A Compact Wideband Dual-Polarized Antenna With Enhanced Upper Out-of-Band Suppression

A compact wideband dual-polarized antenna with enhanced upper out-of-band suppression is presented in this paper. The proposed antenna is equivalent as two electric dipoles and two magnetic dipoles by using the crossed shunt loops. The incorporation of the electric and magnetic dipoles makes the antenna achieve wide impedance bandwidth and compact radiator size. In addition, four parasitic strips are inserted near the inner edge of the four loops to enhance the antenna upper out-of-band suppression at 3.5 GHz with improved impedance bandwidth. The antenna is fed by the crossed coaxial baluns with high isolation. A shorting sheet is introduced into the baluns to further enhance the upper out-of-band suppression and create another rejection at 4.9 GHz. To demonstrate the design method, the proposed antenna prototype was fabricated and measured. Measured results show that the proposed antenna has a wide impedance bandwidth of 1.625-3.05 GHz (61%) for S_11<-14 dB with the isolation better than 38.3 dB. The upper out-of-band suppression of the antenna is also largely enhanced with measured S_11>-2 dB from 3.35 GHz to 5.25 GHz. In addition, stable antenna gain and radiation patterns are achieved for base station applications.