Patent ID: 6218978
Filing Date: 2001-04-17
Classification: H01Q

Abstract:
A frequency selective surface, comprising:at least one sheet-like frequency selective layer made up of an array of non-electrically conductively spaced apart electrically conductive elements,at least one electrically conductive sheet-like frequency selective layer having an array of spaced apart non-conductive apertures therethrough overlaying said element layer with the apertures overlaying the elements, anda sheet of dielectric material separating said at least one element layer and said at least one aperture layer, wherein:elements in the element layer are complementary in plan view shape to the apertures in the aperture layer,said elements are aligned in the plane of the element layer in a direction at 90.degree. to the direction of alignment of the apertures in the plane of the aperture layer so as to provide a Babinet Complement between the at least one element layer and the at least one aperture layer,the element layer and the aperture layer are substantially parallel to one another,the element array and the aperture array have the same periodicity, andthickness of the sheet of dielectric material, and thereby a separation distance between the at least one element layer and at least one aperture layer, is chosen to provide a value for a ratio of free space wavelength at passband frequency to the periodicity of the element and aperture arrays in excess of the value obtainable for a corresponding conventional single layer frequency selective surface, to improve the frequency separation between the passband resonant frequency and grating lobe cut-on frequency of the frequency selective surface.