The Design And Analysis Of Wideband Spiral OAM Antenna

At present,most of the reported antennas have relatively narrow bandwidth,and the high mode purity cannot be maintained within the wide frequency band,a high data transmission rate cannot be obtained in an actual OAM communication system.Therefore,it is very necessary to design a broadband OAM antenna for the application of OAM in the RF communications.The spiral OAM antenna designed in this paper not only has the advantage of wide band,but also maintains the high purity mode of the beam.In addition,the feeding network is simpler than the array antenna and the manufacturing process is simple.Therefore,it has great potential for OAM communication at radio-frequency in the future.In this paper,we design a spiral antenna to generate OAM beams.Firstly,the helical antenna with single arm is modeled and analyzed,and the theoretical calculation and electromagnetic simulation are carried out to verify that the beam carrying with orbital angular momentum can be generated by designing the pitch and radius of the antenna reasonably.Due to the radiation of the OAM beam is not uniform and the mode purity is relatively lolw.A centrosymmetric helical structure with three arms is adopted here to solve the problem.The antenna is fed by an one-third microstrip power splitter.Finally,after a series of electromagnetic simulations and experimental measurements,the simulation bandwidth can get to 2.8 GHz in 10 GHz and the relative bandwidth can reach up to 28%,the experimental measurement results show that the operating frequency is from 9.4 GHz to 14,2 GHz.The radiation field has a spiral shape of the phase distribution,and the intensity at the center of the beam has a minimum value.It is all proved that an orbital angular momentum beam with mode 3 is generated within a wide frequency band.Furthermore,in order to ensure the quality of the generated OAM beam,the OAM spectrum of the beam are analyzed by using the Fourier transform,and the influence on the main mode purity of helical OAM antenna with different structures was also discussed.The simulation results show that the main mode purity of the OAM beam remains above 90%over a wide frequency band.It is confirmed that the helical OAM antenna can produce an OAM beam with high-purity.In the experimental results,the main mode purity can reach up to 60%at the main resonance frequency is displayed,which is caused by unavoidable external factors,such as the manufacturing process of the antenna and the misalignment of the transmitting and receiving antennas in the measurement.