Abstract: A wideband circularly polarized metasurface antenna with single-layer lowprofile, based on coplanar waveguide (CPW) feeding structure, is proposed in this paper. Characteristic mode theory is employed to guide the antenna design, revealing the working principle of the antenna. Firstly, the metasurface structure is analyzed, and two target modes with a phase difference of nearly 90° and good radiation directivity are successfully identified. To excite the target modes, a reasonable feeding structure is designed based on the results of characteristic mode analysis. A CPW feed line is utilized to simultaneously excite the two modes, resulting in a single-layer antenna structure without requiring additional dielectric substrates. The final antenna dimensions are 1.05λ₀×1.05λ₀×0.69λ₀, exhibiting a low-profile configuration. At the same time, branches are loaded at the end of the CPW coupling aperture for impedance matching, and the relative impedance bandwidth of the antenna is 27% (5.71 GHz~7.50 GHz). Furthermore, tilting the CPW coupling aperture introduces phase compensation to the operating modes, effectively improving the circular polarization performance. The resulting 3 dB axial ratio bandwidth is 16.6% (6.12 GHz~7.23 GHz), with stable gain observed within the operating band.