Open-ended waveguide radiation characteristics - full-wave simulation versus analytical solutions

Flush mounted aperture antennas are widely used and are often approximated by an aperture in an infinite conducting surface. The equivalent circuit parameters for the canonical problem of a rectangular waveguide radiating into a half-space (i.e., an infinite conducting flange) is equivalent to that for the parallel plate guide but using the guide wavelength. In 1951 Marcuvitz obtained an approximate solution by the variational method assuming a constant aperture field. Since then this canonical problem has received much attention with solutions obtained by various rigorous, approximate and numerical methods. Here we select some of the published results for comparison to numerical results obtained by the Method of Moments (MoM) using FEKO (www.feko.info) and the Finite Element Method (FEM) using Ansoft's HFSS (www.ansoft.com). The analytic results are based on the correlation matrix (CM), transverse operator (TO) and an integral equation method (KP). Although rigorous, these methods can be complicated and assume an infinite, zero-thickness conducting flange. To address realistic and possibly conformal antenna installations a numerical model is typically more accurate and more useful for antenna design. To this end FEKO is used to simulate a rectangular waveguide in a finite size flat plate for a single incident TE 10 mode. HFSS is used to simulate the waveguide with an infinite conducting flange. The results are used to estimate how large a waveguide flange is required to approximate the HFSS and previously published results for an infinite flange.