Analysis of the Annular-Ring-Loaded Circular-Disk Microstrip Antenna

A rigorous analysis of the natural resonance frequencies and input impedance characteristics of an annular-ring-loaded (ARL) circular-disk microstrip antenna is presented. Using vector Hankel transforms (VHT), the problem is formulated in terms of vector dual-integral equations. Galerkin's method is then used to solve the equations to obtain the resonance frequencies and the current distributions on the conductive patches arising from a probe excitation. Due to the singular nature of the current distribution, the singularity subtraction method has been used to accelerate the convergence of basis function expansions. Experiments for determining resonance frequencies and input impedance characteristics of an ARL circular-disk microstrip antenna with various substrate thicknesses have been made. The theoretical results are in good agreement with the experimental data even when the thickness of the substrate is 0.1 substrate wavelength. It is shown that this theory can be used to analyze some microstrip antennas with an electrically thick substrate, including mutual coupling between conductive patches or between the patch and the feed of a microstrip antenna.