Optimized absorbing boundary conditions for the analysis of planar circuits using the finite difference time domain method

It is shown that the description of absorbing boundary condition algorithms (ABCs) in terms of single incident plane waves does not provide sufficient information for choosing the best ABC for planar waveguide termination. A technique for optimizing the ABCs that results in a return loss from a wideband pulse less than -50 dB is demonstrated. This technique reduces the risk of loss of accuracy due to mode conversion at the boundary. The use of these optimized ABCs considerably improves analysis results for an important category of microstrip components. For boundaries transverse to the direction of propagation, it is shown that inaccuracy and late time instability can result if the boundary is placed in regions of high field strength