Bandwidth Behavior and Improvement of Miniature Cavity Antennas With Broadside Radiation Pattern Using a Metasurface

Several transmission line models of cavity antennas in an infinite ground plane are presented. Shorted square waveguides of side a, opening into a half space are considered as cavities. Predictions of bandwidth behavior from the models are compared to the theoretical bound on Q and predicted maximum bandwidth determined using the scattering approach. We demonstrate in which case the two approaches give the same bound and determine the minimum Q of such antennas to be 0.283 (a/λ0) when (a/λ0) <; 0.35. For several example aperture sizes, predicted maximum bandwidth versus cavity height is shown in the ground plane and compared with simulation results for patch antennas in cavities. Finally, the physical design of a new type of small cavity antennas capable of reaching the predicted maximum bandwidth is presented. Additionally, we show measurement results from a prototype of such an antenna which can be considered as a metasurface-inspired antenna.