A Compact, Broadband, Monopole-Like Endfire Antenna With Reconfigurable Patterns for 5G Applications

This communication presents a novel compact, broadband, monopole-like endfire antenna with reconfigurable radiation patterns for 5G applications. Based on the mirror principle, a half-size monopole-like endfire structure with a wideband response is firstly proposed and analyzed. By switching the ON/OFF states of p-i-n diodes embedded in the passive stub lines, the monopole-like endfire structure achieves omnidirectional and endfire beam switching. Since the structure has a stable and broadband frequency response, a novel flexible pattern diversity antenna with omnidirectional coverage and directional scanned radiation is easily implemented by loading multiple stub lines. To validate the working principle, a nine-mode pattern reconfigurable antenna with a compact size of
$0.31\,\,\lambda _{0}\,\,\times \,\,0.31\,\,\lambda _{0}\,\,\times \,\,0.19\,\,\lambda _{0}$
(
$\lambda _{0}$
is the free space wavelength at 3.75 GHz, radiator only) is designed and fabricated. The measured overlapped −10 dB impedance bandwidth for the nine modes is from 3.30 to 4.20 GHz (>24.0%), which well covers the 5G N77/N78 band. Besides, their measured gain is greater than 4.0/5.30 dBi. The proposed antenna has the merits of a compact size, simple design, wideband, good radiation performance, and flexible multibeam switching capacity. It is a good candidate for 5G new radio and other sub-6 GHz applications.