Research On Directional And Omnidirectional Circularly Polarized Antenna Based On Metasurface

The quality of antenna became particularly important under the rapid development of wireless communication technology nowadays,because the performance of antenna directly affect the quality of communication system.Comparing with linearly polarized antennas,circularly polarized antennas can reduce the influence of polarization mismatch and multipath effects effectively.The application of antenna is different in different scenes.The antenna can be divided into directional antenna for centralized signal transmission and reception and omnidirectional antenna for all directional signal transmission and reception.Metamaterial,as artificial composite materials or structures,has physical properties beyond the natural world,and its two-dimensional manifestations—metasurfaces,it can not only control electromagnetic waves,but have great structural design space,so metasurface has huge application value.Therefore,an in-depth study on the directional circular polarization and omnidirectional circular polarization antenna base on metasurface was carried out in this paper and the research results can be summarized as follows:(1)Design of broadband circularly polarized metasurface antenna based on dual-pentagonal units.Firstly,the polarization rotation characteristics of the chamfered element and the double pentagon element were analyzed by Floquet Port.By analyzing the reflection coefficient of amplitude and phase,it can be concluded that the comprehensive field formed circular polarization by the incident wave and reflected wave of the units.Then the evolution process of the dual-pentagonal element was analyzed,from the square patch to the chamfered patch,then to the dual-pentagonal element.The S-parameters and the Axial Ratio curves were obtained,and the results show that the dual-pentagonal element can expand the working bandwidth of the Axial Ratio significantly.In addition,the mode analysis of the metasurface structure was carried out,and the modes of TM₁₀and antiphase TM₂₀make the antenna has a wider impedance bandwidth.(2)A low profile omnidirectional circularly polarized antenna based on metasurface.First,a pair of orthogonal slots were etched on the basis of the circular patch form 4 fan-shaped units,and then a pair of orthogonal slots along diagonally direction were etched on top of the 4 fan-shaped unit structures,and a circular gap was etched around the middle of the fan-shaped unit.The whole evolution process was studied and analyzed by the TCM,the current distribution and far-field radiation characteristics of different modes were observed,orthogonal TM₂₁modes were selected finally.To keep the amplitudes and phases of the four ports equal,a Wilkinson power divider was used to couple the energy with equal amplitudes and phases for the four paris cross slots.The unequal length cross gap on the metallized floor makes the amplitude equal,form a 90°phase difference of the two modes,so omnidirectional circular polarization performance was achieved.