Full Bandwidth Calibration of RISAT-1B Active Array Antenna using Near Field Chirp Acquisitions

This paper reports the Near-field based methodology to calibrate amplitude and phase responses of phased array antenna for RISAT-1B SAR payload. The unique feature of this methodology is utilization of chirp signal generated within the payload. Usually, after integration of SAR system, antenna ports are not accessible for connection of any additional measurement setup. Presented calibration procedure eliminates this requirement by utilizing payload generated chirp signal and receiver through test ports. Chirp signal along with pulse compression technique enables broadband calibration over complete system bandwidth. Equalization of phases and amplitudes across the phased array antenna is carried out by applying necessary corrections counts at DA and DPS of TRMs. The derived corrections are validated through measurement of antenna holograms and respective far-field antenna patterns.