Development of the Onboard Calibration Target for the Arctic Weather Satellite

We present the design and characterization of the onboard calibration target (OBCT) for the arctic weather Satellite radiometer. The arctic weather satellite (AWS) is a single-instrument mission consisting of a cross-track scanning microwave radiometer. The radiometer optics consists of a feed cluster with four horns (54, 89, 183, and 325 GHz) directly illuminating a primary scanning mirror. The OBCT is a wedge-shaped cavity with an absorber consisting of an epoxy-based mixture, developed and produced by the University of Bern. The coupling into the target via a secondary mirror is simulated using Ticra Tools and the effects of the divergent beams are investigated. We present the development of the target and laboratory measurements of the flight model showing a return loss of 55 dB or better for all bands in TM mode. A worst case thermal simulation is presented, highlighting possible temperature gradients in the target.