A Millimeter-Wave Antenna With Filtering Radiation Response Based on Absorptive Ring Feeding Circuit

This letter presents and analyzes an absorptive filtering antenna design operating in the 5G millimeter-wave (mm-wave) band. It consists of a two-port ring feeding circuit, a magneto-electric dipole (ME-dipole), and a square metal loop. The two-port ring circuit integrates bandstop-type transmission performance. Within the stopband of this two-port ring circuit, two controllable transmission zeros are deliberately generated to prevent the input signal from transmitting from one port to the other. As a result, the antenna operates as an effective radiator within this band. However, at the upper band frequencies, the input signal transmits from one port to the other, and thus the antenna does not work efficiently. To further improve the out-of-band radiation suppression level, a square metal loop around the ME-dipole arms is used. Based on such a simple structure, a bandpass-type filtering radiation response is realized. For demonstration, a filtering antenna array for 5G mm-wave applications (n257/n258/n261 bands: 24.25–29.5 GHz) is implemented and tested as an example. The measured average in-band gain is about 11.5 dBi, and a better than 16 dB out-of-band radiation rejection level is achieved.