Unidirectional spiral antenna with improved gain and WoW

Spiral antennas are widely used for applications that require broadband performance with a high quality circular polarization and consistent radiation pattern. We investigate several cavity backing configurations that enhance the radiation from the active regions over a 9:1 band. Specifically, co- and cross-wound spirals are proposed as a cavity backing. It is shown that the spiral with a co-wound backing has a more than 1 dB increase in nominal gain and a 3 dB wobble-of-the-wave (WoW) bandwidth that is over 25% wider than a traditional absorber backed antenna. Besides improved pattern symmetry and gain, the proposed configurations contribute to a significant reduction in cavity depth and the overall weight of the entire antenna, issues important for space borne applications.