This paper presents a broadband metasurface (MS) antenna designed through characteristic modes analysis. By introducing horizontal slots into a 3 × 3 MS array, a pair of degenerate modes is successfully separated and the dominant mode is reconfigured as TM10 mode. Optimizing feed position simultaneously excites the TM10 modes of both the patch antenna and the MS, expanding the −10 dB impedance bandwidth from 4.09–4.22 GHz to 3.45–4.5 GHz with a gain variation of less than 1.9 dB. Furthermore, a dual-port multiple-input multiple-output (MIMO) antenna is constructed by orthogonally arranging two elements. The exclusive TM10 mode enables inherent decoupling, achieving over 23.6 dB isolation. Measured results exhibit good agreement with simulations, demonstrating an operational band of 3.44–4.39 GHz, effectively covering the 5G NR (New Radio) n48 band.
