FDTD analysis of an inclined microstrip patch antenna, considering field singularity at the edges

A rectangular microstrip patch antenna, inclined to the FDTD grid by 45/spl deg/, is accurately analysed using enhanced FDTD equations for diagonal metal edges. The enhanced equations, derived by considering the singular nature of electromagnetic fields at sharp metal edges, properly model the patch with less number of FDTD cells. The same inclined patch antenna is modelled using two existing techniques as well, namely staircase and split-cell models, for comparison with enhanced equations. The resonance frequencies and the frequency response of the patch are computed using these three techniques, and are compared with a very accurate reference, which is obtained by analysing a similar patch but kept parallel to a much finer grid. It is found that the enhanced equations give extremely accurate results consistently, without any noticeable computing overhead. For example, the accuracy of the first resonance frequency using the enhanced equations is 1.1%, and that using the staircase and split-cell models is 7.1% and 3.5%, respectively. The enhanced equations are very stable, and are time-stepped at the maximum Courant limit in all simulations without any problems.