Slot-Array Antenna Feeder Network for Space-Borne $X$ -Band Synthetic Aperture Radar

This paper studies the concept of a new waveguide feeding technique for wideband application of an X-band deployable rectangular parallel-plate slot-array antenna panel network with the vertical polarization for a synthetic aperture radar onboard a 100 kg class microsatellite. The antenna design procedure in high-frequency structure simulator followed by its fabrication and measurement results are explained. Simulations and antenna array measurement results confirmed that the corporate feeding technique achieved wide-beam antenna gain within permissible reflection limit in the desired bandwidth, thereby ensuring wideband operation. The fabricated center antenna panel achieved 35.3 dBi peak gain and 75% peak aperture efficiency, and the four-panel antenna array network achieved 40.8 dBi peak gain and 68% peak aperture efficiency in designed 300 MHz bandwidth. Although there was some mismatch in the measured reflection profile of each panel compared to the simulation results, this discrepancy was subsequently analyzed to be due to the imperfect modeling of the adhesive layer thickness and further analysis revealed that increasing the slot length of all coupling slots in the waveguide feeders by 0.2 mm can nullify this undesired effect.