Accurate model for the input impedance of coax-fed rectangular microstrip antenna with and without airgaps

A simple and numerically efficient model for the input impedance of a rectangular microstrip antenna with and without an airgap between the substrate and the ground plane is presented. This airgap does not significantly alter the relative field pattern but it does provide a simple parameter by which the resonant frequencies of the antenna can be tuned. This model describes an improvement to the cavity model of a rectangular coax-fed antenna whereby the dynamic permittivity accounts for the fringing fields of the patch. This model, valid for both electrically thin and thick substrates is well suited for computer-aided-design (CAD). The computations are compared with experimental data, showing good agreement