Bandwidth behavior of miniature square cavity microstrip antennas

Integrating an antenna onto a specific platform of small size often requires its placement in a metallic cavity. The main consequence is the reduction of the antenna bandwidth. The objective of our study is to investigate the maximum possible bandwidth at a fixed frequency of 2.3 GHz for a patch antenna in a small square cavity. For this study, square cavities of sizes 32mm (0.245λ₀), 40mm (0.3λ₀) and 48mm (0.37λ₀) are considered. We show results for three permittivity values of antenna substrate, namely 3.66, 6.15 and 10.2 and for various values of the cavity height up to a maximum possible height where matching is still possible. Unexpected dependence of bandwidth on permittivity is observed when cavity height is approaching the guided wavelength of the dominant TE mode in the cavity. Numerical results for patch antennas are compared to analytical predictions using a waveguide model for a simple cavity antenna of the same size without a patch and excited only by the TE mode.