Characteristic mode inspired broadband circularly polarized metasurface antenna with triple-mode excitation for Sub-6 GHz applications

This paper presents a single-fed triple-mode excited low-profile broadband circularly polarized (CP) metasurface (MTS) antenna. It uses a slot-coupled circular patch antenna (CPA) to generate a narrow band of CP radiation and an MTS to broaden it. This work emphasizes a characteristic mode analysis (CMA) based systematic design approach to realize broadband CP. The CMA of a circular patch reveals the existence of orthogonal degenerated modes. A capacitive loading method separates these modes, creating a 90° phase difference for circular polarization; hence, CPA acts as a narrow-band CP radiator. For further CP bandwidth enhancement, an MTS layer is used to produce the required orthogonal modes next to the modes of CPA. The MTS is a 6×6 array of slotted circular MTS elements, which provides only the desired polarized modes (here, horizontal mode) to cascade with the CPA modes. Consequently, the cascaded modes of CPA and MTS remain mutually orthogonal with proper phases, and the excitation of these modes exhibits a wider axial ratio bandwidth (ARBW). The overall dimension of the fabricated antenna is 0.8[Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] (where [Formula: see text] is the free space wavelength at 6.2 GHz). The antenna exhibits an impedance bandwidth of 36.6% (5.18-7.4 GHz) and an ARBW of 26.16% (5.48-7.05 GHz). The design is fabricated using an FR-4 substrate and measured for validation. Being a low-cost design with a broad ARBW, it becomes promising for various sub-6 GHz wireless applications.