Theory and Experiment of UWB Archimedean Conformal Spiral Antennas

A conformal UWB Archimedean spiral antenna on a dielectric hemisphere is theoretically and experimentally investigated. The analysis method, design, and optimization of this type of spherical antennas is performed using an efficient spatial domain method of moments in conjunction with triangular basis functions and asymptotic Green's functions. A special conformal mapping is used to enhance the impedance bandwidth and axial ratio (AR) bandwidth for a circularly polarized spherical spiral antenna. Emphasis is given to the efficient asymptotic approach in spherical multilayered media. To validate the theory, a UWB leaky-wave conformal spiral antenna was designed, manufactured, and tested. The measured results indicate a pretty wideband behavior for this antenna starting from 1.7 to 6 GHz (1.8 octaves) in its input impedance responses. The circular polarization is maintained over 1.26 octave with less than 3 dB AR.