Convoluted array elements and reduced size unit cells for frequency-selective surfaces

The transmission response of a typical array of conducting elements has a main reflection resonance at a wavelength lambda 1, with further s at shorter wavelengths. The authors have attempted to reduce the unit cell dimension p as much as possible for a given reflection wavelength lambda 1, thereby increasing its separation from grating responses. The ratio lambda 1/p has been used as a figure of merit. An array of linear dipoles on a square lattice of side p is a standard of comparison, a typical case giving a figure of merit of 1.6 AA Jerusalem cross array gives a value of about 4.5. By convoluting the conductors of a square loop element, or by using, as the array elements, the low order generations of space filling curves, such as that described by Hilbert, values of lambda 1/p in the range 7-12 have been obtained. The unit cell areas are lower than that of the dipole standard by factors averaging about 40.