Citation/Abstract

Conventional microstrip antenna feeding techniques using microstrip transmission lines or coaxial probes limit the bandwidth to a few percent due to feed radiation and reactive mismatch. Proximity-coupled feeds can be used as an alternative to direct contact feeds on thick substrates by coupling to an embedded microstrip line or by stacking several patches. Proximity coupled element bandwidths of up to 25% have been achieved with single patch elements, but no models presented thus far can predict the effects of inter-element coupling upon resonant frequency and bandwidth. This paper presents an infinite array analysis which is applied to three types of proximity coupled rectangular microstrip elements. The spectral dyadic Green's function for a two layer grounded dielectric slab is used so that all surface wave and mutual coupling effects are included. A method of moments with three types of expansion modes is used to efficiently solve for the unknown current distribution, and a model for microstrip traveling wave feed lines in an infinite array is described. Theoretical results are presented for scanning input impedance as a function of substrate parameters, array spacing, and element geometry. Experimental data from a waveguide simulator and an 11 x 11 array are shown to validate the analysis.