A multi-frequency microstrip-fed shorted square ring slot line antenna

Abstract

A single-feed three-frequency shorted square ring slot antenna is described. The feed is an open-circuited microstrip line and is electromagnetically coupled to the ring slot antenna at two locations. The radiation pattern of all resonant frequencies is broadside and bidirectional. Impedance bandwidths of 3 to 9 percent and antenna gains on the order of 5 dB are achieved.