Compact Multi-Mode Quadrifilar Helical Antenna for GNSS-R Applications

In this paper, a compact circularly polarized (CP) multi-mode antenna for global navigation satellite system re- flectometry (GNSS-R) is presented. The design comprises two Quadrifilar Helical Antennas (QHAs), each fed with a ground coplanar waveguide (GCPW) and quarter wavelength power divider (QWPD) integrated feed. A hybrid staircase-shaped (SSR) QHA radial is proposed, and it is formed by serially arranging several vertical and diagonal elements. The electric field lines from the vertical elements converge constructively to radiate with the axis normal. Besides, the circular spatial offsets between the adjacent diagonal and vertical elements induce a 90 delay in the field radiated. This hybrid shape launches an unprecedented theory facilitating normal mode of operation (MOOp) in QHA and generates CP over broad elevations and azimuths (0<<80 and 0<<360). Besides, the port-to-port 90 spatial offset and the GCPW architecture yield high isolation (>20dB). Unlike conventional GNSS-R antennas, this compact (170.5 mm 132 mm) configuration operates in axial and normal mode, offers a broad beam coverage (237), minimizes pattern interference between the two QHAs upon gap-free stacking, and ensures high delay accuracy in the remote sensing data computed. Additionally, it supports proficient (efficiency>0.9) multi-constellation remote sensing. The design prototype was fabricated and measured, and the measurements agreed well with the simulations.