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7/22/2019 2 Ch 2 Microwave Systems.1
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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
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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
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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.
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Microwave Radio
FMreceiver
FMTransmitter
RFpower
amplifier
BPFBPF
Microwave generator
MixerMixer
Multiplexing and
demultiplexing
equipment
IFIF
From antenna To antenna
Receiver Transmitter
Baseband Repeater
RFRF
To other multiplexersand demultiplexers
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Microwave Radio
FMreceiver
FMTransmitter
RF
poweramplifier
BPFBPF
Microwave generator
MixerMixer
Baseband
amplifier andequalizer
IFIF
From antenna To antenna
Receiver Transmitter
Another Baseband Repeater configuration
RFRF
BasebandBaseband
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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.
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Microwave Radio
RF
poweramplifier
BPFBPF
LocalOscillator
Mixer
LO
From antenna To antenna
Receiver Transmitter
RF Repeater
(RFin LO)RF out
RF in RF out
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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.
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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
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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
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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.
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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
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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.
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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
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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.
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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.
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Microwave Radio
Quad Diversity- Another form of hybrid diversity.
- Undoubtedly provides the most reliabletransmission.
- It is also the most expensive.
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Microwave Radio
Two types of protection switching arrangements:
1. Hot standby2. Diversity
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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.
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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.
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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
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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.
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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
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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.
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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.
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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.
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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
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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
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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
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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.
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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.
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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.
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Microwave Radio
The sky waveis only a source of occasionallong-distance interference and not a reliable signalfor microwave communications purposes.
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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.
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Microwave Radio
Sky wave
Free-space path (line ofsight)
Direct spacewave
Ground reflected wave
Surface wave
Earths surface
Propagation path
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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.
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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.
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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)
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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
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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
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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.
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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.
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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)
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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.
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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
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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
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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.
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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)
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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
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Microwave Radio
Minimum receive carrier power
dBmdBmdBNN
CC 80)104(24min
Minimum transmit carrier power (Pt)
dBmdBmdBCGP St 35.33)80(35.113min
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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.
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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.
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Microwave Radio
Noise factor
)(unitlessrationoisetosignaloutput
rationoisetosignalinputF
Noise figure
FNF
dB
rationoisetosignaloutput
rationoisetosignalinputNF
log10
)(log10
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Microwave Radio
- Noise figureindicates how much the signal-to-noisratio deteriorates as a waveform propagates from theinput to the output of a circuit.
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Microwave Radio
Thermal noise- Most predominant noise.- Generated in all electrical components
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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
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Microwave Radio
TdBT FNF log10)(
In OutA1
F1A2
F2A3
F3An
Fn
Total noise figure
d
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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
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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
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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
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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
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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
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Microwave Radio
k=1
k>1
K
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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
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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
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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
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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
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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
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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
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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
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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
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Microwave Radio
Higher Fresnel Zone Radius
nFFn 1
n= nth Fresnel zone
Microwave Radio
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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
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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
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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
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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
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Microwave Radio
2.Path Parameters
a. Free Space Lossb. Fade Margin
dBmdBmdBm
dBwdBwdB
ITRSLFM
FMITRSLFM
formulasadditonal
)(
)(
:
c. Isotropic Receive Level (IRL)
Microwave Radio
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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
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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
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Microwave Radio
d. FM Improvement Threshold (FMIT)
dBNFMIT dBdB 10_)(_)(
Microwave Radio
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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
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Availability- the percentage of time a system or link meets
performance requirements
MTTRMTBF
MTBFA
MTBF = mean time between failuresMTTR = mean time to repair
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Unavailability- the percentage of time a system or link does
not meet requirements
%100)1( xAU
MTTRMTBF
MTTRU
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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
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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%)
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Microwave RadioGain of Billboard Repeater
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Thank you!