Transcript

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
Microwave Radio

IF repeaters
- Also called heterodyne repeaters.
- Received RF carrier is down-converted to an IF
frequency, amplified, reshaped, up-converted to an
RF frequency, and then retransmitted.
IF
amplifier
Equalizer
and
shaper
RF
power
amplifier
BPF BPF
Microwave generator
Mixer Mixer
IF
IF
IF
From antenna To antenna
Receiver Transmitter
IF Repeater
RF RF
Microwave Radio

Baseband repeaters
- The received RF carrier is down-converted to
an IF frequency, amplified, filtered, and then
further demodulated to baseband.
- The baseband signal, which is typically
frequency-division-multiplexed voice-band
channels, is further modulated to a mastergroup,
supergroup, group, or even channel level.
Microwave Radio

FM
receiver
FM
Transmitter
RF
power
amplifier
BPF BPF
Microwave generator
Mixer Mixer
Multiplexing and
demultiplexing
equipment
IF
IF
From antenna To antenna
Receiver Transmitter
Baseband Repeater
RF RF
To other multiplexers
and demultiplexers
Microwave Radio

FM
receiver
FM
Transmitter
RF
power
amplifier
BPF BPF
Microwave generator
Mixer Mixer
Baseband
amplifier and
equalizer
IF
IF
From antenna
To antenna
Receiver Transmitter
Another Baseband Repeater configuration
RF RF
Baseband Baseband
Microwave Radio
RF repeater
- The received microwave signal is not
down-converted to IF or baseband.
- The signal is simply mixed (heterodyned)
with a local oscillator frequency in a nonlinear
mixer.
Microwave Radio
RF
power
amplifier
BPF BPF
Local
Oscillator
Mixer
LO
From antenna
To antenna
Receiver Transmitter
RF Repeater
(RFin ± LO)
RF out
RF in RF out
Microwave Radio
Diversity
- Microwave systems use line-of-sight
transmission. 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 the
reliability of the system by increasing its availability.
Microwave Radio

Frequency Diversity
-Modulating two different RF carrier frequencies
with the same IF intelligence, then transmitting both
RF signals to a given destination.
Power
Splitter
BPF
A
BPF
B
C
h
a
n
n
el

c
o
m
bi
n
er
Microwave transmitter
frequency A
Microwave transmitter
frequency B
A
B
IF in
RF out
Frequency Diversity Transmitter
Microwave Radio
Quality
detector
BPF
A
BPF
B
C
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s
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p
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a
t
o
r
Microwave
receiver frequency
A
Microwave
receiver frequency
B
A
B
IF out
RF in
Frequency Diversity
Receiver
IF
switch
Microwave Radio
Space Diversity
- The output of a transmitter is fed to two or
more antennas that are physically separated by
an appreciable number of wavelengths.
- Similarly, at the receiving end, there may be
more than one antenna providing the input
signal to the receiver.
- If multiple receiving antennas are used, they
must also be separated by an appreciable
number of wavelengths.

Microwave Radio

BPF
C
h
a
n
n
e
l

c
o
m
b
i
n
e
r
Microwave
transmitter
FM – IF
in
RF out
Single - channel space diversity
transmitter
RF out
Microwave Radio
Space-diversity arrangements provide for path
redundancy but not equipment redundancy. Space
diversity is more expensive than frequency
diversity because of the additional antennas and
waveguides. Space diversity, however, provides
efficient frequency usage and a substantially
greater protection than frequency diversity.
Microwave Radio

BPF
C
h
a
n
n
e
l

s
e
p
a
r
a
t
o
r
Microwave
receiver
IF out
RF in
Single - channel space diversity
receiver
RF in
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 experience
the same transmission impairments.
Microwave Radio
Hybrid Diversity
- A somewhat specialized form of diversity,
which consists of a standard frequency-diversity
path where the two transmitter/receiver pairs at one end of
the path are separated from each other and connected
to different antennas that are vertically separated as
in space diversity.
Microwave Radio
Quad Diversity
- Another form of hybrid diversity.
- Undoubtedly provides the most reliable
transmission.
- It is also the most expensive.
Microwave Radio
Two types of protection switching arrangements:

