An FDTD/MoM hybrid technique for modeling complex antennas in the presenceof heterogeneous grounds

Calculating the current distribution and radiation patterns for ground-pene trating radar antennas is a challenging problem because of the complex inte raction between the antenna, the ground, and any buried scatterer. Typicall y, numerical techniques that are well suited for modeling the antennas them selves are not well suited for modeling the heterogeneous grounds, and visa versa, For example the finite-difference time-domain (FDTD) technique is w ell suited for modeling fields in heterogeneous media, whereas the method o f moments (MoM) is well suited for modeling complex antennas in free space. This paper describes a hybrid technique, based upon the equivalence princi ple, for calculating an antenna's current distribution radiation pattern wh en the antenna is located near an air-ground interface. The original problem is decomposed into two coupled equivalent problems: on e for the antenna geometry and the other for the ground geometry, with fiel d information passing between them via a rapidly converging iterative proce dure, The fields in each region may be modeled using numerical techniques b est suited to them, Results for several test cases are presented, using FDT D to model the ground problem and MoM for the antenna problem, that demonst rate the accuracy of this hybrid technique.