Novel Filtering Method of Metasurface Antennas Based on 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 2×2 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. Furtherly, 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 about 30dB. Next, by rotating the metasurface structure and stubs with 45°, the positions between the metasurface and feeding slot are changed, thus less 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 2.15f0 (where f0 is the center frequency). Finally, for the fabrication of Antenna B, the ground is enlarged and the defect ground structure (DGS) is adopted to weaken the influence by the large-full ground.