Miniaturised frequency selective surface based on fractal arrays with square slots for enhanced bandwidth

Abstract

A novel approach is used to miniaturise the array size and broaden the bandwidth (BW) of a multilayer antenna-filter antenna- based frequency selective surface (FSS). Although such FSSs have broadly been investigated for higher frequency selectivity and less thickness, they still own high periodicity and lower BW. The proposed fractal FSS with centre square slots consists of three metallic layers, separated by two dielectric substrates and periodicity of the unit cell is sub-wavelength order (0.2 λ ₒ). Central square slots are added in the external Minkowski fractal patches to increase the capacitive effect whereas fractal slots are etched on the ground placed in the middle for enhanced coupling. It is demonstrated through simulations that proposed design can effectively minimise the element size and enhance the BW. Owing to minuscule array size and symmetric fractal geometry, the presented structure is insensitive to higher incidence angles (up to 30°) for both polarisations. A prototype of the proposed FSS is also fabricated and tested in a microwave anechoic chamber. An equivalent circuit model, full wave simulation and measurement results agree well and demonstrate stable response with 3 dB fractional BW approaching 87.4 and 92%, respectively, at a normal angle of incidence.