Spatial filter with quasi-elliptical response

Spatial filters with quasi-elliptical responses are presented. Proposed designs are based on using the frequency-selective surface with at least two different apertures over the period. Such a surface provides the frequency response with a transmission zero. Just cutting additional aperture over the surface period makes possible such non-trivial feature. Two approaches to design a bandpass filter with quasi elliptical response are presented. In the first case a multiaperture surface is used as a high-quality resonant section, providing the response with the point of the total transmission and with two rejection resonances. In the second case, the grating of perforated strips, is used as a coupling element between half-lambda spatial resonators of an extracted-pole directly coupled filter.