Theory and experiment on microstrip antennas

TLDR

The paper discusses peculiar properties arising from degenerate or slightly degenerate eigenvalues in microstrip antennas. The study develops a simple cavity‑model theory to analyze microstrip antennas. The theory provides formulas for numerous canonical microstrip antenna shapes. The theory accurately predicts radiation patterns, impedance loci, and resonant frequencies, with computed results closely matching measurements across many antenna shapes and dimensions, and the input admittance locus follows a nearly constant‑conductance circle shifted into the inductive region.

Abstract

A simple theory based on the cavity model is developed to analyze microstrip antennas. Formulas for numerous canonical shapes are given. In general the theoretically predicted radiation patterns and impedance loci closely agree with those measured for many antennas of various shapes and dimensions investigated thus far. In fact, this theory enables the computation of both patterns and impedance loci with little effort. The input admittance locus generally follows a circle of nearly constant conductance, but its center is shifted to the inductive region in the Smith chart plot. Peculiar properties for the case with degenerate or slightly degenerate eigenvalues are discussed. An accurate formula for determining the resonant frequency of a rectangular microstrip antenna is also given.