Circularly Polarized Mode-3 Quadrifilar Helical Antenna With Wide-Beam-Coverage Radiation

Vehicle-mounted antenna for satellite communications needs to simultaneously have a compact structure, high front-to-back ratio (FBR), wide beam coverage, good <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ϕ</i>-directional omnidirectionality, and an AR bandwidth wider than 10%, which existing circularly polarized (CP) conical beam antennas cannot achieve. A CP mode-3 quadrifilar helical antenna (QHA) with a small pitch is presented in this work to satisfy these requirements. The proposed compact mode-3 QHA can achieve two orthogonal far-field electric field components with a phase difference of nearly 90° and equal amplitude at a wide range of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ϕ</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> through its traveling-mode <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ϕ</i>-directional current component alone. A parasitic patch serving as the ground plane for the microstrip lines is placed above the helical arms to further improve <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub>, axial ratio (AR) and FBR. A parasitic loop with open-circuited branches is designed below the helices to further improve the omnidirectionality. The proposed QHA has a stable performance with or without a vehicle environment. To validate the design, a prototype has been fabricated and measured, demonstrating good radiation performance.