Scanning Impedance of Proximity-Coupled Rectangular Microstrip Antenna Arrays

摘要

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 percent 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 report presents an infinite array analysis that is applied to three types of proximity-coupled rectangular microstrip elements. The spectral dyadic Green's function for a two layer rounded dielectric slab is used do 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 described. Theoretical results are presented for scanning input impedance as a function of substrate parameters, array spacing, and element geometry.