Improved Matching of Waveguide Focal Plane Arrays Using Patch Array Covers as Compared to Conventional Dielectric Sheets

This paper presents the advantages of microstrip patch array covers as matching layers for waveguide arrays, as compared with the use of conventional dielectric sheets. It will be demonstrated that both types of covers can be tuned to improve the transmission levels of uncovered arrays at either low frequencies or over a very wide band. However, at low frequencies where the radiation performance tends to be poor due to strong mutual coupling between closely separated elements, the patch array cover offers itself as a lower profile and lighter weight matching structure. This makes it highly advantageous for use in space applications and satellite communications. In addition, it is also able to provide wider matching bandwidths than dielectric sheets. Here, we present a rigorous analysis of such a patch array printed on a dielectric slab and placed over an array of sidewall loaded hard rectangular waveguides. Due to the desirable properties of its aperture field, this type of element serves as an ideal reference for conveying the properties of the two matching layers studied here. Also, to ensure the matching layer performance is independent of the array elements, optimized elements are used in all computations. The method of moments using spectral Green's functions for multilayer structures is employed. Two array operation scenarios are studied, which are the direct radiating phased arrays, and focal plane arrays (FPAs) as feeds for reflectors.