Higher Order Multipole Model of a Thin-Wire Helix

We investigate the field scattered from thin-wire helices by means of vector spherical harmonics rendering the fields of generated multipoles of arbitrary order. The excitation is varied in order to yield the characteristic T-matrix of a single helix column by column. The convergence with respect to the number and kind of required multipoles is checked by means of a simple test case. Further, we consider the mutual interaction of two helices. It is shown to be equivalent to an averaging process in terms of the number of required multipoles, which is thus limited. The helix model is then utilized to investigate reflection and transmission properties of a specific periodic arrangement which allows a comparison to a finite element based commercial software tool.