Computation of resonant frequency of annular microstrip antenna loaded with multiple shorting posts

Shorting post loaded annular microstrip antenna is of considerable interest. Recent works have presented formulations for annular microstrip patch with a shorting post located at the centre of a circular disc, thereby converting the structure to an annular ring with a centre shot. A theoretical formulation for multiple post loading (up to ten posts) of an annular patch is presented. The posts are located away from the centre of the patch and are thin in diameter with respect to the diameter of the ring. The formulation accurately predicts resonant frequency. For an accurate formulation, the shorting posts have been considered as inductive impedances at the frequency of interest. It is shown that for a short loaded ring, TM₀₁ is the dominant mode. The simple tool presented can be suitably modified to incorporate switching diodes or varactor diodes.