SAR antenna beam pattern optimisation

The SAR system design process can become a complex task, in particular if active phased array antennas are involved. The inherent flexibility due to amplitude and phase settings in the transmit/receive modules allows individual beam pattern pointing and shaping. For SAR, this flexibility is mainly used in the elevation direction, i.e. across track, over the total range of incidence angles. Usually, the criteria for the optimised antenna elevation beam pattern are the overall system performance requirements as, for example, the ambiguity ratio, the radiometric accuracy, and the noise equivalent sigma zero. The range ambiguity ratio can be controlled by appropriate antenna sidelobe suppression at defined positions in the elevation pattern. The gain slope in the beam main-lobe is linked to the radiometric accuracy via pointing errors. Finally the antenna peak gain should be maximised for best noise equivalent sigma zero performance. Optimisation of the beam pattern for best system performance becomes complex, since various sets of amplitude and phase settings might fulfil the requirements. In order to support this complex task, the SAR Performance Modelling Software Package 'NextPerf' has been enhanced by trading the above system performance requirements with respect to the antenna elevation beam pattern.