A Compact Single-Layer Pattern-Reconfigurable Antenna for 5G Vehicular Communication

This paper presents a single-layer pattern reconfigurable antenna for fifth-generation (5G) vehicular communications. The antenna consists of an active dipole, which is directly fed through a feeding port, and three passive dipoles excited by the near fields of the active dipole. Pattern reconfiguration is achieved using three p-i-n diodes placed at the center gaps of the passive dipoles, enabling three unidirectional beam modes: two endfire beams in opposite directions and one broadside beam. The antenna effectively suppresses backward radiation, ensuring a unidirectional radiation pattern in each mode. It has a thin thickness of 0.7 mm and achieves a front-to-back ratio (FTBR) of 22.8 dB and 24.8 dB at 28 GHz for the endfire and broadside modes, respectively. Additionally, it attains a realized gain of 6.36 dBi and 5.38 dBi at 28 GHz for the endfire and broadside modes, respectively. The proposed antenna operates in the bandwidth of 26.3 GHz to 29 GHz with an FTBR above 10 dB and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{S}_{11}$</tex> less than −10 dB. Additionally, the antenna achieves a radiation efficiency of 95.7% and 94.2% for the endfire and broadside radiation patterns.