Equivalent circuit model for a waveguide probe with application to DRA excitation

A simple equivalent circuit is used to model an arbitrarily loaded waveguide probe with emphasis on probe-excited dielectric resonator antennas. The values of the lumped inductance and capacitance are obtained via the method of moments analysis for the problem of a short-circuited probe acting as a waveguide scatterer. For problems involving the excitation of an external load, the aperture through which the probe extends to the load is modeled by a shunt capacitance, and an additional transformer is introduced to model the coupling to the load. Expressions for these circuit parameters are obtained using curve-fitting techniques and are employed to determine the lengths and positions of an array of waveguide probes used to feed external loads with feeding currents of desired relative values. The procedure is applied to synthesize waveguide-fed antenna arrays to achieve a specified radiation pattern. The scanning capabilities and the effect of the mutual coupling are studied by comparing radiation patterns obtained from the analysis of the whole array and from the pattern multiplication principle