A Novel Differentially-Fed Dual-Polarized Filtering Antenna for Base Station

The theory, design and experiments of a wideband dual-polarized filtering antenna are presented. A novel technique, which combines the use of open loops, parasitic loop, and extended ground plane, is proposed to realize two upper band radiation nulls and a lower band radiation null. Thanks to these radiation nulls, the proposed antenna obtains a sharp cut-off at the edges of the operating band. To achieve wideband performance, another novel technique of exciting multiple resonant modes of the crossed dipoles and parasitic loop is proposed. The measured results demonstrate that this antenna achieves a wide impedance bandwidth from 1.7 to 3.01 GHz (56%), high isolation of 38dB, low cross-polarization within the working frequency band and also filtering performance. At 3.17 GHz, the gain of the antenna will drop rapidly to -18.1 dBi, which is 26.4 dB lower than the average in-band gain. These advantages make the proposed antenna a good candidate for base station applications.