Pulse coded calibration of the sentinel-1 SAR phased array antenna optimised for low active return loss

The Sentinel-1 satellite carries on board a C-band Synthetic Aperture Radar built from 560 active radiating waveguide arrays. The 280 horizontally polarised waveguide arrays and the 280 vertically polarised waveguide arrays are arranged as dual-polarised pairs in sufficient proximity to allow for grating lobe free electronic steering of the S-1 SAR antenna in the elevation plane. Each waveguide array is connected to a transmit-receive module (TRM) feeding or receiving signals via their common antenna port. The SAR instrument has an internal RF Characterisation mode exploiting the phase shifting capabilities of the TRMs, that allows monitoring of the individual excitations of each waveguide array in both Tx and Rx. The present paper reports on a novel Pulse Coded Calibration (PCC) scheme, that whilst maintaining some salient features of the Hadamard based PCC, also allows to optimise the antenna active return losses. A low active return loss is beneficial to minimise the RF stress of the TRM output circuitry and improves the accuracy of the RF Characterisation itself.