High-Gain Third-Order Filtering Patch Antenna Array With Two Radiation Nulls Using Cross-Radiation

A compact third-order filtering antenna array with high gain and two controllable radiation nulls is proposed. The antenna consists of one narrow patch in the center fed by the coaxial port and four wide patches placed around it. Four short-end stub-loaded resonators are capacitively coupled between the center patch and the outer patches, which makes the radiated E-fields of the center patch and the outer patches in-phase at the center frequency of the passband to realize the high gain and out-of-phase at the low and high stopbands to introduce a pair of radiation nulls. The working principle of the filtering antenna array can be explained by the coupled-resonator network. Finally, a filtering antenna array centered at 3.5 GHz with a fractional bandwidth of 4.26%, a high maximum gain of 12.2 dBi, high out-of-band selectivity, and wide stopband is designed, fabricated, and measured.