A Dual-polarized Planar Antenna Using Four Folded Dipoles and Its Array for Base Stations

A +/- 45 degrees dual-polarized base station antenna with a planar structure is proposed for 2G/3G bands. The +45 degrees antenna and the -45 degrees antenna share the same radiator, which is composed of four folded dipoles and four coplanar striplines. The coplanar striplines work as lambda/4 impedance transformers. Two Y-shaped feeding lines is designed to obtain a good impedance matching and a planar reflector is employed to achieve a stable radiation pattern. The antenna element has a wide impedance bandwidth of 27.8% with SWR < 1.5 (1.7-2.25 GH), and a stable radiation pattern and a high cross polarization discrimination (XPD) are also obtained across its operating frequency band. Also, an antenna array that consists of ten elements is developed for base station applications. The array is proposed for electrical downtilt and the downtilt angle is designed from 0 degrees to 8 degrees. The measured results show that a wide bandwidth of 30% (1.7-2.3 GHz), a great port-to-port isolation (>30 dB), a stable radiation pattern with 3-dB beamwidth 65 degrees +/- 5 degrees in the horizontal plane, a high XPD and a high front-to-back ratio were achieved.