Lens loading approach for improving ultra-wideband performance of spiral antennas

A hemispherical dielectric lens is utilised to reduce the amplitude distortion in ultra-wideband spiral antenna communication links. It is shown that a small lens action achieves a nearly constant-aperture frequency response needed to flatten the system's transfer function when the receiving antenna has a nearly constant gain. A system fidelity factor improvement of over 26% is achieved. In addition, the lens is used to reduce the negative impact of electrical effects of shallow-cavity backing on gain and efficiency while preserving high-quality radiation patterns. Detailed computational and experimental analysis demonstrate a lens-loaded spiral antenna with voltage standing wave ratio (VSWR) <1.6, axial ratio <2 dB over multi-octave bandwidth, significant gain and efficiency improvements and fidelity factor of over 90%.