Broadband Circularly Polarized Printed Crossed-Dipole Antenna and Its Arrays for Cellular Base Stations

Abstract

This study presents and investigates broadband circularly polarized (CP) printed crossed dipole antenna and its arrays. The proposed antenna comprises a pair of crossed fan-shaped dipoles, two kinds of parasitic elements, and a reflector with two vertical sidewalls. A three-quarter circular phase shifter connected to the fan-shaped arms of this antenna allows it to radiate CP waves owing to the excitation of the arms and the creation of sequential phases. The significant contribution of this study is the creation of electromagnetic coupling between crossed fan-shaped dipoles and parasitic elements to improve the purity of CP radiation and increase the axial ratio (AR) bandwidth. The proposed antenna has upgraded into 4-element and 8-element array models as cellular base station antennas for PCS/DCS/UMTS systems. Experiments indicate that the proposed CP antenna achieves an impedance bandwidth of 57% (1.47-2.65 GHz) for VSWR < 2, an AR bandwidth of 33% (1.65-2.3 GHz) for AR < 3 dB, and a gain of 7.8-8.7 dB. The implemented arrays of $1\times 4$ and $1\times 8$ arrangement achieve peak gains of 13.2 and 16.1 dB, respectively. The horizontal half-power beam widths (HPBWs), horizontal axial ratio beam widths (ARBWs), and front-to-back ratios (FBRs) for the antenna arrays are approximately 64°± 3°, > 90°, and > 25 dB, respectively.

Keywords

• Antenna array
• axial ratio
• base station
• circularly polarized
• crossed-dipole