Investigation of annular ring microstrip antenna using conformal mapping

Annular ring microstrip antenna (ARMA) is investigated here using the conformal mapping technique. The annular ring shape is transformed into a rectangular one using conformal mapping. The wave equation is solved in the transformed domain to find the approximate solution of the eigenfunction and eigenvalue for different TMmnp modes. Resonant frequency, internal field patterns, input impedance and far-field radiation patterns are investigated. Internal field patterns are shown for the first few modes using the conformal mapping technique. Closed-form expressions are given to predict the far-zone electric field for different TMmnp modes. Our theoretical results are validated against the conventional spatial domain cavity model technique and measured data as found in the open literature. Two antennas are also fabricated in our laboratory for experimental validation. It is found that our theoretical results are in excellent agreement with 3D EM simulator and experimental data. In addition, our theory can predict the resonant frequency with an accuracy of 1.6% compared to the measured data. It is also found that our theory can predict the results much faster than commercially available 3D EM simulator (HFSS).