a receiver.

- Represents the net loss of a radio system.


39/88

Microwave Radio

System gain

minCPG tS

Gs= system gain (dB)Pt= transmitter output power (dBm)Cmin = minimum receiver input power for a

given quality objective (dBm)


40/88

Microwave Radio

gainslossesCPt min

Gains: At = transmit antenna gain (dB) relative to an isotropicradiator

Ar = receive antenna gain (dB) relative to an isotropic radiatorLosses: Lp = free-space path loss between antennas (dB)

Lf = waveguide feeder loss (dB) between the distributionnetwork (channeI-combining network or

channel-separation network) and its respective antennaLb = total coupling or branching loss (dB) in the circulators,filters, and distribution network between the output of atransmitter or the input to a receiver and its respective

waveguide feed

Fm= fade margin for a given reliability objective


41/88

Microwave Radio

Microwavepower amp

Pt

C

h

a

nn

el

c

o

m

bi

ner

Lb

From other

microwave

transmitters

C

h

a

nn

el

s

e

p

ar

ator

LbMicrowave

receiverCmin

To other

microwave

receivers

Lf Lf

At ArLp, FM

System gains and losses


42/88

Microwave Radio

rtbfpmtS AALLLFCPG min

where all values are expressed in dB or dBm.

Because system gain is indicative of a net loss, thelosses are represented with positive dB values andthe gains are represented with negative dB values.


43/88

Microwave Radio

Free-Space Path Loss- Sometimes called spreading loss.- the loss incurred by an electromagnetic wave

as it propagates in a straight line through avacuum with no absorption or reflection ofenergy from nearby objects.- Frequency dependent and increases withdistance.


44/88

Microwave Radio

Free-space path loss

22

44

c

fDDLP

Lp = free space path loss (unitless)D = distance (meters)

f = frequency (hertz) = wavelength (meters)c= velocity of light in free space (3x108 m/s)


45/88

Microwave Radio

Fade Margin- This is the fudge factor included in the

system gain equation that considers thenon-ideal and less predictable characteristics ofradio wave propagation such as multi pathpropagation (multipath loss)and terrainsensitivity.


46/88

Microwave RadioNon diversity system

70)1log(10)6log(10log30 RABfDFm

30logD = multipath effect10log(6ABf) = terrain sensitivity

10log(1-R) = reliability objectivesFm = fade margin (dB)D = distance (kilometers)f = frequency (gigahertz)R = reliability expressed as decimal

1

R = reliability objective for a one-way 40-km routeA = roughness factor:

= 4 over a very smooth terrain= 1 over an average terrain

= 0.25 over a very rough, mountainous terrain


47/88

Microwave Radio

B = factor to convert the worst-month probability to anannual probability= 1 to convert an annual availability to a

worst-month basis= 0.5 for humid areas= 0.25 for average inland areas= 0.125 for very dry or mountainous areas


48/88

Microwave Radio

Receiver Threshold- The minimum wideband carrier power(Cmin) at the input to a receiver that will

provide a usable baseband output.- Sometimes called the receiver sensitivity

Carrier-to-noise (C/N) ratio

- Probably the most important parameterconsidered when evaluating the performanceof a microwave communications system.


49/88

Microwave Radio

Input noise power

KTBNN = noise power (watts)

K = Boltzmann's constant (1.38 X 10-23J/K)T = equivalent noise temperature of the receive (kelvin) (room temperature = 290 kelvin)

B = noise bandwidth (hertz)


50/88

Microwave Radio

BKTKTB

N dBm log10001.0

log10001.0

log10)(

For a 1-KHz bandwidth at room temperature

BN

dBmx

N

dBm log10174

174001.0

290)1038.1(log10

)(

23


51/88

Microwave Radio

Minimum receive carrier power

dBmdBmdBNN

CC 80)104(24min

Minimum transmit carrier power (Pt)

dBmdBmdBCGP St 35.33)80(35.113min


52/88

Microwave Radio

Carrier-to-Noise Versus Signal-to-Noise Ratio

Carrier-to-noise ratio (C/N)- The ratio of the wideband "carrier"

to the wideband noise power (the bandwidthof the receiver).

Signal-to-noise ratio (S/N)

- Apostdetection(after the FM demodulator)ratio.


53/88

Microwave Radio

Noise Factor and Noise Figure

Noise factor (F)and Noise figure (NF)

- These are figures of merit used to indicatehow much the signal-to-noise ratio deterioratesas a signal passes through a circuit or series ofcircuits.

Noise factor- a ratio of input signal-to-noise ratio to

output signal-to-noise ratio.


