Design of Filtering Antenna for 5G FR2 Applications Using Characteristic Mode Analysis

In this letter, a design for filtering antenna based on the characteristic mode analysis is proposed, and the proposed antenna works in the 5G FR2 band (n257/n258). The design would adjust the working modes of the radiation structure to realize the filtering response by loading the filtering structures. Meanwhile, the characteristic modes of the feeding structure are analyzed. The feeding structure can introduce a radiation null. The coupling slot and the radiation structure realize two resonant modes to expand the bandwidth but also introduce high-frequency interference modes. The defective ground structure could suppress the interference mode and provide the third resonant mode to further extend bandwidth. To verify the design, the proposed antenna is fabricated and measured. The measured results show that the impedance bandwidth (
$S_{11}$
<−10 dB) is 19.3% with a peak gain of 8.58 dBi, and the efficiency can reach 87%. The antenna has multiple radiation nulls, and the stopband suppression level exceeds 28 dB compared with the maximum realized gain. Besides, no additional filtering circuit is introduced in this design.