Broadband Dual-Polarized Filtering Metasurface-Based Antennas Using Characteristic Mode Analysis for 5G Millimeter-Wave Applications

In this manuscript, two ±45° dual-polarized filtering metasurface-based antennas with high-suppression and wide stopband features for 5G millimeter-wave applications are, respectively, presented, which are both composed of a $2\times2$ uniformly distributed square metasurface structure and a cross slot to excite ±45° polarizations. Benefiting from the characteristic mode analysis (CMA), it can be found that the metasurface structure can provide an inherent upper radiation null to design filtering antennas. Further, by loading stubs and etching slots on the metasurface, several radiation nulls can be generated, which can realize one high-suppression filtering antenna with an out-of-band suppression level of about 30 dB. Next, by rotating the metasurface structure and stubs at 45°, the positions between the metasurface and feeding slot are changed; thus, lesser CMA modes radiating at broadside direction are excited in the upper stopband, resulting in a wide stopband feature, and the stop suppression range is about $2.15f_{0}$ (where $f_{0}$ is the center frequency). Finally, for demonstration, these proposed antennas with simple structures and high integration were fabricated by using the low-temperature co-fired ceramic (LTCC) process. The measured results show that these prototypes exhibit good filtering performances in the 5G millimeter-wave frequency band.

I. Introduction

Millimeter-wave communication is an essential technology for 5G (the fifth-generation mobile communications) applications due to its advantages of high speed, low latency, and abundant spectrum resources. As 5G millimeter-wave communication technology develops further, higher demands are put forward for the communication system; however, the traditional discrete designs of filters and antennas, which are crucial components in the front-end of communication systems, are no longer sufficient to meet the requirements of miniaturization and low power consumption. High-Q filters are too bulky to integrate with chips, posing, furthermore, a challenge to the development of communication systems. To address these issues, a passive device called filtering antenna has been introduced in [1], which combines filtering and radiation functions to reduce size effectively without increasing extra circuits. This integrated design can reduce the insertion loss and improve efficiency, providing a solution for improving 5G millimeter-wave systems.