Close Band Spacing Pentaband Frequency Selective Surfaces Based on Concentric Ring Slots

This paper presents a polarization insensitive frequency selective surface (FSS) based on concentric ring slots with five closely spaced passbands. The proposed FSS unit cell contains coupled supplementary innermost slot. close band response within the first transmission bands is achieved by influence of modified geometry obtained inclusion sixth added slot causes appearance stopband, due to conductive between fifth and apertures, passband produced inherently aperture. effect additional stopband in has been investigated paper. Full-wave simulations reveal that proper sizes effectively enables pentaband FSS. To validate approach, 729-element penta-bandpass prototype operating at millimeter-wave frequencies designed, fabricated, tested. Experimental results free-space measurement setup indicate resonances $f_{1} =26.7$ , $f_{2} =29.8$ $f_{3} =33.6$ $f_{4} =38.1$ $f_{5} =44.2$ GHz, resonant ratios / f_{1} =1.12$ f_{2} =1.13$ f_{3} f_{4} =1.16$ . demonstrates an extremely low ratio highest lowest ( =1.66$ ) for penta-band operation. good performance oblique angular incidence elevation angles up 45°.