Broadband reconfigurable reflective polarization convertor

With the rapid evolution of radar technology and mobile communication systems, polarization conversion has received much attention from academia and industry in recent years, which has the advantages of improving system performance through eliminating multipath fading. In this paper, a novel broadband reconfigurable reflective polarization convertor is designed, which combines the idea of metamaterial and the technology of micro-electro-mechanical system (MEMS) switches. The proposed structure consists of three layers: an upper metallic patches layer, a middle dielectric layer with a thickness of 2 mm, and a bottom metal plate. There are through-holes of metal connecting the upper and bottom layers. According to the simulation using HFSS software, when the MEMS switch is on, the device works with a relative bandwidth of 57.77% from 7.78 GHz to 14.10 GHz, of which the polarization conversion ratio is larger than 80%. In addition, at 7.62 GHz and 12.56 GHz, the reflected wave is a right-hand circularly polarized wave and a left-hand circularly polarized wave, respectively. When the MEMS switch is off, the reflected wave is in the same polarization, which means the device does not convert the polarization of electromagnetic wave anymore. The electromagnetic wave are decomposed into the u-v coordinate system to further understand the wideband polarization rotation. The reflection phase and the surface current distributions of the convertor are analyzed. Then, the working principle of polarization rotation is explained by analyzing the current distributions and explaining the theory from three different viewpoints. Finally, a 1225-cell (35×35) prototype is fabricated to verify the simulation results. The measured curve has three resonant frequencies and shifts towards the lower frequency slightly. The discrepancy between simulations and measurements is mainly attributed to the restriction of fabrication and measurement condition. In general, experimental results are in agreement with the simulations: when linear polarized wave is incident, the reflected wave realizes the transition from co-polarization to cross-polarization as the switch is switched from off to on. The proposed reconfigurable polarization rotation surface has advantages of broadband, low loss and ease of fabrication, which has great potential applications in antenna radiation, reducing the radar cross section and other territories in controlling electromagnetic wave dynamically.