Fast modal ABC´s in the hybrid PEE-FDTD analysis of waveguide discontinuities

The authors discuss the application of two types of fast modal absorbing boundary conditions (ABC´s) to the analysis of waveguide discontinuities by means of the hybrid partial eigen-function expansion finite-difference time-domain (PEE-FDTD) method. For low-order modes, ARX digital filters are used while higher order modes are terminated with simplified ABC´s based on the evanescent nature of modes below cutoff. Numerical tests show that this approach gives a very good absorption of modes while allowing one to achieve significant acceleration of numerical computation compared to classical FDTD scheme.