| Since successfully developing the world’s first high-speed maglev train in Germany,maglev technology has achieved good research results in Britain,Japan and China.Compared with ordinary trains,maglev trains have the advantages of fast travel speed,low energy consumption and high safety performance.In order to reflect the above advantages and enhance the competitiveness of maglev trains,a stable and efficient wireless communication system plays a vital role.Millimeter wave wireless communication is the mainstream train-ground communication method of high-speed maglev trains,and train antennas are the key components.At present,the millimeter wave antennas in the train-ground communication system are developed by German technology on the maglev train lines operated and tested in China(such as the Shanghai Maglev Test Line).The antenna has been domestically studied,but the main technical route and the form of the antenna have not been improved.This type of antenna based on reflective antennas can meet the communication requirements to a certain extent,but the main disadvantages are the large size and high height of the antenna.The large size and height have a great impact on the operation and aesthetics of the train.Therefore,this paper proposes to develop a new type of high-speed maglev millimeterwave train-ground communication system based on array antennas,to study the miniaturization of train-mounted antennas,to master the miniaturized independent design method of train-ground antennas in train-ground communication systems,and to develop miniaturized train antennas that meet the requirements.This paper mainly studies the small waveguide spiral array antenna based on millimeter wave vehicle-to-ground communication.The main work is divided into the following aspects to elaborate:1.Design and analysis of miniaturized side-feeding waveguide spiral array antenna.A side-fed waveguide spiral array antenna was proposed.Designed the design of millimeter wave band(37GHz ～ 39GHz)low-profile element helical antenna;designed the design of coupled probes and fixed structures;The size achieves approximately equal amplitude output at a center frequency of 38 GHz.The radiation characteristics of the 30-element sub-array were studied using full-wave electromagnetic simulation software.Simulation results show that at a center frequency of 38 GHz,the gain is 22.4 d B,the axial ratio is 1.6 d B,an elevation plane beam width of 4.2o,and an azimuth plane beam width of 30.2o;in the band of 37.0～39.0GHz,the reflection coefficient of this antenna is less than-15 d B,and the antenna gain is greater than21.5d B.Due to the form of side feed,when the operating frequency deviates from the center frequency,the phase difference between adjacent units will change,causing the beam pointing to shift,the axial gain is reduced,and broadband operation cannot be achieved;at the same time,it is found that the It is difficult to adjust the coupling amount of the unit,require high accuracy,and narrow the frequency band with better output imbalance.2.Improved design and analysis of miniaturized waveguide spiral array antenna.In order to improve the shortcomings of the side-feed form,the layout of the array was redesigned,and the form of using a simpler coaxial waveguide center feed and four-way rectangular waveguide parallel feed was improved to solve the beam pointing deviation when the operating frequency shifted from the center frequency The problem of shift and axial gain reduction.In the design of the feed system,the cross-sectional size of the rectangular waveguide is changed and the waveguide coaxial converter is used to solve the problem of the difficulty of coupling the probe in the rectangular waveguide,and the approximately equalamplitude feed of each output port is realized.The effect is analyzed by using full-wave electromagnetic simulation software.The results show that in the band of 37-39 GHz,the standing wave coefficient is less than 1.35,the antenna can achieve axial radiation,the gain is greater than 21.9d B,and the axial ratio is less than 2.5d B,it can achieve better circularly polarized radiation.An elevation plane beam width is between 4.3 ° and 4.6 °,and an azimuth plane beam width is between 30.0 ° and 31.0 °.On this basis,the development and experiment of a single pair of antennas are carried out.The results show that the antenna is in the band of37-39 GHz,the antenna standing wave ratio is less than 1.41,the gain is greater than 21.7d B,the axial ratio is less than 3.6d B,and an azimuth plane beam width is 4.5 ° ～ 4.7 °,an elevation plane beam width is 29 ° ～ 29.7 °,which meets the design requirements of vehicle-mounted antennas in millimeter-wave vehicle-ground communication systems.Finally,the experimental verification scheme of the vehicle-mounted antenna under the current condition of the maglev train is given.By using electromagnetic simulation software to establish the experimental model of the current vehicle-mounted antenna of the maglev train,the experimental feasibility of the scheme is described.At the same time,based on the above experimental scheme,the installation scheme of the array antenna in the current train is given.3.Preliminary design and research of miniaturized waveguide spiral array shaping for millimeter wave train-ground communication.In order to improve the performance of the array antenna,by increasing the number of elements,the gain can be increased within the original 3d B beam width,and the gain of the array antenna can be increased in the axial direction.Meet the performance index of the train-ground antenna.By increasing the number of azimuth plane elements to 4 and 6,using the shaping algorithm,the amplitude and phase distribution results of 4 elements and 6 elements are obtained,and the performance of the layout is analyzed by simulation.According to the optimal amplitude and phase distribution of the formed array,determine the array layout of 6 × 14 units,and design the feeding system accordingly.The design of the feed system of the 6 × 14 array antenna adopts the cascading method,which is mainly composed of 1-2 power splitters,1-3 branch and waveguide coaxial converter cascade to form a 12-way power splitter It has been optimized for design.The simulation results show that within the range of 37 GH ～ 39 GHz,the reflection coefficient of a 12-way power splitter is less than-16.3d B,and the output amplitude values of each port satisfy the relationship of 1: 0.48: 0.4.Add the probe to the feed system,and through simulation calculation,the reflection of the feed system is less than-16 d B.The amplitude value of each port approximately satisfies the relationship of 1: 0.48: 0.4,which proves the feasibility of the feeding system. |
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