Circuit models explaining bandwidth behavior of small circular cavity backed patch antennas

The objective of this work is to determine the orders of magnitude of the bandwidth available from a patch antenna enclosed in a small finite circular cavity. Numerical investigations were performed using commercial software where the antenna was optimized to resonate at 2.3GHz. We considered cavities with aperture diameters of 32mm (0.25 λ₀), 40mm (0.3 λ₀) and 50mm (0.38λ₀) and substrate permittivity of 3.66, 6.15 and 10.2 inside the cavity volume. Results for bandwidth behavior are shown in dependence on cavity height up to the maximum height where matching the patch antenna with a probe feed was still possible. Bandwidth performance is also analyzed analytically using simple transmission line models that can describe the antenna behavior in a qualitative manner and explain several unexpected results shown in the paper. Numerical results for patch antennas are also compared to analytical predictions for a simple cavity antenna of the same size without a patch, assumed to be excited only by the fundamental waveguide mode.