Polarisation properties of small printed spiral antennas with four resistively loaded arms

摘要

A small printed four-arm spiral antenna with lumped resistive loading is investigated to assess its suitability as a compact antenna element with pure circular polarisation. The results of numerical investigations based on a simplified thin-wire model are presented, which indicate XPD improvements of ≥ 14dB in comparison to conventional spirals of the same size. The corresponding gain reductions are ～1 - 3dB, which is at least equivalent to the performance of conventional cavity backed spirals. Furthermore, experimental results are discussed for a true microstrip spiral, which verify XPD improvements of 12 - 17dB and show that XPD figures of 30dB as well as a radiation pattern with acceptable symmetry can be obtained, even with simple nonoptimised feed networks. Areas for further improvements are identified and briefly discussed.