Aerospace & Defense Technology - December 2022 - 26

RF & Microwave Technolgy
is achieving satisfactory peak-to-average power ratio (PAPR) -
that is, the ratio of the highest power the PA will produce to
its average power. PAPR determines how much data can be
sent, and is proportional to the average power. At the same
time though, the size of the PA needed for a given format
depends on the peak power.
These and other conflicting challenges can only be met with
GaN MMIC PAs, especially for satellite and 5G applications.
GaN MMIC PA Benefits for Ka-Band Satcom Applications
Most of today's LEO satellites operate in the 27.5 to 31 GHz
Ka-band spectrum where they are playing a major role in supporting
the tsunami of traffic being generated by video and
other data-intensive applications. Unlike the traveling-wave
tubes (TWTs) traditionally used as power sources at these frequencies,
GaN offers higher efficiency and much lower operating
voltages. GaN is also ideal for satellites in geosynchronous
orbit that need their inherent radiation tolerance.
GaN-based PAs are also much smaller than TWTs and better
aligned with the needs of active phased array antennas. They
remove any requirement for complex and burdensome power
combiners. They also deliver more RF power in a smaller footprint
than gallium arsenide (GaAs) options, while operating at
higher voltages.
GaN MMIC PA Benefits for Military 5G Networks
The mmWave (24 GHz to 100 GHz) frequency spectrum is
much less congested than lower frequency bands that are
struggling to keep up with the signal traffic from TV, radio,
and current 4G LTE networks operating between 800 and
3,000 MHz. The higher the frequency bands, the more data
can be carried (albeit over much smaller areas). This is what
the military needs in its coming generation of close-range
5G-based systems. The mmWave band can be used to increase
data bandwidth over smaller, densely populated on-battlefield
and off-battlefield networks.
GaN can extend 5G New Radio (NR) femto- and pico-cell
base stations deployments into the mmWave band for these
military applications, where they will deliver the necessary
bandwidth and data rates. Laterally-Diffused Metal-Oxide
Semiconductor (LDMOS) MOSFETs are insufficient at >3.5
GHz. GaAs is incapable of delivering high enough power in
the mmWave band without moving to an extremely large die.
GaN offers the right balance of higher frequencies and power,
wide bandwidth, and the required thermal properties, gain,
low latency, and high switching speeds.
To fully realize their promise though, GaN MMIC PAs also
need silicon carbide (SiC) substrates that improve power density
by enabling MMICs to offer better thermal conductivity
than is possible with silicon-based wafers.
Effects of Adding SiC Substrate
The use of SiC-based substrates improves GaN MMIC PA
power density through better thermal conductivity than is
possible with silicon-based wafers. Additional benefits include
higher wafer yields because of SiC's better lattice match with
GaN, and a 20 percent smaller package size as compared to
LDMOS technology, plus greater efficiencies. Air and spacebased
systems get the optimum combination of high-power
density and yield in the smallest footprint, along with lower
weight, the highest possible power support, superior efficiency,
and support for high-voltage operation with a longevity of
at least 1 million hours at a junction temperature of 255 °C.
Component suppliers are bringing GaN MMIC PAs to market
across more frequency options and more choices of bare
die and packaged MMIC PA products. These offerings, along
with complementary discrete high electron mobility transistor
(HEMT) devices and other components, will give military
system developers new ways to meet the unique needs of
next-generation radar systems, satellite communications solutions,
and 5G mmWave networks. GaN MMIC PAs will help
solve the difficult linearity and efficiency challenges of higher-order
modulation schemes and enable system designers to
bypass the shortcomings of GaAs, LDMOS and TWT-based PAs
so they can reach the necessary gain improvements for aerospace
and defense applications without compromising on
cost, size, weight, complexity or PAPR requirements.
This article was written by Michael Ziehl, Senior Manager of
Product Marketing; and Baljit Chandhoke, Product Manager,
Microchip Technology Inc. (Chandler, AZ). For more information,
visit https://www.microchip.com.
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Aerospace & Defense Technology, December 2022
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Aerospace & Defense Technology - December 2022

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