Nonuniform metasurface for wideband circularly polarized antenna using characteristic mode analysis

This paper proposes a nonuniform metasurface-based circularly polarized antenna utilizing characteristic mode analysis (CMA). The initial antenna is a corner-cut and slotted patch connected to the ground plane with a metal-via. By arranging 45° rotated slotted patches around it, CP radiation is achieved, forming a nonuniform metasurface. Through CMA, two satisfied CP modes are obtained by merging mode 1 and 4, as they exhibit similar far-field radiation patterns and surface current directions. Simulation results show that the proposed antenna has an S11 ranging from 4.1 to 5.7 GHz, a 3 dB AR bandwidth of 4.4–5.3 GHz, and an average 2 dB higher gain than the initial antenna with a maximum of 11.4dBic. The radiated mechanism is investigated to explain the bandwidth broadening caused by the arrangement of the 45° rotated slotted patches. It is found that the excitation of two orthogonal modes results in CP radiation and a wider bandwidth. Furthermore, a 2 × 2 array with sequential rotation is proposed to enhance the radiation properties. Simulated and measured results show that the antenna array achieves an S11 of 4–6.08 GHz, a 3 dB AR bandwidth ranging from 4.3 to 6.2 GHz, and a peak gain of 15.2 GHz, with a low profile of 0.08 λ0. A LHCP antenna can also be achieved through slight adjustment, making the proposed antenna suitable for military and civilian communication, and point-to-point links.