A Reconfigurable Multi-mode Orbital Angular Momentum Antenna Based On Tensor Metasurface

The technique of orbital angular momentum modulation provides a solution to the problem of spectrum resources and it makes use of the orthogonality between different modulation modes to realize the sharing of spectrum resources and greatly improves the utilization rate of spectrum resources.At present,there are two main methods of the ring phase distribution array antenna and the metasurface to modulate the orbital angular momentum of the beam in microwave frequency band.The orbital angular momentum modulation antenna using the method of circular phase distribution array can be reconfigurable by designing the feed network,but the radiation elements of the array are relatively bulky and the gain is not high.However,the orbital angular momentum antenna realized by the metasurface has high gain and simple feeding network,but its orbital angular momentum modulation mode is too single.The design of the reconfigurable multi-mode orbital angular momentum antenna based on tensor metasurface is presented in this paper.The tensor metasurface is composed of anisotropic tensor impedance units arranged according to the interference superposition formula of object field and source field which is similar to the optical holography.It has the advantages of easy control of the polarization mode and radiation angle of the object field,and can superimpose multiple object fields onto the same interference plane to achieve the radiation of multiple object fields.In addition,there are many designs to realize orbital angular momentum modulation by means of metasurface,but the orbital angular momentum modes realized after the design is completed are all fixed and can not be changed flexibly.In order to solve this problem,this paper explores the design of reconfigurable orbital angular momentum modulation for tensor holographic impedance modulated surface antenna at 10 GHz.First of all,in order to design the tensor metasurface,the parameters of the tensor impedance unit are simulated by dispersion curve scanning,and then the database of the tensor impedance unit can be calculated.A tensor holographic impedance modulated surface antenna for left-handed circularly polarized double beam radiation is designed by means of theoretical design formula and database principal axis matching method.Then,the orbital angular momentum modulation technology is added to realize the left-circularly polarized dual-beam dual-mode radiation antenna and left-circularly polarized normal high-order modes radiation antenna respectively based on the tensor holographic impedance modulated surface antenna.Finally,the left-circularly polarized normal radiation tensor metasurface antenna without orbital angular momentum modulation is used as the radiation element of the reconfigurable multi-mode orbital angular momentum antenna.The initial phase gradient of the six radiating elements can be changed by rotman lens and rotation characteristics of the radiating element respectively,and realize the reconfiguration of five orbital angular momentum modulation modes.Moreover,the number of radiation elements is also expanded to study the reconfiguration of higher order orbital angular momentum modulation modes.