Single-Layer Multimode Broadband Circularly Polarized Reflected Element Using Characteristic Mode Analysis

A broadband structure of multimode operation by introducing nonuniform round magneto-electric (ME) dipole is proposed to improve the bandwidth of single-layer broadband circularly polarized (CP) reflected elements. The multimode radiation mechanism of the broadband element is analyzed and verified using characteristic mode analysis. Guided by the proposed method, a single-layer broadband CP-reflected element working in Ka-band is proposed, which achieves a bandwidth of 67% from 19.2 GHz to 38.4 GHz for −15 dB cross-polarization reflection. A reflectarray antenna (87.02 mm× 68.7 mm) is designed, fabricated, and measured with an existing CP feeder. A good agreement between the simulation and the measurement is achieved, and a 33.85% 3 dB AR bandwidth (27 GHz to 38 GHz) and a 35.29% 3 dB gain bandwidth (28 GHz to 40 GHz) of the proposed reflectarray are demonstrated due to the limitation of CP feeder, respectively. The proposed design method is not limited to the ME dipole structure and can be extended to other CP reflectarray antenna designs.