Accurate coupling junction models in the design of planar slot arrays

In a waveguide-fed planar slot array, a main waveguide feeds a family of crossed branch waveguides containing radiating slots. Each coupling junction typically consists of a centered-inclined coupling slot and a pair of straddling longitudinal radiating slots, generally located a quarter guide wavelength away in the branch waveguide. In the analysis and synthesis of slot arrays, higher-order mode coupling effects in coupling junctions are not considered. Higher order mode coupling between such slots is expected to be significant. In addition, for some coupling geometries, there are singularities in the Green´s functions for the coupling problem. Ignoring the higher-order mode coupling between the coupling slot and radiating slots may introduce significant errors in the input match condition, and radiation pattern performance of planar arrays. We present a perturbation method to include the higher order mode coupling effects in coupling junctions in the design of a planar slot array.<>