Design And Research On The Broadband Micro-strip Antenna For The GSM-R Band Of The High-speed Trains

The main purpose of this paper is to design an antenna for the GSM-R signal test in the train. The frequency band of the antenna is from 885MHz to 935MHz. The antenna's parameters need satisfy that the voltage stand wave ratio VSWR≤2 (Return loss S11≤-10dB), the maximum gain more than 3 dB, and the half-power bandwidth of main lobe more than 60°in the frequency band. Considering the portability of testing in the train, the wide broadband micro-strip antenna is adopted to realize the objective for its smaller structure. Therefore, first the paper introduced the basic theory and analysis methods of the micro-strip antenna, and then simulated the antenna model by HFSS software. After that, the author deeply studied and improved the equivalent dipole antenna structure, and designed a new type broadband antenna which met the above parameters. Finally, the practical manufactured antenna was measured by the antenna measurement system, and the antenna patterns had some errors between measured results and simulated results. The author analyzed the reason of the errors.The main work and innovation of the paper are as follows:First of all, the paper introduced the basic theory of micro-strip antenna, which contained definition, structure types, advantages, disadvantages, applications, radiation theory, feed methods and broadband technologies etc.Secondly, the paper presented three commonly analysis methods, including Transmission line method, Cavity model theory, Finite element method, which provided a theoretical basis for the micro-strip antenna design.Thirdly, according to the antenna's performance parameters, the paper introduced a new designed micro-strip antenna which worked from 782MHz to 938MHz, and the relative bandwidth reached to 18.82%. The entire design process was beginning with the typical rectangular micro-strip patch antenna, and then according to the antenna theory, the micro-strip patch antenna was improved to the equivalent dipole antenna so that it kept the broadband characteristics. For solving the multiple directions of the equivalent dipole antenna, the structure of the equivalent dipole antenna was optimized and improved to make the micro-strip antenna keep bandwidth and good performance of directional at the same time, on the basis of the inverter and director of the antenna theory. And ultimately each size of the antenna was determined. Meanwhile, the author deeply studied the influence of the physical parameters. The entire design process was simulated by HFSS software.Finally, based on Transmission line theory, the author proposed a method for measuring the relative permittivity of medium plate. The antenna's parameters (voltage standing wave ratio, radiation pattern, gain, antenna factor etc.) were measured in anechoic chamber through the antenna measurement system. Compared with the simulated results, the measured results were in good agreement with the exception of the antenna patterns. And the author analyzed the cause of the errors.