Generation And Regulation Of Electromagnetic Vortex Beams Based On Array Synthesis

With the rapid development of communication technology,expanding the channel capacity of wireless communication has become the main goal of solving spectrum congestion.The mode multiplexing characteristics of vortex beams carrying orbital angular momentum(OAM)have brought broad prospects for channel capacity expansion.Therefore,electromagnetic vortex waves with OAM have gradually become the research hotspot.The rotation factor carried by the vortex wave makes its wave front plane distribute as spiral,and it travels forward along the transmission axis.The vortex beams with different mode have orthogonality,which makes it possible to transmit multiple channels of information in the same frequency band,and the channels are independent of each other.However,traditional electromagnetic vortex beam communication still has many challenges.The divergence characteristics of orbital angular momentum vortex beams limit its long-distance information transmission.And in the case of multiplexed beam communication,the sidelobes interference will affect the integrity of the OAM information and reduce the mode purity.Similarly,the beam radiation direction is not controlled.In this thesis,the vortex beam generation method is researched and designed in order to solve these problems.In the practical application environment,the array synthesis method is used to design the different arrays to generate vortex beam and improve the vortex wave quality.The main work of this thesis is as follows: 1.Generation of low sidelobes normal vortex beam which based on the multiplexed uniform circular array(UCA).Firstly,combining the comprehensive theory of circular array and the OAM design principle,a normalized Bessel function form of multi-circular array factor is proposed.By changing the position and number of array elements,the objective function of sidelobes gain function can be adjusted;Secondly,the objective function is optimized and analyzed by genetic algorithm,and the array parameters of the low sidelobes vortex beam at the specified divergence angle are obtained.Later,a circularly polarized microstrip antenna with center feed is proposed.The patch has an uneven U-shaped slot,which can be used for feed compensation by using its rotation characteristics;A circularly polarized microstrip antenna with center feed was used to construct the array and feed network.After simulation analysis and processing verification,under the same beam divergence angle,the design increases the isolation and maintains the polarization characteristics.The sidelobes problem in the case of vortex beam normal communication is solved.2.Generation of deflected vortex beams with low sidelobes based on tapered feed.Firstly,combining the Chebyshev distribution and the normal OAM array,the effect of changing the feed amplitude form on the beam sidelobes is investigated.The multi-beam communication effect can be numerically simulated.The results of beam deflection verify the sidelobes effect on the efficiency of the main beam.After analyzing the theory of square array and tapered distribution,the center-fed microstrip unit is used to design an array to generate deflected vortex beam with low sidelobes.Based on the above research,the simplified array is designed by quantizing the feed amplitude,and the distribution characteristics of beam sidelobes of different schemes are studied.Later,two types of feeding networks with equal power distribution are designed for the array.After simulation analysis and processing measurement,it is found that the isolation of the main and side lobes of the +1 mode vortex beam with the deflection angle of 30 degree has been improved,which can reduce the impact between beam multiplexed communications.3.Vortex beam regulation based on artificial electromagnetic metasurface.Firstly,a multi-layer transmission structure is used to form a planar array periodically.The horn is placed in space as a feeding source,and the size of the planar array unit is calculated by the phase parameter.The phase of the planar array consists of the feed compensation and the orbital angular momentum,and the +1 mode beam simulation results are analyzed.Then,the beam scanning angle is modulated by a cone lens,and the influence of the directional pattern and coverage area of OAM mode is studied.Then,the accuracy research is further optimized.The new unit structure is used to reduce the reflection of the planar array,and larger electric size of aperture enhances the beam radiation directivity.Simulation results prove that the array can achieve OAM vortex beam scanning of high precision for communication applications.