An End-Fire Circularly Polarized Antenna with Small Clearance for Mobile Terminal Devices

This paper presents a planar end-fire circularly polarized antenna with a simple configuration and minimal ground clearance for mobile terminals. It was developed based on a half-wavelength folded TE<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5,0</inf> mode rectangular waveguide cavity functioning as a magnetic dipole (MD), which provides vertical polarization. By etching a Γ-shaped open-ended slot in the top metallic surface of the waveguide, another horizontally polarized electrical dipole (ED) mode is realized. The required 90° phase difference and equal amplitude for the pair of orthogonal polarization modes to achieve CP radiation in the end-fire direction can be attained by fine-tuning the slot dimension parameters. Simulated results indicate that the proposed antenna achieves an overlapped bandwidth <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\vert \mathrm{S}_{11}\vert &lt; -10$</tex> and AR < 3 dB) of 1.2%. In the end-fire direction, it can produce a CP beam with a peak gain of 2.4 within 85°. Furthermore, to broaden the antenna's beamwidth, a two-element array arranged in a back-to-back configuration is proposed. Simulated results demonstrate that this method can significantly enhance the beamwidth to 130 °.