Research On Radiation Characteristics Of Novel Planar Orbital Angular Momentum Antenna

In recent years,due to the rapid development of communication technology and the continuous growth of communication services,the shortage of spectrum resources has been difficult to meet various application scenarios.In this context,the orbital angular momentum electromagnetic wave with vortex phase wave front has gradually attracted the attention of domestic and foreign scholars due to its potential channel reuse capability.By using the orthogonality between the OAM beams carrying different modes,the OAM beams can be modulated at a certain frequency to realize simultaneous transmission of multi-channel signals,so as to improve the spectrum utilization and channel capacity of the system and provide a new solution to the congestion problem of radio frequency band.The orbital angular momentum antenna is an indispensable device for transmitting and receiving OAM electromagnetic waves.Among them,the OAM antenna with a planar structure can be well integrated with other modules in the communication system,and it is also suitable for mass production,which can meet the requirements of integration and miniaturization.Combining the classical antenna theory with the existing OAM antenna technology,three planar OAM antennas are proposed in this paper,which further improves the degree of freedom in the design of the orbital angular momentum antenna and the flexibility in applications.Firstly,the theory of orbital angular momentum correlation is expounded,and the main generation methods of OAM beams in radio field are introduced and summarized,which lays a foundation for the design of OAM antennas with planar structures.Aiming at the problem that the traditional OAM antennas have single mode,an OAM antenna based on a planar equiangular spiral is proposed.By setting equal amplitude,different continuous phase difference feeds to the proposed antenna structure,the OAM beams with modes l?28?0,-1,-2,-3 and l?28?1,0,-1,-2,-3,-4 can be generated at 5.8 GHz using planar four-arm and six-arm equiangular spiral antennas without changing the antenna structure respectively.Finally,the planar four-arm equiangular spiral antenna is machined and the measured near field phase distribution is consistent with the simulation results.Based on the related mechanism of the OAM beam generated by the circularly polarized patch,a single-feed circularly polarized OAM antenna with a compact structure is proposed,which can work in a specific TM_nm mode at 5.8 GHz by adjusting the relevant size parameters.By numerically simulating and optimizing the antenna,the relevant results of the left-handed circularly polarized antennas working in the modes l?28?0,1,2 are given.And by changing the position of the feeding point,the antenna can radiate the right-circularly polarized beam with modes l?28?0,-1,-2.Finally,a double-mode circular polarization OAM antenna with mode l?28??1 was machined to achieve the radiation of double-mode and double-circular polarization beam,and relevant tests were carried out.Based on the antipodal Vivaldi unit,an OAM radial circular array is proposed.OAM beams with different modes can be generated at 5.8 GHz by feeding the eight antipodal Vivaldi units with equal amplitude and different continuous phase differences.In order to achieve power distribution and continuous phase differences between units,two feeding networks based on corporate microstrip lines were designed,and physical processing and related tests were performed on radial circular arrays in two modes.