Wideband Differentially Fed Dual-Polarized Antenna by Using Three-Strip Transmission Lines

A new method of designing a wideband differentially fed dual-polarized antenna by using three-strip transmission lines (TS-TLs) is presented. A wideband power divider composed of four TS-TLs is first proposed and illustrated by using its equivalent circuit. Based on the proposed power divider, a wideband differentially fed dual-polarized antenna with four in-band resonances is developed. To enhance the out-of-band selectivity, two radiation nulls with quasi-elliptic response are obtained by utilizing the specifically designed structures in the TS-TL-based power divider. The first radiation null at the lower out-of-band is produced by the resonance from the center strip of TS-TL and shorting coaxial cable. The second radiation null at the upper out-of-band is produced by the resonance from the slot formed by the dipole arm and the outer strip of TS-TL. Combining with the high second-order harmonic suppression owing to the differentially fed method, the presented differentially fed antenna is demonstrated that it not only has high in-band selectivity covering 1.67-2.91 GHz, but also has high out-of-band suppressions of 33.8 and 20.6 dB over the frequency bands of 0.6-1 GHz and 3.3-5 GHz. In addition, stable gain and beamwidth are achieved for base station applications.