1. Hot standby
2. Diversity
Microwave Radio
Hot standby protection.
- Each working radio channel has a dedicated
backup or spare channel.
- Hot standby systems offer 100% protection
for 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% protection
only to the first working channel to fail. If two
radio channels fail at the same time, a service
interruption will occur.
Microwave Radio
FM Microwave Radio Stations
Two types of FM microwave stations:
1. Terminals
2. Repeaters
Terminal stations
- Points in the system where baseband signals either originate or
terminate.
Repeater stations
- Points in a system where baseband signals may be reconfigured.
- Points in a system where RF carriers are simply "repeated" or
amplified.
Microwave Radio
Terminal Station
- A terminal station consists of four major
sections:

1. The baseband
2. Wire line entrance link (WLEL)
3. FM-IF
4. RF sections
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 an
equalizer (which together compensate for cable
transmission losses) and level-shaping devices
commonly called pre- and deemphasis networks.
Microwave Radio
IF section
- The FM terminal equipment generates a
frequency-modulated IF carrier.
RF section.
- The IF signal enters the transmitter through a
protection switch.
- The IF and compression amplifiers help keep
the IF signal power constant and at
approximately the required input level to the
transmit modulator (transmod).
Microwave Radio
Mixer
FDM
mux
Equalizers
Preemphasis
network Amp
Deviator
f1
Deviator
f2
IF out to
microwave
transmitter
FDM
mux
Equalizers Deemphasis
network
Amp
FM
discriminator
Limiter
IF in from
microwave
receiver
(f1 ± At/2)
(f2 ± At/2)
(f1- f2) ± At
(a)
(b)
Baseband Wireline entrance
link
FM-IF section
Microwave terminal station, baseband, WLEL, and FM-IF:
(a) transmitter; (b) receiver
Microwave Radio
Transmod
- A balanced modulator that, when used in
conjunction with a microwave generator, power
amplifier, and Bandpass filter, up-converts the
IF carrier to an RF carrier and amplifies the RF
to the desired output power.
Microwave Radio
Microwave generator
- Provides the RF carrier input to the
up-converter.
- It is called a microwave generator rather than
an oscillator because it is difficult to construct
a stable circuit that will oscillate in the gigahertz
range.
Microwave Radio
Isolator
- A unidirectional device often made from a
ferrite material.
- Used in conjunction with a channel-combining
network to prevent the output of one transmitter
from interfering with the output of another
transmitter.
Microwave Radio
Microwave terminal station: (a) transmitter; (b) receiver
Isolator
Protection
switch
IF
amp
Compression
amp
Power amp
and BPF
RF out
(a)
IF in
Transmod
Microwave
generator
Channel
combining
network
From other
channels
VF lines to
auxiliary channel
To protection
channel
Up-converter
RF IF
(b)
BPF
Protection
switch
IF amp and
AGC
RF in
IF out
Receive
mod
Microwave
generator
Channel
separation
network
To other
channels
VF lines from
auxiliary channel
From protection
channel
Down-converter
RF IF
Microwave Radio
Channel
combining
network
Microwave IF repeater station
BPF
and
power
amp
Channel
separation
network
BPF
Receive
mod
Transmod
6000 MHz
5930 MHz
IF
IF amp/AGC
and equalizer
Shift
mod
6180 MHz
70 MHz
Down-converter
RF
RF
Isolator
From other
repeaters
6110 MHz
Microwave
generator
5930 MHz
To other
repeaters
Up-converter
BPF
Shift
oscillator
180 MHz
Microwave Radio
A
Rx Tx
B
Rx Tx
C
Rx Tx
f1
f1 f1 f1
f1
(a)
A
Rx Tx
B
Rx Tx
C
Rx Tx
F2
F1 F2 F1
f1
(b)
(a) Multihop interference and (b) high/low microwave system
Microwave Radio
Path Characteristics
a.The free-space path is the line-of-sight path
directly between the transmitting and receiving
antennas (this is also called the direct wave).
b. The ground-reflected wave is the portion of the
transmit signal that is reflected off Earth's surface
and captured by the receive antenna.
c. The surface wave consists of the electric and
magnetic fields associated with the currents induced
in Earth's surface.
Microwave Radio
d. The sum of these three paths (taking into account
their amplitude and phase) is called the ground
wave.
e. The sky wave is the portion of the transmit signal
that is returned (reflected) back to Earth's surface
by the ionized layers of Earth's atmosphere.
Microwave Radio
For frequencies above about 30 MHz to 50 MHz,
the free-space and ground-reflected paths are
generally the only paths of importance.
The surface wave can also be neglected at these
frequencies, provided that the antenna heights are
not too low.
Microwave Radio
The sky wave is only a source of occasional
long-distance interference and not a reliable signal
for microwave communications purposes.
Microwave Radio
In microwave systems, the surface and
sky-wave propagations are neglected, and
attention is focused on those phenomena that
affect the direct and reflected waves.
Microwave Radio
Sky wave
Free-space path (line of
sight)
Direct space
wave
Ground reflected wave
Surface wave
Earth’s surface
Propagation path
Microwave Radio
Fading
- A general term applied to the reduction in
signal strength at the input to a receiver.
- Applies to propagation variables in the
physical radio path which affect changes in the
path loss between the transmitter at one station
and its normal receiver at the other station.
- Can occur under conditions of heavy
ground fog or when extremely cold air
moves over a warm earth.
Microwave Radio
System Gain
- The difference between the nominal output
of a transmitter and the minimum input power
required by a receiver.
- must be greater than or equal to the sum of
all the gains and losses incurred by a signal as
it propagates from a transmitter to a receiver.
- Represents the net loss of a radio system.
Microwave Radio
System gain
min
C P G
t S
÷ =
Gs = system gain (dB)
Pt = transmitter output power (dBm)
Cmin = minimum receiver input power for a
given quality objective (dBm)
Microwave Radio
gains losses C P
t
÷ > ÷
min
Gains: At = transmit antenna gain (dB) relative to an isotropic
radiator
Ar = receive antenna gain (dB) relative to an isotropic radiator
Losses: Lp = free-space path loss between antennas (dB)
Lf = waveguide feeder loss (dB) between the distribution
network (channeI-combining network or
channel-separation network) and its respective antenna
Lb = total coupling or branching loss (dB) in the circulators,
filters, and distribution network between the output of a
transmitter or the input to a receiver and its respective
waveguide feed
Fm = fade margin for a given reliability objective
Microwave Radio
Microwave
power amp
P
t