54/88

Microwave Radio

Noise factor

)(unitlessrationoisetosignaloutput

rationoisetosignalinputF

Noise figure

FNF

dB

rationoisetosignaloutput

rationoisetosignalinputNF

log10

)(log10


55/88

Microwave Radio

- Noise figureindicates how much the signal-to-noisratio deteriorates as a waveform propagates from theinput to the output of a circuit.


56/88

Microwave Radio

Thermal noise- Most predominant noise.- Generated in all electrical components


57/88

Microwave Radio

Total noise factor of several cascaded amplifiers

32121

3

1

21

111

AAA

F

AA

F

A

FFF nT

FT = total noise factor for n cascaded amplifiersF1 = noise factor, amplifier 1F2 = noise factor, amplifier 2F3 = noise factor, amplifier 3

Fn = noise factor, amplifier nA1 = power gain, amplifier 1A2 = power gain, amplifier 2A3 = power gain, amplifier 3


58/88

Microwave Radio

TdBT FNF log10)(

In OutA1

F1A2

F2A3

F3An

Fn

Total noise figure

d


59/88

Microwave Radio

BKTN ed

Te = equivalent noise temperature.No = total output noise power of an amplifier (watts)Ni = total input noise power of an amplifier (watts)A = power gain of an amplifier (unitless)

Mi R di


60/88

Microwave Radio

)( eoeo

dio

TTAKBNBAKTAKTBN

andANANN

TT

T

TT

AKTB

TTAKB

AN

N

NSA

NS

NS

NS

F

eee

i

o

out

i

out

in

T

1

)(

Signal

in

Signal

outNO

Ni

T

NdTeA

Noise figure as a function oftemperature

Mi R di


61/88

Microwave Radio

Microwave Engineering Procedures:1. Selection of sites that are line-of-sight to each

other (includes tower location).

2. Selection of an operating frequency band.3. Selection of radio equipment, transmission mediaand tower.

4. Development of path profiles to determine towerheights.

5. Link budget calculations.

6. Making path surveys.

Mi R di


62/88

Microwave Radio

9. Installation.10. Testing of the link (includes equipment lineup,

beam alignment, equipment inspection).11. Acceptance by the customer.

7. Establishment of a frequency plan and necessaryoperational parameters.

8. Equipment configuration to achieve the most

economical fade margin set in step 5.

Mi R di


63/88

Microwave Radio

The K-factor:- This is a numerical figure that considers thenon-ideal condition of the atmosphere resultingto atmospheric refraction that causes the raybeam to be bent toward the earth or away fromthe earth.

o

e

rr

radiusearthTrueradiusearthEffectivek

Mi R di


64/88

Microwave Radio

k=1

k>1

K


65/88

Microwave Radio

Effective Earth Radius (re)

)005577.0()(04665.01 S

N

o

kmee

rr

NS = Surface refractivityro = true earth radius (6370km)

)( 1057.0 Sh

OS eNN

hS = height of potential site in km

Mi R di


66/88

Microwave Radio

K-curve conditions:a.Sub-standard condition

1k - the microwave beam is bent away from theearth. It is as if the earths curvature is extended orthe earth bulge is effectively increased hence, the patis shortened and the tower must be increased.

Mi R di


67/88

Microwave Radio

b. Standard condition

3

4k

Under this condition, the fictitious earthradius appears to be longer than the true earths

radius, thus, the earth path is assumed to be smooth

(no obstacles besides mid-path earth bulge) such thatthe microwave beam is neither bent toward the earthor away from the earth.

Mi R di


68/88

Microwave Radio

c. Super-standard condition

3

4k

This condition results in an effectiveflattening of the equivalent earths curvatureandthe microwave beam is bent toward the earth, whichallows decreasing the tower heights.

Mi R di


69/88

Microwave Radio

d. Infinity condition (Flat earth condition)

k

This condition results to zero curvature (as ifthe earth is very flat) and the microwave beamfollows the earths curvature.

Mi R di


70/88

Microwave Radio

Earth Bulge (eb)- This is the height at which an obstacle along

the path is further raised due to the earths curvature.

75.12

5.1

)(2)(1

)(

)(2)(1

)(

KmKm

mb

mimi

ftb

dde

dde

Mi R di


71/88

Microwave Radio

Fresnel Clearance- Another factor that must be added to theobstacle height to obtain an overall effective obstacleheight.

- It derives from EM wave theory that awavefront has expanding properties as it travelsthrough space.

