High order resonances and scattering from FSS tripole arrays

A theoretical model is outlined where the scattered field is expanded in a set of plane waves called Floguet modes. An integral equation relating the induced current on the tripole elements to the periodic nature of the boundary conditions for the incident field is determined. Using an appropriate current expansion the method of moments is used along with Galerkin testing to obtain the modal coefficients in the expansion for the scattered field. Measured results are compared with predicted results for three different grids of tripoles. The transmission response of these grids are presented for copolarised signals in both parallel and perpendicular planes of incidence over the frequency range 7-20 GHz and for angles of incidence up to 60°. Both fundamental and higher order resonances are discussed