Compact Broadband Dual-Polarized Filtering Dipole Antenna With High Selectivity for Base-Station Applications

This paper presents a broadband dual-polarized filtering dipole antenna for base-station application, which has a compact size of 50 mm × 50 mm × 31.8 mm. The antenna consists of four parts: main radiator, feeding baluns, reflector, and two parasitic loops. Without using complex filtering circuits, the dual-polarized dipole antenna realizes satisfactory filtering performance and enhanced bandwidth by employing only two parasitic loops. Two specific radiation nulls are thus generated and individually controlled by the two parasitic loops. To further improve the upper stopband selectivity and bandwidth, a simple open-ended stub is added to the arms of the dipole. As a result, the bandwidth can be tuned from 7.4% to 47.6% and the realized gain is decreased dramatically from 8.6 dBi at 2.7 GHz (in-band) to -10 dBi at 2.9 GHz (out-of-band). For demonstration, a broadband dual-polarized dipole antenna is implemented. Measured results show that the proposed antenna has more than 34 dB port isolation over 48.7% (1.66-2.73 GHz) impendence bandwidth (VSWR <; 1.5). The measured in-band gain is about 8.15 dBi with stable 3 dB beamwidth 65.4°±2.4° in the horizontal plane, whereas the out-of-band radiation suppression is more than 17 dB.