Design of low-profile four-modes patterns metasurface antenna using characteristic mode analysis

In this paper, we propose a novel design approach for multi-mode antenna radiation patterns using characteristic mode (CM) theory. Specifically, we observe that the response of the multi-mode radiation pattern is a superposition of modal current responses, which can be controlled through port excitation. By combining the port excitations, we achieve the desired multi-mode radiation pattern. The feed structure can also be designed using CM theory. The validity of this intuition is confirmed through CM analysis. Subsequently, we use the proposed theory to design an antenna structure with a profile height of 0.07 lambda(0) (lambda(0) is the wavelength of the electromagnetic wave at 2.8 GHz in vacuum). This antenna is capable of achieving four orthogonal radiation patterns. Simulation and measurement of the antenna demonstrate that the four radiation patterns can operate simultaneously within a bandwidth of 17% (|S-11|<-10 dB), with worst-case port isolation of -24 dB.