JED - August 2014 - 37

TECHNOLOGY SURVEY

A SAMPLING OF SOLID-STATE POWER AMPLIFIERS
By Ollie Holt

J

ust a few months ago JED published a survey on
MPM's and TWT power amplifiers. That survey's
introduction mostly discussed methods of combining solid-state power amplifiers in order to
obtain around 100 Watts of output power. The
advantages of solid-state power amplifiers are
lower operating voltages and higher reliability. The disadvantages of solid-state are lower efficiency than TWT
power amplifiers and, of course, lower output powers. The
combining methods discussed in that survey can be used
with Gallium Nitride (GaN) power amplifiers to achieve
similar powers.
GaN was originally used in Light Emitting Diodes (LEDs).
It has a wide band gap of 3.4 eV, which makes it suitable
for optoelectronic applications. This also makes it useful
in high-power and high-frequency devices, such as power
amplifiers for electronic warfare (EW), communications
and radar systems. GaN devices have a low sensitivity to
ionizing radiation, making them a suitable material for
military and space applications, which require high stability in radiation environments. GaN transistors also operate
at much higher temperatures and at higher voltages than
other solid-state transistors; they make ideal power amplifiers at microwave frequencies.

THE SURVEY
This month's survey covers solid-state power amplifiers
(SSPAs) - both SSPA "systems" and SSPA modules - for military EW, radar and communications applications. (JED will
cover other amplifier technologies, such as GaN transistors
and low-noise amplifiers, in future surveys.)
In the table, the "operational frequency range" defines
the lower to upper frequency range of the GaN Power Amplifier product listed.
The output power defines the maximum output power expected at the maximum gain. Gain defines the increase in
power that can be achieved from the input to output. Typically you just multiply the input power by the gain to determine the output power if the amplifier stays linear. Typically
a power amplifier stays in the linear operating mode as long
as the maximum input power limit is not exceeded. If the
maximum input power is exceeded, then the output power
will no longer be equal to the gain times the input power.
The amplifier becomes non-linear and output power starts to
flatten around the maximum output power value.
In the "harmonic and spur levels" column, dBc or dB relative to the carrier is a measure of how much higher the carrier signal is with respect to harmonics or spurious signals

GaN has seen wide use in IED jammer applications.
(US Army photo)

created within the device. For most applications, the larger
this value is the better the performance. Also note that
when the input power exceeds the maximum, the amplifier
will start operating in the non-linear mode and the harmonics and spurious signals will continue to increase in output
power, but the signal will not until signal output power and
spurious output power are equivalent.
Efficiency is defined as power added efficiency (PAE),
which is the output power (RF) minus the input power (RF)
divided by the DC power. In high-gain systems, the results
are about the same as efficiency (output power [RF] divided
by input power [DC]). In low-gain systems, however, the efficiency can be very different. Also take note that in the
survey the input power (DC power) is average power input.
For a pulsed system PAE is calculated using the input power
(DC) when the pulse is created. It is not the average input
power (DC).
As SSPA technologies (particularly GaN) have improved
over the past decade, so the number of applications has
grown from radios and RCIED jammers, to radar, radar jamming and SATCOM. The number of companies in the SSPA
market has grown significantly, as well. JED identified more
than 30 SSPA manufacturers serving the defense market.

JED's September survey will cover communications
jammers and RCIED jammers.

37



JED - August 2014

Table of Contents for the Digital Edition of JED - August 2014

The View From Here
Conferences Calendar
Courses Calendar
From the President
Letters
The Monitor
Washington Report
World Report
Back to the Future With HF SIGIHT
HF SIGIHT Battles the Ionosphere
Technology Survey: Solid-State Power Amplifiers
Book Reviews
EW 101
Index of Advertisers
JED Quick Look
JED - August 2014 - cover1
JED - August 2014 - cover2
JED - August 2014 - 3
JED - August 2014 - 4
JED - August 2014 - 5
JED - August 2014 - The View From Here
JED - August 2014 - 7
JED - August 2014 - Conferences Calendar
JED - August 2014 - 9
JED - August 2014 - Courses Calendar
JED - August 2014 - 11
JED - August 2014 - From the President
JED - August 2014 - 13
JED - August 2014 - Letters
JED - August 2014 - The Monitor
JED - August 2014 - 16
JED - August 2014 - 17
JED - August 2014 - 18
JED - August 2014 - 19
JED - August 2014 - 20
JED - August 2014 - 21
JED - August 2014 - Washington Report
JED - August 2014 - 23
JED - August 2014 - World Report
JED - August 2014 - 25
JED - August 2014 - 26
JED - August 2014 - 27
JED - August 2014 - Back to the Future With HF SIGIHT
JED - August 2014 - 29
JED - August 2014 - 30
JED - August 2014 - 31
JED - August 2014 - HF SIGIHT Battles the Ionosphere
JED - August 2014 - 33
JED - August 2014 - 34
JED - August 2014 - 35
JED - August 2014 - 36
JED - August 2014 - Technology Survey: Solid-State Power Amplifiers
JED - August 2014 - 38
JED - August 2014 - 39
JED - August 2014 - 40
JED - August 2014 - 41
JED - August 2014 - 42
JED - August 2014 - 43
JED - August 2014 - 44
JED - August 2014 - Book Reviews
JED - August 2014 - EW 101
JED - August 2014 - 47
JED - August 2014 - 48
JED - August 2014 - Index of Advertisers
JED - August 2014 - JED Quick Look
JED - August 2014 - cover3
JED - August 2014 - cover4
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