Compact Dual-Band Dual-Port Nested Coaxial Quadrifilar Helix Antenna With High Efficiency for Small-Scale Autonomous Surface Vehicles

This letter presents a compact, high-efficiency, dual-band, dual-port nested coaxial quadrifilar helix antenna (QHA) for navigation and SATCOM in small-scale autonomous surface vehicles (ASVs). The antenna is formed by two coaxially nested QHA radiators, resulting in a compact size, and each band corresponds to an independent port, avoiding additional diplexers. Unlike previous designs, an analysis method based on generalized multimode (GMM) is developed to evaluate radiators' reflection and inter-radiator coupling, effectively overcoming the coupling analysis complexity of single-end, improving radiation efficiency, and addressing the low-gain issue in conventional nested coaxial QHAs. A prototype operating at 1.575 GHz and 1.995&2.185 GHz achieves more than 17 dB port isolation without additional filters, peak gains of 5.5 and 5.4 dBic, and radiation efficiencies of 81.5% and 80.5%, in close agreement with simulations. More importantly, the proposed design and its analysis method are readily extendable to multi-band, multi-port nested coaxial QHAs, providing a compact, high-performance antenna solution for ASVs and other small-scale autonomous platforms.