Finite planar- and curved-ring-element frequency-selective surfaces

An element-by-element approach to the modelling of arrays of finite size enables the elements to be located on arbitrary lattices, including those curved in more than one plane. An analysis for dual-polarised ring-patch elements is given. Planar and parabolic surfaces are used as examples, with the rings on circular and triangular lattices. They are illuminated by plane waves. The currents induced across the arrays are very dependent on element location as well as on frequency. The transmission performance of these curved frequency-selective surfaces is also discussed, including the effect on the current induced in an element located inside a paraboloidal dichroic enclosure.