Spillover Analysis and Mainbeam Characterisation of Arctic Weather Satellite Radiometer Using Method of Moments

The Arctic Weather Satellite (AWS) is a single instrument mission consisting of a microwave sounder operating in the 54, 89, 183 and 325 GHz bands. The optical design of the instrument consists of a feedcluster directly illuminating a crosstrack scanning mirror, keeping the instrument compact. Due to the simple optics, the beams are not co-aligned and none are in the scanning mirror focal point, leading to beam divergence, asymmetry and scan angle dependent variations in spillover. Using Method of Moment (MoM) simulations of the optics as well as instrument structure, the complete farfield sphere of the instrument can be simulated up to 183 GHz. This paper contains detailed analysis of spillover, beam divergence and intercomparison of physical optics, MoM and nearfield antenna measurements for the mainbeam.