Abstract

T/R modules suitable for spaceborne SAR instruments have to fulfil very strong requirements given by the challenging environmental and electrical conditions in space. This paper shows that the HBT (Heterojunction-Bipolar-Transistor) technology is able to meet these requirements for future SAR systems. For this application a separate breadboard Tx-chain as well as a T/R module have been realised which operate in X-Band and use the HBT technology for the high power chain. For the breadboard Tx-chain with driver and HPA in balanced configuration an output power of 39.5 dBm with an efficiency of 32.5% at 10% duty cycle was achieved. For the medium power T/R module with HBT driver and HPA in single ended configuration the output power is stabilised by a power control loop to 35 dBm with an overall module efficiency of better than 11.5% at 10% duty cycle. Full amplitude and phase stability of the T/R module is realised by a phase stable variable gain amplifier (VGA) and a 7-bit phase shifter. An accuracy of ± 0.5 dB in Rx gain and ± 6° in Rx/Tx phase under all operating conditions has been achieved by a novel and highly flexible calibration method. The paper will discuss the T/R module architecure with emphasis on the Tx-chain with HBT-amplifiers (fabricated at UMS) and the realised concept for the power control loop. Furthermore the T/R module performance will be presented with respect to SAR system requirements.