An Aperture-coupled Patch Antenna Design for Improved Impedance Bandwidth

The Method of Moments, implemented in 2.5-D with the multilayer Green’s Function, or implemented as a fully 3-D solution of Maxwell’s equations, is a popular method for microwave antenna simulations. Commercial software was used to simulate two different designs for a single aperture-coupled patch antenna element. The simulation results are compared with experimental data measured for antenna prototypes having substrate and ground plane dimensions 4-in x 4-in. For C-Band applications (4.4 – 5 GHz) a conventional patch antenna solution, with stub-terminated microstrip feed and slotted ground plane, would not cover the entire band. A different design, incorporating thicker substrate layers and a bottom ground plane for unidirectional radiation, was modeled in 2.5-D with encouraging results. The design had improved bandwidth and was fabricated even though the simulations results were known to be approximate. The concern for the microstrip feed structure is the frequency variation of the propagation velocity and the presence of higher order waveguide modes that are not incorporated in the simulation but serve to limit the measured bandwidth. We compare the calculated and measured antenna performance and show that specialized software is often sufficient for the design of conventional aperture-coupled patch antennas but can be misleading for thick substrates.