Fresnel Zone Radius- The amount of additional clearance that mustbe allowed to avoid problems with the Fresnelphenomenon.

Mi r R di


72/88

Microwave Radio

)()(

)(2)(1

)(1

)()(

)(2)(1

)(1

3.17

1.72

kmGHz

kmkm

m

miGHz

mimi

ft

Df

dd

F

Df

ddF

60% of the 1st Fresnel Zone Radius (0.6F1)- This is a situation when there is no net change in

attenuation or no gain, no loss condition occurs andwhen 60% of the first Fresnel radius clears a path obstructionin microwave systems.

Micro a e Radio


73/88

Microwave Radio

Higher Fresnel Zone Radius

nFFn 1

n= nth Fresnel zone

Microwave Radio


74/88

Microwave Radio

Microwave Link Budget CalculationsPath Profile

- This is a graphical presentation of the path

traveled by the radio waves between the two ends ofthe link.

- It determines the location and height of the

antenna at each end of the link.- It ensures that the link is free of

obstructions, such as hills, trees, buildings, etc.

Microwave Radio


75/88

Microwave Radio

1. Transmit Parametersa. Transmit Power (dBw, dBm)b. Transmitter Transmission Line Loss (dB

c. Transmitter Antenna Gain (dB)

ftGHZdBT

mGHzdBT

T

DfG

DfG

DDG

log20log205.7

log20log208.17

6

)(

)(

22

Microwave Radio


76/88

Microwave Radio

d. Effective Isotropically Radiated Power (EIRP)- The actual power going into the antennamultiplied by its gain with respect to an isotropicradiator.

)()()( dBTdBwTdBw

tt

GPEIRP

GPEIRP

)()()()( dBTdBTdBwTdBw

T

TT

LGPEIRPLGPEIRP

Microwave Radio


77/88

Microwave Radio

Effective Radiated Power (ERP)- The power input multiplied by the antenna

gain measured with respect to a half-wave dipole.

- An ideal half-wave dipole has a gain of 2.14 dBi.

Therefore, EIRP is 2.14 dB greater than the ERP for thesame antenna-transmitter combination.

dBERPEIRP 14.2

Microwave Radio


78/88

Microwave Radio

2.Path Parameters

a. Free Space Lossb. Fade Margin

dBmdBmdBm

dBwdBwdB

ITRSLFM

FMITRSLFM

formulasadditonal

)(

)(

:

c. Isotropic Receive Level (IRL)

Microwave Radio


79/88

Microwave Radio

3. Receive Parametersa. Receiver Antenna Gain (dB)b. Receiver Transmission Line Loss (dB)c. Carrier-to-Noise Ratio (C/N)

dBdBm

dB

NRSLN

C

)(

d. Receiver Sensitivity

Microwave Radio


80/88

Microwave Radio

4. Miscellaneous Parametersa. Net Path Loss (NPL)b. Receive Signal Level (RSL)c. Noise Threshold

dBdBm

dBdBm

dBdBw

dBdBw

NFBNor

NFmW

kTBN

NFBNor

NFkTBN

log10174

1log10

log10204

log10

)(

)(

)(

)(

Microwave Radio


81/88

Microwave Radio

d. FM Improvement Threshold (FMIT)

dBNFMIT dBdB 10_)(_)(

Microwave Radio


82/88

Microwave Radio

Reliability

%100)1( xoutageR

For multi-hop link

nS xRxRxRRR ...321

Outage = the amount of time that therequirements will not be met

R1, R2, Rn= individual reliability

Microwave Radio


83/88

Microwave Radio

Availability- the percentage of time a system or link meets

performance requirements

MTTRMTBF

MTBFA

MTBF = mean time between failuresMTTR = mean time to repair

Microwave Radio


84/88

Microwave Radio

Unavailability- the percentage of time a system or link does

not meet requirements

%100)1( xAU

MTTRMTBF

MTTRU

Microwave Radio


85/88

Microwave Radio

Passive Repeatersa.Back-to-back Parabolic Antenna Repeater or

Back-to-back HornAntenna Repeater

- consists of two parabolic antennasor horn antennas connected back-to-backthrough a short piece of waveguide

- this is relatively inefficient, seldomused except in extremely short paths

Microwave Radio


86/88

Microwave Radio

b. Billboard Repeater

-flat, metal-type reflector, which acts as a microwavemirror that reflects EM waves surfaces of adequate

flatness is highly efficient (close to 100%)

Microwave Radio


87/88

Microwave RadioGain of Billboard Repeater


88/88

Thank you!

Documents

2 Ch 2 Microwave Systems.1