Wide-band hybrid computational electromagnetic technique using an impedance/admittance interpolation method

A hybrid technique linking the frequency-domain method of moments (MoM) and the finite difference time domain (FDTD) method provides a powerful and flexible approach to the numerical solution of a complex antenna structure in the presence of a large lossy dielectric body, especially if it is inhomogeneous. If broadband analysis is required, such as the transient response for a sub-surface radar, this can be accurately modelled by iterating the field propagation over the two different domains. To do this it is necessary to compute the fields on an equivalence-principle surface (the surface that couples the two domains), over the entire bandwidth. In this paper, the fields are computed using the method of interpolation of impedance/admittance matrices on the antenna side, using MoM. This saves execution time and memory requirements for the MoM. Basically, the inverse discrete Fourier transform (IDFT) is performed on the equivalence-principle surface within the FDTD domain and, on the other hand, the discrete Fourier transform (DFT) is used to account for the back-scattered fields for the MoM domain. The number of frequency samples required to predict the coupling fields between the two domains over the entire bandwidth is investigated and discussed. The positions of these samples over the selected bandwidth are also studied in relation to their effect on recovery of the time-domain fields for different resonant structures. Several examples are presented and the results are compared with available data.