A Low-Profile Circularly Polarized Spring-Shaped Quadrifilar Helical Antenna for Vehicle Satellite Navigation Systems

This work proposes a novel low-profile circularly polarized spring-shaped quadrifilar helical antenna (QHA) integrated on the car roof as a satellite navigation antenna to meet the practical needs of compact vehicles. The designed antenna consists of four helical radiating arms and a feed network. The antenna unit achieves low-profile characteristics mainly by folding and bending the radiating arms. Compared with the traditional QHA, the profile of the proposed antenna is reduced by 84.4%, with a height of only 13.4 mm (0.07λ). The designed feed network provides the QHA with equal amplitude and sequential 90° phase difference in the desired operating frequency band. The antenna prototype is realized by using 3D dielectric printing and post-metallization technology. The measured results show that the proposed QHA works in 1.558- 1.644 GHz, fully covering the B1 band of the BeiDou satellite navigation. Typically, at 1.575 GHz, the antenna's RHCP 3-dB beamwidth is 122°, with a 3-dB axial ratio (AR) beamwidth of 144°, providing a wide signal coverage range in the upper hemisphere. The proposed spring-shaped QHA exhibits good circularly polarized radiation performance and has the advantages of low cost and low profile, which is a promising candidate to ease the antenna integration into a compact satellite navigation platform of vehicles.