On-Board Internal RF Calibration Electronics for Space-borne SAR

This paper presents the design and measured results of On-board Internal RF Calibration Electronics comprising of a low power dissipation Calibration Switch Matrix realized using hermetically sealed MMIC based Single Pole Double Throw (SPDT) and Single Pole Single Throw (SPST) switches with coplanar waveguide with lower ground plane (CPWG) interconnects and calibration signal distribution network realized using RF power dividers for X-Band Synthetic Aperture Radar (SAR). Calibration signal routing functionality for all antenna beam outputs, individual High Power Amplifier (HPA) outputs, individual Front-end Low Noise Amplifiers (LNA) of all antenna beams as well as the chirp (replica) has been realized by configuring a 3x2 Calibration Switch Matrix comprising of 2 inputs, 1 output and 1 bidirectional port. This multi-facet on board calibration scheme is required in SAR payloads to know the actual differential phase and amplitude variations across the transmit and receive modules, the actual imbalances of the antenna beams and having a reference chirp (replica) data required for pulse compression. The main and redundant switch matrix units are stacked with its respective Electronic Power Conditioning (EPC) unit and cross patching power dividers in a three-tier stack. Excellent isolation between desired and undesired signal along all paths has been achieved with the switches consuming a power of only 160mW. A low power dissipation, high isolation X-Band switch matrix, required for On-board Internal RF calibration electronics, has been designed, realized and successfully delivered for three satellite constellation of 8-beam reflector based SAR.