C
h
a
n
n
el

c
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m
bi
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e
r
L
b

From other
microwave
transmitters


C
h
a
n
n
el

s
e
p
ar
at
or
L
b

Microwave
receiver
C
min

To other
microwave
receivers
Lf Lf
A
t
A
r

Lp, FM
System gains and losses
Microwave Radio
r t b f p m t S
A A L L L F C P G ÷ ÷ + + + > ÷ =
min
• where all values are expressed in dB or dBm.
Because system gain is indicative of a net loss, the
losses are represented with positive dB values and
the gains are represented with negative dB values.
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 a
vacuum with no absorption or reflection of
energy from nearby objects.
- Frequency dependent and increases with
distance.
Microwave Radio
Free-space path loss
2 2
4 4
|
.
|

\
|
=
|
.
|

\
|
=
c
fD D
L
P
t
ì
t
Lp = free space path loss (unitless)
D = distance (meters)
f = frequency (hertz)
ì = wavelength (meters)
c = velocity of light in free space (3x108 m/s)

Microwave Radio
Fade Margin
- This is the “fudge factor” included in the
system gain equation that considers the
non-ideal and less predictable characteristics of
radio wave propagation such as multi path
propagation (multipath loss) and terrain
sensitivity.
Microwave Radio
Non diversity system
70 ) 1 log( 10 ) 6 log( 10 log 30 ÷ ÷ ÷ + = R ABf D Fm
30logD = multipath effect
10log(6ABf) = terrain sensitivity
10log(1-R) = reliability objectives
Fm = fade margin (dB)
D = distance (kilometers)
f = frequency (gigahertz)
R = reliability expressed as decimal
1 – R = reliability objective for a one-way 40-km route
A = roughness factor:
= 4 over a very smooth terrain
= 1 over an average terrain
= 0.25 over a very rough, mountainous terrain

Microwave Radio
B = factor to convert the worst-month probability to an
annual 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
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 parameter
considered when evaluating the performance
of a microwave communications system.
Microwave Radio
Input noise power
KTB N =
N = noise power (watts)
K = Boltzmann's constant (1.38 X 10
-23
J/K)
T = equivalent noise temperature of the receiver
(kelvin) (room temperature = 290 kelvin)
B = noise bandwidth (hertz)
Microwave Radio
B
KT KTB
N
dBm
log 10
001 . 0
log 10
001 . 0
log 10
) (
+ = =
For a 1-KHz bandwidth at room temperature
( )
B N
dBm
x
N
dBm
log 10 174
174
001 . 0
290 ) 10 38 . 1 (
log 10
) (
23
+ ÷ =
÷ = =
÷
Microwave Radio
Minimum receive carrier power
dBm dBm dB N
N
C
C 80 ) 104 ( 24 min ÷ = ÷ + = + =
Minimum transmit carrier power (Pt)
dBm dBm dB C G P
S t
35 . 33 ) 80 ( 35 . 113
min
= ÷ + = + =
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 bandwidth
of the receiver).
Signal-to-noise ratio (S/N)
- A postdetection (after the FM demodulator)
ratio.
Microwave Radio
Noise Factor and Noise Figure

Noise factor (F) and Noise figure (NF)
- These are figures of merit used to indicate
how much the signal-to-noise ratio deteriorates
as a signal passes through a circuit or series of
circuits.

