A Compact Quasi-Magnetic-Electric Circularly Polarized Antenna With Reconfigurable Patterns

A novel compact quasi-magnetic-electric circularly polarized (CP) antenna with reconfigurable patterns is proposed. The antenna, featuring a compact structure and a simple feeding mechanism, can generate four endfire CP radiation beams covering the entire azimuth plane. The antenna is composed of four quasi-magnetic-electric elements arranged in rotational symmetry. Each element consists of two layers of staggered trapezoidal shorted metals with a compact size of 0.51λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.16λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.05λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> denotes the free-space wavelength at 900 MHz) and is designed to provide an endfire CP beam with a single feed. By integrating four such elements and switching the excited elements through the feeding ports, the antenna can obtain four endfire CP radiation patterns in different directions. The prototype antenna has a compact size of 0.54λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.54λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.05λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>. The operational bandwidth of the fabricated antenna, constrained by |<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>| < −10 dB and the 3 dB axial ratio, spans from 867 MHz to 928 MHz. The proposed CP pattern-reconfigurable antenna can be a promising candidate for various applications, including radio frequency identification, Internet-of-Things, and indoor localization.