Dual-broadband highly efficient reflective multi-polarisation converter based on multi-order plasmon resonant metasurface

In this study, a dual-broadband reflective polarisation converter with high efficiency for both linear-to-linear and linear-to-circular polarisations based on a metasurface is proposed. Owing to the characteristics of strong anisotropy and multi-order plasmon resonances, the proposed polarisation converter can rotate any/xpolarised electromagnetic wave to its cross-polarised (x/y) direction in the lower frequency band of 7.74-14.44 GHz (a fractional bandwidth of 60.4%) with over 0.9 polarisation conversion ratio. Besides, the proposed structure can also convert a linearly polarised incident wave to a circularly polarised one after reflection in the higher frequency band of 14.95-17.35 GHz (a fractional bandwidth of 14.9%). The performance in the two bands can be controlled separately by altering the proper parameters of the structure. Numerical analysis is used to predict the polarisation states of the proposed polarisation converter. Moreover, the physical mechanism of multiple resonances is discussed based on surface current distributions. A prototype of the polarisation converter is fabricated and measured. A reasonable agreement between the experiments and simulations is obtained. The design has a simple and scalable geometry, and is a good candidate for polarisation control devices in microwave, terahertz and optical frequency regions.