Noise factor
- a ratio of input signal-to-noise ratio to
output signal-to-noise ratio.
Microwave Radio
Noise factor
) (unitless
ratio noise to signal output
ratio noise to signal input
F
÷ ÷ ÷
÷ ÷
=
Noise figure
F NF
dB
ratio noise to signal output
ratio noise to signal input
NF
log 10
) ( log 10
=
÷ ÷ ÷
÷ ÷
=
Microwave Radio
- Noise figure indicates how much the signal-to-noise
ratio deteriorates as a waveform propagates from the
input to the output of a circuit.
Microwave Radio
Thermal noise
- Most predominant noise.
- Generated in all electrical components
Microwave Radio
Total noise factor of several cascaded amplifiers
3 2 1 2 1
3
1
2
1
1 1 1
A A A
F
A A
F
A
F
F F
n
T
÷
+
÷
+
÷
+ =
FT = total noise factor for n cascaded amplifiers
F1 = noise factor, amplifier 1
F2 = noise factor, amplifier 2
F3 = noise factor, amplifier 3
Fn = noise factor, amplifier n
A1 = power gain, amplifier 1
A2 = power gain, amplifier 2
A3 = power gain, amplifier 3
Microwave Radio
T dB T
F NF log 10
) (
=
In
Out
A1
F1
A2
F2
A3
F3
An
Fn
Total noise figure
Microwave Radio
B KT N
e d
=
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)

Microwave Radio
) (
e o
e o
d i o
T T AKB N
B AKT AKTB N
and AN AN N
+ =
+ =
+ =
( )
( )
T
T
T
T T
AKTB
T T AKB
AN
N
N
S
A
N
S
N
S
N
S
F
e e e
i
o
out
i
out
in
T
+ =
+
=
+
= =
|
.
|

\
|
= = 1
) (
Signal
in
Signal
out
N
O

N
i

T
N
d
T
e

A
Noise figure as a function of
temperature
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 media
and tower.
4. Development of path profiles to determine tower
heights.
5. Link budget calculations.
6. Making path surveys.
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 necessary
operational parameters.
8. Equipment configuration to achieve the most
economical fade margin set in step 5.
Microwave Radio
The K-factor:
- This is a numerical figure that considers the
non-ideal condition of the atmosphere resulting
to atmospheric refraction that causes the ray
beam to be bent toward the earth or away from
the earth.
o
e
r
r
radius earth True
radius earth Effective
k = =
Microwave Radio
k=1
k>1
K<1
Path length
The K-curve
Microwave Radio
Effective Earth Radius (re)
) 005577 . 0 (
) (
04665 . 0 1
S
N
o
km e
e
r
r
÷
=
NS = Surface refractivity
r
o
= true earth radius (6370 km)
) (
1057 . 0
S
h
O S
e N N
÷
=
h
S
= height of potential site in km
Microwave Radio
K-curve conditions:
a.Sub-standard condition
1 < k
- the microwave beam is bent away from the
earth. It is as if the earth’s curvature is extended or
the earth bulge is effectively increased hence, the path
is shortened and the tower must be increased.

Microwave Radio
b. Standard condition
3
4
= k
Under this condition, the fictitious earth
radius appears to be longer than the true earth’s
radius, thus, the earth path is assumed to be smooth
(no obstacles besides mid-path earth bulge) such that
the microwave beam is neither bent toward the earth
or away from the earth.

Microwave Radio
c. Super-standard condition
3
4
> k
This condition results in an effective
flattening of the equivalent earth’s curvature and
the microwave beam is bent toward the earth, which
allows decreasing the tower heights.
Microwave Radio
d. Infinity condition (Flat earth condition)
· = k
This condition results to zero curvature (as if
the earth is very flat) and the microwave beam
follows the earth’s curvature.
Microwave Radio
Earth Bulge (e
b
)
- This is the height at which an obstacle along
the path is further raised due to the earth’s curvature.
75 . 12
5 . 1
) ( 2 ) ( 1
) (
) ( 2 ) ( 1
) (
Km Km
m b
mi mi
ft
b
d d
e
d d
e
=
=
Microwave Radio
Fresnel Clearance
- Another factor that must be added to the
obstacle height to obtain an overall effective obstacle
height.
- It derives from EM wave theory that a
wavefront has expanding properties as it travels
through space.

