Balun-Fed Dual-Polarized Broadband Filtering Antenna Without Extra Filtering Structure

A dual-polarized filtering antenna without using extra parasitic element or filtering circuit is proposed. The proposed antenna consists of two pairs of dipole arms and baluns. The balun feeding scheme is used to form two half-wavelength resonators, which introduce two radiation nulls in the upper stopband. Meanwhile, in the lower stopband, another radiation null is generated by the radiation cancellation between the dipoles and the baluns. As a result, a bandpass filtering response is realized owing to these three radiation nulls. For demonstration, a prototype is fabricated and measured. The prototype has an impedance bandwidth of 50% (return loss >15 dB within the band 1.65-2.75 GHz). The average measured gain is 8.1 dBi. Within the lower stopband of 0-1.25 GHz, the out-of-band suppression level is more than 30 dB. Furthermore, the suppression level is over 16 dB in the upper stopband of 3.3-5 GHz. Such features make the proposed antenna suitable for multiband array applications to reduce the mutual coupling between elements operating at adjacent frequencies.