S-parameter extraction of 3-D microwave structures by using 3D-FDFD method in conjunction with asymptotic waveform evaluation technique

The 3-D FDFD (frequency domain finite difference) has been a very useful tool for the simulation of 3-D microwave structures such as multilayered patch antennas. In the 3-D FDFD, the Maxwell equations in the frequency domain is discretized in space and the so-called absorbing boundary conditions (ABCs) is employed to truncate an infinite problem space to a finite computation domain, which becomes a matrix equation problem. The generation and solution procedure of the matrix are the two major factors affecting the computational efficiency. We extend the asymptotic waveform evaluation (AWE) to the calculation of S-parameters using FDFD method. In the AWE technique, the electric field at the input and output port is expanded in the Taylor´s series around some frequency point and the coefficients of Taylor´s series are evaluated by the FDFD. Using the rational function, the electric field distribution at the input and output port can be obtained at any frequency within the desired bandwidth and the S-parameters can also be obtained. Numerical results for the waveguide structures are given and a good agreement between the AWE and the exact solution is observed.