Broad-band wide-angle quasi-optical polarization rotators

A quasi-optical and wide-angle (of incidence) polarization rotator is described and analyzed. It consists of three or more parallel, equispaced wire-grid polarizers whose wires are oriented in different directions. With the proper choice of the number of grids, their spacings, and their relative orientations, such a polarization rotator is capable of operating over a broad frequency band and a wide range of angles of incidence. A seven-grid 90 deg polarization rotator was designed to operate over a 42% relative bandwidth for a + or - 60 deg range of angles of incidence with less than 0.1 dB transmission loss. Various designs based upon this analysis are given. The impetus for this work is the specific application of this polarizer in a dually polarized multibeam satellite ground station antenna employing a linear array feed. The design of a seven-grid polarization rotator for the ground station antenna is presented.