A UHF 1-kW solid-state power amplifier for spaceborne SAR

A 2-stage 40 dB gain 1 kilowatt transmitter pallet for remote sensing synthetic aperture radar (SAR) applications in P-band from 420 to 450 MHz is presented. The unique feature of this paper is the use of GaN transistors operating from a 75 V drain bias. All commercially-available GaN transistors operate from 60 V or less drain supply, but using 75 V increases the load impedance at the fundamental and reduces the output capacitance which enables the optimum impedance to be presented to the FET at the harmonics even at kW power levels. As a consequence, we report 75% minimum power-added efficiency from a two-stage amplifier across the entire 420-450 MHz bandwidth under 100 μs with 10% duty cycle. This is 15% higher efficiency than is typically achieved with traditional TWT implementations.