Annular-Ring and Circular-Disc Microstrip Antennas with & without Air Gaps

A systematic study is first presented on the impedance bandwidth characteristics of the first few modes of the annular ring and the circular disc microstrip antennas. It is then established, both experimentally & theoretically, that the resonant frequencies can be tuned and the bandwidths widened by introducing an adjustable air gap between the substrate and the ground plane.