Equivalent-circuit models for frequency-selective surfaces at oblique angles of incidence

The equivalent-circuit-modelling technique is useful for designing printed frequency-selective surfaces. A correction term is derived which enables transmission responses to be modelled at oblique angles of incidence. Models derived for arrays of gridded-square and double-square elements are compared with experimental results for plane waves at normal incidence and at oblique angles for TE- and TM-incidence. Good agreement is obtained for angles of incidence up to 45° in the principle planes. The importance of using the immittance correction terms in the models is also discussed.