Monopole antenna with a rectangular ring on the circular ground plane

A simple structure of monopole antenna, providing a bidirectional pattern, is proposed. The antenna consists of a monopole antenna surrounded by a rectangular ring. They are mounted on a circular ground plane. The characteristics of the antenna are investigated theoretically in the range 4.8-5.6 GHz, and verified by experiment. Measurements have shown that the antenna demonstrated a bidirectional pattern with a moderate antenna gain of around 4.5 dB and it is well matched.