Computation of Green’S Tensor Integrals for Three-Dimensional Electromagnetic Problems Using Fast Hankel Transforms

A new method is presented that rapidly evaluates the many Green's tensor integrals encountered in three-dimensional electromagnetic modeling using an integral equation. Application of a fast Hankel transform (FHT) algorithm (Anderson 1982) is the basis for the new solution, where efficient and accurate computation of Hankel transforms are obtained by related and lagged convolutions (linear digital filtering). The FHT algorithm is briefly reviewed and compared to earlier convolution algorithms written by the author. The homogeneous and layered half-space cases for the Green's tensor integrals are presented in a form so that the FHT can be easily applied in practice. Computer timing runs comparing the FHT to conventional direct convolution methods are discussed, where the FHT's performance was about 6 times faster for a homogeneous half-space, and about 108 times faster for a five-layer half-space. Subsequent interpolation after the FHT is called is required to compute specific values of the tensor integrals at selected transform arguments; however, due to the relatively small lagged convolution interval used (same as the digital filter's), a simple and fast interpolation is sufficient (e.g. by cubic splines).