Research On Generation And Transmission Technology Of Vortex Electromagnetic Wave

With the rapid development of wireless communication technology,how to use the limited spectrum resources,maximize the communication rate and communication capacity,and solve the increasing communication needs has been a key issue for people to study.In recent years,vortex electromagnetic waves with orbital angular momentum have realized multiple transmissions in the same frequency band,which can greatly improve the utilization rate of the frequency spectrum.Therefore,it has become the focus of research.This thesis focuses on the generation method of vortex electromagnetic waves generated by array antennas,and proposes an analysis method based on multi-loop array synthesis.This method is applied to concentric dual-loop circular array antennas.The optimization of the design allows the vortex electromagnetic waves generated by the inner and outer rings to have the same divergence angle,thereby reducing the complexity of the receiving end.And combining this dual-ring array with the Butler matrix of the multiple-input multiple-output structure,it can generate multiple modes of vortex electromagnetic waves at the same time,which is simpler and more convenient than ordinary feed networks.In addition,the problem of a single vortex electromagnetic wave mode generated by the circular array antenna has also been solved,and a mixed mode for multiplexed communication can also be realized.In the design of the Butler matrix,we optimized the traditional 4×4 Butler matrix and the 8×8 Butler matrix.By changing the position of its input and output ports,the use of a part of the cross coupler was eliminated,which simplified the design and reduced Size,and also reduce losses.The phase shift lines with a phase gradient of-45°and-22.5°are added at the output ports to generate a multi-mode vortex electromagnetic wave.Simulation results show that the designed Butler matrix has the good phase and amplitude consistency in the working frequency band.At the same time,this thesis also proposes a new idea.Through the analysis of characteristic mode theory,a single antenna device capable of generating vortex electromagnetic waves is proposed.The characteristic current generated in the patch antenna is analogized to an electric dipole.Using the idea of mode current splicing,the two sets of complementary characteristic currents are superimposed into an array model to generate vortex electromagnetic waves.Therefore,based on the characteristic mode analysis,a dodecagonal patch antenna capable of generating vortex electromagnetic waves is proposed.It is fed with a 3d B coupler,so that this patch antenna can generate vortex electromagnetic waves with different OAM modes.In addition,it can generate mixed-mode vortex electromagnetic waves for multiplexed communication.At the same time,using the designed patch antenna for array analysis,simulations show that the OAM mode of the unit and the OAM mode of the array can be linearly superimposed,breaking the situation of the limit number of array elements.The feeding network of the 4×8 Butler matrix designed above is also fully utilized to generate multiple modal vortex electromagnetic waves by inputting to different ports.Finally,a helical antenna unit is designed and array analysis is performed to further prove the superposition of the unit OAM mode and the array OAM mode.The feeding network uses the 2×4 Butler matrix.This not only provides miniaturized and multifunctional equipment for wireless communication based on vortex electromagnetic waves,but also provides new ideas for the analysis and application of a single patch antenna,and also provides an effective way for the generation of higher-order modes.Finally,the thesis studies the transmission characteristics of vortex electromagnetic waves.We mainly compare the transmission characteristics of ordinary circular arrays,single antennas,and single antenna arrays in the air,analyzes the advantages and disadvantages of ordinary circular array devices that generate vortex electromagnetic waves,and single antenna devices.Compared with a common circular array that produces the same mode,the size of the single antenna array is still small and the feeding network is simpler,but at the same time,it can maintain good transmission characteristics compared to a single antenna.The generation method of vortex electromagnetic waves is worthy of research and exploration.Finally,the propagation characteristics of plane electromagnetic waves and vortex electromagnetic waves in plasma are also studied.According to the actual plasma generating device,an equivalent model is established in HFSS for approximate simulation and analysis.