Analysis of rectangular microstrip antenna using theory of characteristic modes

In this paper, the rectangular microstrip antenna is analyzed by using the theory of characteristic modes (TCM). Characteristic modes of microstrip antennas with different shapes of ground are presented to provide physical understanding of the radiating behavior. The microstrip antennas operated at different modes are verified by both HFSS simulated and measured results. Resonance frequency, near field, eigencurrent, radiation pattern are analyzed and compared. The results show that some modes which similar to that obtained by cavity model could be carried out. The error of resonance frequencies of these modes predicted by TCM and cavity model is less than 2%. It is demonstrated that they are conventional TM modes.