Analysis of thin multioctave cavity-backed slot spiral antennas

Thin cavity-backed Archimedean slot spirals are analysed through an efficie nt implementation of the finite element method. Through numerical analysis, fundamental differences between the free-space and cavity-backed configura tions are identified. The bandwidth limitation imposed by the presence of t he cavity is remedied by terminating the spiral slot with tapered resistive loading and employing larger apertures. Design improvements are presented based on the interpretation of the numerical simulations. It is shown that a 0.8 cm (0.33 in) thick and 24 cm (9 in) wide antenna can provide circular polarisation over a nearly 4:1 bandwidth.