Attention is focused on analysis of waveguide circuits using the ADI-FDTD+GRT method to reduce the computational resources required.First

the conventional Geometry Rearrangement Technique (GRT) is modified for the soft source excitation and whole S-parameters can be obtained by locating the source plane and the reference planes correctly.Not only the dominant boundary reflection can be cancelled but also the computational domain can be reduced by the modified GRT.And then the Alternating-Direction Implicit Finite-Difference Time-Domain (ADI-FDTD) method is combined with the modified GRT.By the ADI-FDTD+GRT method the computational time and domain are saved

respectively.In order to demonstrate the computational accuracy and efficiency of this method

a waveguide with discontinuous structure is simulated as an example.The numerical results of this method are compared with those obtained by the conventional FDTD method and the HFSS.In addition the numerical results and the computational requirements of the different ADI-FDTD+GRT cases are compared with those of the conventional ADI-FDTD method.It is found that this method is accurate and efficient.