Design of a Filtering Antenna With Hybrid Feed Structure for 5G Communications

This article investigates a filtering patch antenna with improved cross-polarization for sub-6-GHz applications. A novel filtering feed network is implemented to excite the patch radiator and provides three radiation nulls. The feeding network mainly consists of two vertically coupled microstrip line arms printed on a PCB. The upper arm forms a hybrid feed mode for the patch radiator, which combines proximity-coupled and probe-fed methods to achieve a passband and two radiation nulls near it. In addition, one additional null is introduced by the coupling scheme of the two arms to achieve a better filtering response. Meanwhile, two shorted stubs are embedded and coupled with the lower arms to improve both the out-of-band and cross-polarization suppression. As a result, a filtering patch antenna operating from 3.3 to 3.77 GHz with a low cross-polarization level of −25 dB and an out-of-band gain suppression of −18 dB is obtained. The filtering antenna is fabricated and measured to validate the design. The measured results reveal that the antenna reaches a good filtering character and low level of cross-polarization, making it suitable for 5G n78 operations.