Full-wave analysis of microstrip-fed slot antennas and couplers.

Abstract

The use of waveguide slots in microwave circuits can be traced back at least as far as the research efforts associated with World War II. They have since been widely used in antenna designs as radiating elements and in feed networks as couplers. Recently, strip-fed slots have become of interest since they are easily integrated with other strip-based structures, are simple to construct using printed circuit techniques, and can readily be made conformal, light-weight and low-cost. Highly accurate analysis and design tools are required to avoid time-consuming empirical techniques and thereby minimize design costs. New requirements include the capability to model multi-layer substrates and superstrates as well as slots which cannot be approximated as infinitely thin. A full-wave space-domain integral equation approach is developed which models these components through the Method of Moments. Exact dyadic Green's functions of both the electric and magnetic type are derived for both electric and magnetic currents. They are presented in a generalized form allowing the representation of multiple layer substrates and superstrates through simple transmission line formulas. Two methods of extracting the equivalent circuit parameters for these components are described. The Standing Wave Method is commonly used because of its simplicity for circuits which have dimensions at least on the order of one wavelength. The Reaction Method is more general but also more complex and can be used for all circuits. Numerical results are shown in relation to experimental measurements to illustrate the characteristics of these component and the validity of the models. The techniques can be applied equally well to other circuits which have no apertures (strips only) as well as those without conducting strips (slots only). Because the exact Green's functions are used, the approach has no limitations with respect to frequency and can therefore be used for a wide variety of applications, from the analysis of coupling in low frequency circuits to the evaluation of radiation from millimeter wave structures.