Extended cavity model analysis of stacked microstrip ring antennas

Microstrip ring antennas deserve special attention because they can yield a larger bandwidth compared to other conventional patches and outstanding gain-bandwidth characteristics that renders them useful for applications that require reduced size and good radiation efficiency, like in the area of mobile communications. Stacked microstrip ring antennas for dual-frequency behavior and improved bandwidth are studied and analyzed. The cavity model for single microstrip antennas is extended with some modifications for the stacked geometry to account for the coupling between the upper and lower cavities, fringe fields, dispersion effects, and the effective loss tangent of the dielectric material. Green's functions are used to allow for modal analysis and closed-form solutions. The results for the radiation patterns and input impedance predicted through this simple model are compared with experimental data.