Quasi-continuous linear phase-gradient metamaterial based on conformal spoof surface plasmon polaritons

Abstract

In this work, we propose a method of achieving quasi-continuous linear phase gradient for transmitted waves based on conformal spoof surface plasmon polariton (SSPP). To this end, a SSPP structure with high transmission is firstly designed as the unit cell of the metamaterial. To obtain the phase gradient, SSPP structures are arranged delicately in a way that they are conformal to the brachistochrone curve. In this way, quasi-continuous linear Pancharatnam-Berry (PB) phase profile can be realized strictly along one of the two transverse directions. To verify this idea, a dual-band transmissive metamaterial operating in X and Ku band was designed, fabricated and measured. Due to the phase gradient imparted by the conformal SSPP structures, high-efficiency anomalous refraction can be realized within the two bands. Different from the general PGM, the phase gradient of the conformal SSPP structure allows us to achieve the desired anomalous refraction angle without reconstructing the PB phase. Both the simulation and measurement results are well consistent with theoretical predictions. This work provides another strategy of achieving anomalous refraction and may find applications in beam steering, digital beam forming, etc.