Title: A PLANE WAVE EXPANSION SOLUTION FOR THE SCATTERING FROM A FREQUENCY-SELECTIVE SURFACE IN THE PRESENCE OF A DIELECTRIC

The scattering of a plane wave from a periodic broken-wire grid buried in a dielectric sheet is studied for a general angle of incidence and for arbitrary linear polarisation. The scattered field is expanded in a set of Floquet modes, and the modal coefficients are obtained through the current expansion for a reflecting antenna. The general formulation of the problm is applicable for grids in an infinite dielectric and when located at the boundary interface of two dielectrics. A moment method is used to determine the current on the grid elements and numerical results for the transmission characteristics of several different grid configurations are presented. In addition, the effect on the resonant frequency of parametric variations in the grid geometry is determined. Predicted ref its are compared with measured transmission characteristics and show excellent agreement. This memorandum is for advance informstion. It is not necesswily to be regawded as a final or official statemet by Procuremsnt Executive. Minist&quot