Eigenvalue-engineered metasurface antenna for broadband circular polarization based on characteristic mode theory

A compact metasurface-integrated circularly polarized (CP) antenna operating in the C-band is presented using a rigorous Characteristic Mode Analysis (CMA) framework. The proposed design exploits eigenvalue engineering of surface currents to realize near-degenerate orthogonal modes with stable phase quadrature, enabling broadband CP radiation. A circular polarization source (CPS), based on a square slot with a diagonal perturbation, excites orthogonal modes, while a diagonally symmetric slot-loaded metasurface (MS-2) enhances modal coupling and radiation efficiency. The metasurface reshapes the eigenvalue spectrum by compressing modal spacing and increasing modal significance, resulting in improved impedance bandwidth (IBW), axial ratio bandwidth (ARBW), and gain. The antenna achieves 46.91% IBW, 20.26% ARBW, and a peak gain of 9.7 dBi with stable broadside radiation. Experimental results show good agreement with simulations, validating the CMA-driven design methodology. The proposed approach establishes a direct link between modal physics and antenna performance, offering a compact and scalable solution for next-generation wireless and satellite communication systems.