Hybrid High Power Amplifiers for L-Band Space Application

This paper describes the design and implementation of 2 hybrid high power amplifiers at L band for a space application. Indeed, the amplifiers represent prototype test vehicles for a larger hybrid amplifier to be used as the final power stage in the transmitting chain of a T/R module of an L-band SAR antenna for earth observation. The amplifiers described in this paper exploit a discrete bar of a commercial 0.35 mum pHEMT process as active device. The first amplifier, featuring a single discrete device, delivers 12 Watts with 56.5% PAE and 12.3 dB gain at 2 dB compression. The second amplifier exploits 4 discrete pHEMT bars using input/output microstrip splitter/combiner and lumped wire bonding/ceramic MIM capacitor output matching networks. It delivers 42 watts with 50% PAE and 13 dB gain at 2.5 dB compression. Since it is a space application, these performances have been achieved with the required de-rating on break-down voltages, current densities and operating channel temperature. The latter has been evaluated by means of a 3-D device model implemented in the framework of a finite differences numerical thermal simulator. In spite of the constraints due to space de-rating rules, the obtained output power densities are 1 W/mm and 0.875 W/mm for the single-discrete and the 4-discrete amplifiers, respectively, which represent a value very close to the state of the art for pHEMT processes.