Would it be worthwhile to replace the TWTA Transmitter power amplifier in the Lynx RF front end? If one were designing a replacement radar would GaN be the best solution? The Lynx Radar requires a long pulse high duty factor with flat response over a wide band at Ku band in order to achieve high resolution imagery at moderate range. Sandia designed the radar in the mid 1990's, when TWTA was the only solution. In the UAV application space, weight, power, and reliability are at a premium, which make a solid state solution attractive. It is not clear that GaN is up to the challenge yet.
Sandia spie99_paper Lynx SAR/GMTI Radar
Lynx is a high resolution, synthetic aperture radar (SAR)
that has been designed and built by Sandia National Laboratories in collaboration
with General Atomics (GA). Although Lynx may be operated on a wide variety of
manned and unmanned platforms, it is primarily intended to be fielded on
unmanned aerial vehicles. In particular, it may be operated on the Predator, I-GNAT,
or Prowler II platforms manufactured by GA Aeronautical Systems, Inc.
The Lynx production weight is less than 120 lb. and has a
slant range of 30 km (in 4 mm/hr rain). It has operator selectable resolution
and is capable of 0 .1 m resolution in spotlight mode and 0.3 m resolution in
strip map mode. In ground moving target indicator mode, the minimum detectable
velocity is 6 knots with a minimum target cross-section of 10 dBsm. In coherent
change detection mode, Lynx makes registered, complex image comparisons either
of 0.1 m resolution (minimum) spotlight images or of 0.3 m resolution (minimum)
strip images.
The front-end microwave components include a TWTA capable of outputting peak power of 320 W at 35% duty factor (105 W average) averaged over the Lynx frequency band (16.7 GHz +/- 1.5 GHz) and a Low Noise Amplifier LNA that allows an overall system noise figure of about 4.5 dB.
GaN Amplifiers Challenge TWTAs | Active components content from Microwaves & RF
For fans of solid-state power,
API Technologies Corp.
is unveiling a new line of gallium-nitride (GaN) power amplifiers at
Booth No. 1515 at the 2014 IMS. With frequency coverage to 18 GHz and
power levels to 1 kW, these pulsed amplifiers offer the power levels of
traveling-wave-tube amplifiers (TWTAs) at a fraction of the size and
weight. They are ideal for commercial and military applications,
including radar, communication transmitters, and jamming systems. The
amplifiers are supplied in hermetic housings and available with a
variety of options, include sleep mode, blanking, forward/reverse power
detection, discrete power supply designs for wide DC input voltage
ranges, as well as microprocessor-based control features for bias
optimization, temperature compensation, and fault monitoring.
GaN Amps Replace TWTAs | Active components content from Microwaves & RF
Designing and building a line of solid-state power amplifiers based on
gallium-nitride GaN) transistors and active devices, Diamond Microwave
offers amplifiers at X- and Ku-band frequencies as alternatives for
traveling-wave-tube amplifiers (TWTAs) in demanding defense, aerospace,
and communications applications. Certified to ISO 9001:2008, the firm
believes that its amplifiers provide excellent pulsed-power performance
with power-to-volume ratio that is among the highest in the industry.
The GaN power amplifiers offer pulsed output-power levels to 150 W and
ae flexible in layout and architecture for a wide range of applications.
The company displayed a Ku-band amplifier at the recent International
Microwave Symposium with peak pulsed output power of 125 W at 16.5 GHz
and 1-dB bandwidth of 1.5 GHz.
Comparison of High Power Amplifier Technologies: TWTAs vs SSPAs
Designers of high power communication systems are constantly
evaluating and debating the merits of using Traveling Wave Tube
Amplifiers (TWTA) and Solid State Power Amplifiers (SSPA) in their
transmitting systems. Most decisions are made on personal preferences
for one technology over another. The reality is that both technologies
have advantages and disadvantages, with higher power levels and higher
frequencies leaning toward the TWTA as a better choice.
...
SSPA and TWTA are both viable alternatives to consider for power
amplification in a satellite earth station, with SSPA the more
advantageous at lower power, i.e. less than 20 watts. At greater power
levels, size, weight, and efficiency become important characteristics
that skew the preferred choice to the TWTA. The following table
summarizes the comparison of a 200 watt SSPA and a 665 watt TWTA, but
this comparison typically can be scaled to other power levels in the
range of 50 watts to 2.5k watts. The TWTA advantage increases at higher
power levels and higher frequencies, where SSPA efficiency decreases.
200 Watt SSPA vs. MCL MT4000 700 Watt TWTA
SSPA
• 200 Watt P1dB
(250 Watts Psat)
• 2800 Watts AC Power
• 7.1% Efficient
MCL MT4000
• 665 Watt Psat (Equivalent to SSPA 222 Watts)
• 2400 Watts AC Power at Psat (27.8% Efficient)
• 28% Efficient at Psat
• Back-Off (Usually Mode of Operation)
• 1650 Watts TWT vs. 2800 Watts SSPA
• TWTA uses 40% less power
TWT vs. SSPA Comparison
• MT4000 is 10% higher equivalent power
• Typically uses 41% less power
• 266% more available power
• Smaller size (24" vs. 28" length)
New and Exciting GaN-based Solid State Power Amplifiers & Converters | Advantech Wireless
GaN based SSPAs are opening completely new market opportunities for
Satellite based Communications with unmatched performance, high
reliability and low OPEX. Within the same footprint, GaN allows us to
double the RF power and reduce energy consumption by up to 70%! In
addition, GaN exceeds by several orders of magnitude the performance of
previous generation of SSPAs based on LDMOS or GaAs technology.
GaN The TWT Killer Not So Fast
Gallium nitride’s (GaN) meteoric rise to darling of the RF design
industry has been accompanied by some lofty predictions. One such claim
is that the emergence of GaN solid-state semiconductors means certain
death for traveling wave tube (TWT) technology. As it turns out, GaN
might not replace TWTs after all, at least not for the foreseeable
future. Although GaN has captured market share from TWTs in some
lower-power, lower-frequency applications, there is much evidence
suggesting TWT technology is alive and well.
