Plane-wave illumination of concentric-ring frequency-selective surfaces

In the paper we present the results of a modal analysis of the current distribution around the circumference of thin concentric rings arranged on both square and equilateral triangular lattices. The particular case of plane-wave illumination at 45° incidence is considered owing to its relevance to oblique-incidence diplexer systems. Measured and predicted transmission curves, together with computer curves illustrating the frequency dependence of various current-mode amplitudes, are plotted for selected concentric-ring structures, each with the same mean radius for the outer ring, but with different inner-ring radii. The results relate individual current modes to features in the observed transmission curves. They confirm that the copolar transmission and lower reflection bands can be modelled with only one current mode in each ring. Crosspolar effects are discussed for incidence on the square lattice in the planes ¿ = 0, 45° and 90°, where they are shown to be small for pure TE and TM.