Fresnel Zone Radius
- The amount of additional clearance that must
be allowed to avoid problems with the Fresnel
phenomenon.
Microwave Radio
) ( ) (
) ( 2 ) ( 1
) ( 1
) ( ) (
) ( 2 ) ( 1
) ( 1
3 . 17
1 . 72
km GHz
km km
m
mi GHz
mi mi
ft
D f
d d
F
D f
d d
F
=
=
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 and
when 60% of the first Fresnel radius clears a path obstruction
in microwave systems.
Microwave Radio
Higher Fresnel Zone Radius
n F F
n 1
=
n = nth Fresnel zone
Microwave Radio
Microwave Link Budget Calculations
Path Profile
- This is a graphical presentation of the path
traveled by the radio waves between the two ends of
the 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
1. Transmit Parameters
a. Transmit Power (dBw, dBm)
b. Transmitter Transmission Line Loss (dB)
c. Transmitter Antenna Gain (dB)
ft GHZ
dB
T
m GHz
dB
T
T
D f G
D f G
D D
G
log 20 log 20 5 . 7
log 20 log 20 8 . 17
6
) (
) (
2 2
+ + =
+ + =
|
.
|

\
|
=
|
.
|

\
|
=
ì ì
t
q
Microwave Radio
d. Effective Isotropically Radiated Power (EIRP)
- The actual power going into the antenna
multiplied by its gain with respect to an isotropic
radiator.
) ( ) ( ) ( dB T dBw T dBw
t t
G P EIRP
G P EIRP
+ =
=
) ( ) ( ) ( ) ( dB T dB T dBw T dBw
T
T T
L G P EIRP
L
G P
EIRP
÷ + =
=
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 the
same antenna-transmitter combination.
dB ERP EIRP 14 . 2 + =
Microwave Radio
2. Path Parameters

a. Free Space Loss
b. Fade Margin
dBm dBm dBm
dBw dBw dB
IT RSL FM
FMIT RSL FM
f ormulas additonal
÷ =
÷ =
) (
) (
:
c. Isotropic Receive Level (IRL)
Microwave Radio
3. Receive Parameters
a. Receiver Antenna Gain (dB)
b. Receiver Transmission Line Loss (dB)
c. Carrier-to-Noise Ratio (C/N)
dB dBm
dB
N RSL
N
C
÷ =
|
.
|

\
|
) (
d. Receiver Sensitivity
Microwave Radio
4. Miscellaneous Parameters
a. Net Path Loss (NPL)
b. Receive Signal Level (RSL)
c. Noise Threshold
dB dBm
dB dBm
dB dBw
dB dBw
NF B N
or
NF
mW
kTB
N
NF B N
or
NF kTB N
+ + ÷ =
+ =
+ + ÷ =
+ =
log 10 174
1
log 10
log 10 204
log 10
) (
) (
) (
) (
Microwave Radio
d. FM Improvement Threshold (FMIT)
dB N FMIT
dB dB
10
_) ( _) (
+ =
Microwave Radio
Reliability
% 100 ) 1 ( x outage R ÷ =
For multi-hop link
n S
xR xR xR R R ...
3 2 1
=
Outage = the amount of time that the
requirements will not be met
R1, R2, …Rn = individual reliability
Microwave Radio
Availability
- the percentage of time a system or link meets
performance requirements
MTTR MTBF
MTBF
A
+
=
MTBF = mean time between failures
MTTR = mean time to repair
Microwave Radio
Unavailability
- the percentage of time a system or link does
not meet requirements

% 100 ) 1 ( x A U
MTTR MTBF
MTTR
U
÷ =
+
=
Microwave Radio
Passive Repeaters
a. Back-to-back Parabolic Antenna Repeater or
Back-to-back Horn Antenna Repeater
- consists of two parabolic antennas
or horn antennas connected back-to-back
through a short piece of waveguide
- this is relatively inefficient, seldom
used except in extremely short paths
Microwave Radio
b. Billboard Repeater
-flat, metal-type reflector, which acts as a microwave
mirror that reflects EM waves surfaces of adequate
flatness is highly efficient (close to 100%)
Microwave Radio
Gain of Billboard Repeater
Thank you!