Planar Orthomode Transducer Based on Effective Polarization-Independent Coupling

Abstract

A planar orthomode transducer (OMT) is introduced and studied based on effective polarization-independent coupling (EPIC). The concept of EPIC is developed on observing the relation between the required coupling length of the TEm mode and that of the TEnr mode in a fused rectangular waveguide coupler. Within a specific band of operation, it is found that the horizontally-polarized T'Eni mode needs twice the longitudinal length required by the vertically-polarized TE10mode in order to achieve a full coupling. Therefore, along a specific coupling length, the TElo mode couples two times back and forth while the TEol mode couples only once. By this concept, a full separation can be achieved between the two orthogonal modes which leads to the desired function of an OMT. This is determined by the dielectric constant of substrate. A full control of the substrate permittivity is achieved by introducing air perforations into the substrate with a pre-specified pattern. Hence, the resultant effective uniaxial medium introduces the required parameters.