Aerospace & Defense Technology - December 2022 - 25

RF & Microwave Technology
One example of these radar systems is
used to alert pilots to any hostile or foreign
radar activity and whether they are
being " painted " by the radar of a friend
or foe. This can be accomplished with
both primary and secondary radar systems.
A primary radar system transmits
pulsed RF power and receives backscatter
data that is used for tracking, surveillance
and weather. In contrast, a secondary
radar system transmits RF
signals at one frequency, which is
received by an antenna and decoded,
and then responds on a different frequency.
In addition to performing
friend-or-foe identification using 1030
Megahertz (MHz) and 1090 MHz frequencies,
secondary radar systems can
be used for distance-measuring equipment
using the 960 MHz to 1090 MHz
frequencies, and general communications
using transponders.
RF PAs are also needed for a new
generation of mmWave 5G communications
solutions that, by virtue of
their speed, ultra-wide bandwidth, and
low latency for broadband communication,
will substantially increase how
much information can be shared in
support of real-time decision-making
and other military applications. 5G
systems operating in wide bandwidths
have been vulnerable to high-power
jamming signals, but jammers will
now have to move into the mmWave
range for these close-range 5G-based
systems. Examples include battlefield
sensor networks for command-and-control
data gathering, and augmented
reality displays that enhance situational
awareness for pilots and infantry
soldiers (Figure 2).
5G will also enable virtual reality
solutions for remote vehicle operation
in air, land, and sea missions. Off the
battlefield, 5G will enable a variety of
smart warehouse, telemedicine, and
troop transportation applications.
Each of these applications requires
high-performance power technology
to meet the high-speed data rates
required for video and broadband
data. RF PA suppliers have had to balance
a mixture of conflicting requirements
in order to increase performance
from one end of the transmission path
to the other.
Satellite/Radar/ Military/Point-to-Point
GHz 12 4
c
8
x
12
Lks
Ku
18
25
Ka
5G mmWave = 24,28 and 39 GHz
Figure 2. Frequencies for military and 5G applications.
Component
LNA
PA
Prescalers
Wideband Switches
Key parameterKey Benefit
Noises Figure (dB)
OIP3 (dBm) & Pidb (dbm)
Phase Noise (dBc) @ khz
offset
Low Loss (dB) / High Isolation
(db)
Improved Range/Signal
Sensitivity
Linear/Power - Low
Distortion
Low Noise Floor - More
Range
Low Harmonics in system
Figure 3. Key figures of merit used in military components for satellite communications, radar systems
and 5G networks.
RF PA Requirements Vary by
Application
Defense and aerospace applications
operate in different frequency bands
(Figure 2). Satellite communications for
LEO and geosynchronous communication
operate in the K band, which spans
from 12 GHz to 40 GHz. Radar systems
operate in the 1 GHz to 2 GHz L band
for applications including " identify
friend or foe, " distance-measuring
equipment, and tracking and surveillance.
S band (2 GHz to 4 GHz) is used
for selective response Mode S applications
and for weather radar systems. X
band (8 GHz to 12 GHz) is used for
weather and aircraft radar, while C band
(4 GHz to 8 GHz) is used for 5G and
other sub-7 GHz communications applications.
5G mmWave provides the
highest bandwidths and data rates of
these applications, operating in the 24
GHz and higher frequency bands.
Each application also has different
needs. For instance, one of the critical
figures of merit for 5G applications is
the PA's linear output power. Power
density must be as high as possible
across a broad frequency range. The
table in Figure 3 shows the key points of
merit used in components for today's
Aerospace & Defense Technology, December 2022
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existing and emerging aerospace and
defense applications.
One of the biggest PA requirements is
that it can operate in its linear region
where distortion products are minimal.
This increases complexity, cost, size and
weight though, since more gain stages
are then required to offset the reduction
in RF output power that can be delivered
in this region. Even then, gain distortion
can come into play. Also known
as AM/AM and AM/PM distortion, it
describes the output phase variation
against input power and is often caused
by a PA's nonlinear capacitors. This
occurs when the PA is operated near or
even beyond its saturation point to
maximize conversion efficiency and
generate as much power as possible,
which leads to device nonlinearities
and a compression or peaking of the PA
with input power. Compensation is
required using techniques like digital
predistortion.
Developers face another flavor of distortion
with satellite communications
systems that use higher-order modulation
schemes. This includes 64/128/256
Quadrature Amplitude Modulation
(QAM), which is extremely sensitive to
non-linear behavior. Another challenge
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Aerospace & Defense Technology - December 2022

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