Compact Cavity-Backed Spiral Antennas with Enhanced Axial Ratio and Gain at Low Frequencies

A simple method to improve the gain and axial ratio of cavity-backed spiral antennas at low frequencies is presented. The inclusion of appropriate non-metallic materials in the upper cavity walls allows the design of compact antennas without a significant performance degradation at low frequencies. A two-arm Archimedean spiral antenna is designed and simulated in order to validate this method. The antenna can operate in a wide frequency band from 2 to 18 GHz. The results obtained show a considerable gain and axial ratio improvement at 2 GHz.