Vector Hankel transform analysis of annular-ring microstrip antenna

A rigorous analysis of the resonant frequency characteristics of an annular-ring conductor printed on a dielectric substrate backed by a ground plane is presented. The problem is cast into a set of vector dual integral equations by using vector Hankel transform (VHT). Galerkin\´s method is then applied to compute the resonant frequencies of both transverse magnetic modes (TM11and TM12) of the microstrip antenna. The real part of the resonant frequency shift of the TM11mode increases with increasing dielectric thickness in contrast to the TM12mode. While the TM11mode has a high , it is a poor radiating mode; the TM12mode is more suitable for antenna applications. For a probe excitation the input impedance is obtained using single mode approximation for both the TM11and TM12modes. It is shown that the TM12mode of the annular ring has a greater bandwidth than the TM11mode.