Current distribution across curved ring element FSS

Planar frequency selective surfaces (FSS) are usually modelled using the Floquet modal technique or the semi-empirical equivalent circuit method. Arbitrarily curved or finite surfaces present greater problems because it becomes necessary to perform computations for groups of elements or for individual elements in the array. The currents induced in individual elements on finite plane and curved lattices are computed in this paper, to study the influence of curvature on the distribution of current in the elements, and hence the amount of curvature that might be tolerated before the locally plane assumption breaks down. In constructing a doubly curved lattice, symmetry suggests placing an element at the apex and surrounding it with successive circles of additional elements. The elements are free standing single rings, which are commonly used in FSS This element-by-element approach to the analysis of FSS enables the properties of arrays on arbitrary lattices to be studied, including 3-dimensional ones. In this paper, the arrays are doubly curved. A requirement is an expression for the scattering by a single element, as is provided for these dual polarised rings. The rings do not have to be identical: finite arrays of concentric ring elements could be simulated using the same method.