Design And Research Of Millimeter Wave Communication Antennas Between Urban Rail Trains

In view of the high maintenance cost and large information transmission delay of the existing urban rail transit system,many scholars have gradually carried out research on point-to-point direct communication between dual mobile terminals,and Train to Train(T2T)communication technology has emerged as the times require.The train communication system based on T2 T communication has the advantages of short transmission time,strong system flexibility and low operating cost,and has become an important direction for the development of urban rail transit in the future.In the T2 T communication system,point-to-point information interaction is carried out between trains,and the antenna is an important part of wireless signal transmission and reception.The existing train-mounted antennas are mainly topped disc antennas and topped antennas.These antennas have problems such as poor directivity,short communication distance,and low communication frequency bands,and are not suitable for train-to-train communication systems.Because the subway environment is mostly tunnel,the propagation of electromagnetic waves will be affected by multipath effects and waveguide effects.The former will cause serious attenuation of electromagnetic waves,while the latter has a certain frequency selectivity to electromagnetic waves,which seriously affects the performance of communication systems.Millimeter wave has the advantages of high speed,low delay and short antenna.Therefore,it is necessary to introduce millimeter wave technology into T2 T to carry out the research of T2 T communication antenna.The main contents of the thesis include :A single antenna with a large gain is studied for communication environments with short tunnel distances.Firstly,determine the antenna frequency band and gain.Through the selection of existing antennas,determine that the horn antenna is the antenna of the T2 T communication system,and obtain the far field radiation pattern of the antenna,thereby designing a millimeter wave conical horn antenna for direct communication between urban rail trains;Secondly,based on traditional empirical formulas and electromagnetic simulation software HFSS(High Frequency Structure Simulator),modeling and simulation are conducted to obtain the characteristic parameters of the antenna.Through comparison,the influence of the opening diameter and waveguide size of the horn antenna on the voltage reflection coefficient is obtained;Finally,an improved genetic algorithm is used to optimize the antenna structure to optimize the waveguide size and opening diameter parameters.The simulation results show that under the main frequency of the antenna,the optimized antenna gain is 22.2d B,the voltage standing wave ratio is 1.01 and has good directionality,which meets the requirements for high gain and strong termination capability of the train antenna in the train direct communication system.Secondly,in order to improve the tunnel communication quality with a large curvature radius,the antenna array is designed.The basic element is improved,the probe is added,and the optimal height and length of the probe are obtained through simulation analysis.In order to improve the quality of tunnel communication with a large radius of curvature and long distance,an array antenna is designed.Firstly,due to the excessively large opening diameter of a single antenna,when designed as an array,large side lobes may be generated.Therefore,the conical horn antenna is improved by replacing a circular waveguide with a square waveguide and feeding the horn antenna using a microstrip line probe.The optimal probe height and probe length are obtained through simulation analysis;Secondly,summarize the feeding characteristics of three different array antennas and determine the final feeding method based on design requirements;Then,combined with the improved horn antenna,the simulation analysis of three different array transmission lines shows that the horn antenna has a maximum gain of 8.36 d B and a lower voltage reflection coefficient under microstrip line transmission;Finally,the number and spacing of array elements are obtained through gain requirements to determine the array surface,and then the array model is designed.The simulation results show that the antenna array gain is 28 d B,and the voltage reflection coefficient is less than-15 d B.Its performance can meet the communication requirements between train systems,providing a new idea and solution for urban rail transit communication in long tunnels.