The passband of a convoluted slot array is switched in frequency by exchanging liquid substrates. In the example illustrated, liquid with ɛ_r ≃ 2.2 gives a 3 GHz frequency shift and a 16 dB change in the transmission coefficient at 17 GHz.

The analysis of the Fabry-Perot interferometer (FPI) is extended to cascaded surfaces with frequency dependent reflectivities, and provides a systematic procedure for the design of multilayer frequency selective structures (FSS). The FPI concept is also useful in diagnosing the origins of features in the transmission/frequency response curves. The approach eliminates much of the uncertainty in the initial design stages, where placing transmission and reflection bands at required frequency locations demands time and computing resources. The paper concentrates on double layer FSS and the application of the technique for design and diagnosis is illustrated by reference to the design of dichroic structures for microwave and submillimetre wavebands.

The development of a range of convoluted elements derived from linear and crossed dipoles is traced and their performance is examined experimentally and analytically in relation to their application to frequency-selective surfaces. These configurations give highly packed structures for use on curved surfaces or where maximum separation from the onset of grating responses is required. Two potential methods of analysis are a Floquet modal approach and a spectral iteration. Current distributions on an illustrative example are given. Calculated transmission responses of a convoluted dipole containing three cycles agree well with experiment.