Focusing effects of quasiperiodically distributed frequency selective structures

A spectral domain representation is derived as a Fourier summation over waves in discrete specular directions (Floquet modes). The Floquet representation for periodic dipole grids and the extension to more complex structures (for example, square loops) are given. Suppositions entering the numerical calculations are explained together with a comparison of a dipole and square loop grid concerning the specifications of the transfer function. Based on Floquet theory an extension is given to describe finite apertures with spatially varying local electrical properties as given by the amplitude and phase of the reflection coefficient. The approached based on a window technique in the space domain, introducing a local current distribution. An example of application is given for a dielectrically loaded planar surface showing quadratic phase distribution and acting as a focusing reflector. Results of experimental investigations are presented for planar scans parallel to the aperture with (optional) broadband frequency discrete sampling in the range from 6.5 to 15.5 GHz followed by a time domain filtering procedure