High Power Ka-Band Solid State Amplifier

A Ka-band, high-power, solid-state amplifier has been developed as a direct replacement unit for a TWT in an EHF satellite communications earth terminal. The two-stage amplifier uses silicon double-drift IMPATT diodes and waveguide cavity power-combining techniques to provide 6.2 W of RF output power at an operating frequency of 36.815 GHz. The l-dB injection-locking bandwidth is 270 MHz at the 31 dB gain point. The DC-to-RF efficiency is 5% and the RF combining efficiency is 70%. The design requires 1 W, Ka-band IMPATT diodes and is configured as a two-stage amplifier. The first stage is a single-diode driver module and the second stage is an eight-diode combiner module. The driver and combiner are mounted on two junctions of a low-loss, wideband, five-junction circulator. Three junctions are terminated and provide input, interstage and output isolation. The solid-state amplifier is compact (5x8x4 in.), relatively lightweight (7.3 lbs.), requires a 60-V, 3-A DC power supply. Amplifiers such as this should have median time to failure of ≫3x10⁴ hours based on reliability studies performed on diodes and components similar to those used.