Application of enhanced FD-TD equations to analyse coupling between inclined microstrip patch antennas

Mutual coupling between pairs of rectangular microstrip patch antenna elements that are inclined to the FD-TD grid by 45 degrees is analysed using enhanced FD-TD equations for diagonal metal edges. These enhanced equations, derived by considering the field singularity at a sharp metal edge, model the coupling effect between two patch antennas very efficiently and accurately. Mutual coupling is analysed using two established techniques as well, namely the staircase and the split-cell, for comparison with the enhanced-equation technique. It is found that the enhanced-equation technique gives extremely accurate results consistently, without any noticeable computing overhead. For example, the accuracy of the first peak of the frequency response in one case is 0.7% from the enhanced-equations technique whereas the same from the staircase and split-cell techniques is 9.8% and 4.4%, respectively. The enhanced equations were found to be very stable, and were time-stepped at the maximum limit in all simulations without any problems.