A 48Watt and 60dB Gain Hybrid Power Line-Up for an L-Band T/R Module of a Space SAR Antenna

This paper describes the design, implementation and characterization of an entire transmitting line-up of an L-band T/R module for space application. The module is used in the array of a SAR antenna for earth observation. The entire line-up described in this paper is composed of three stages, namely pre-driver, driver and final-stage HPA, for an overall small-signal gain of 60 dB at 1275 MHz central frequency. The application bandwidth is 80 MHz and the output power of the module exceeds 48 Watts over the bandwidth under pulsed operating conditions (60 μs pulse width at 10% duty cycle). The PAE of the entire line-up is over 43% across the bandwidth. A 0.35-μm gate length GaAs pHEMT process has been used for the design of the three stages: the pre-driver is a 2-stage monolithic circuit with external drain bias chokes, while both the driver and the final HPA are hybrid circuits, which exploit a 15-mm gate width power bar designed with internal stabilization and pre-matching distributed structures. Microstrip structures on alumina, gold bonding wires and custom-designed ceramic MIM capacitors have been used for lumped and distributed matching and combining networks. Gold wire coils are exploited as bias chokes. The entire line-up is very compact for L-band: with all bias networks and stabilizing capacitors included, it takes up a space of 36x30 mm within the T/R module.