Research On Design Evaluation And Validation Method Of Microwave Anechoic Chambers

Microwave anechoic chamber with electromagnetic interference shielding materials shielding outside,absorbing material to inhibit the internal electromagnetic multipath interference,the combination of the two to obtain a relatively quiet electromagnetic measurement environment.It can provide low level and constant electromagnetic environment,improve the accuracy and reliability of measurement.In the city rail transportation,wireless RF transmission device has a wide frequency range(0.5GHz-6GHz),transmission diversity(directional antenna,coaxial cable,leakage waveguide)characteristics of ordinary microwave anechoic chamber can not meet the needs of our measurements.To build a microwave anechoic chamber dedicated for RF equipment test of city rail traffic,and reduce the wireless electromagnetic interference effects on the test results,it is helpful for us to analysis the performance of the equipment more accurately.This paper mainly studies the design of microwave darkroom equipment for RF city rail traffic measurement,assessment and verification methods.The specific research contents of the thesis are as follows.1)Study on the design scheme for city rail transit equipment RF anechoic chamber tested.From the mode of transmission,transmission frequency analysis of the measured equipment demand for microwave anechoic chamber,quantitative calculation of the main parameters of microwave anechoic chamber,for shielding material and microwave absorbing material selection of specific parameters,design structure and measurement system of anechoic chamber are given.2)The evaluation method and evaluation process of main parameters of microwave anechoic chamber are studied.The influence of five main performance indexes,such as shielding efficiency,static reflectivity level,cross polarization,uniformity of field amplitude and multipath loss,on the measurement results are analyzed,and the specific evaluation is determined by combining the actual design conditions of microwave anechoic chamber Method and assessment process to obtain the assessment results.Compared with the results of theoretical calculation,the evaluation of micro-blog room design meets the requirements of urban rail transit radio equipment measurement.3)Analyze the antenna and leaky waveguide measurements to verify the performance of the measurement system in the microwave anechoic chamber.The maximum received level,the maximum sidelobe level,and the 3 dB bandwidth of the antenna pattern are compared with those of the standard antenna pattern.The fast Fourier transform(FFT)is used to convert the near-field measurements of the antenna to the far-field,and the 3 dB bandwidth error is compared with the far-field antenna pattern.The error of multiple measurements of leaky waveguide was analyzed.The usability and stability of the microwave anechoic chamber measurement system are verified.The results show that the measurement environment of the microwave anechoic chamber satisfies the performance requirements proposed in the design process through the evaluation of a number of performance indexes of the microwave darkroom.Compared with the standard antenna pattern,the 3dB bandwidth error is about±1 °,the maximum level of the receiver,the maximum sidelobe level error within ± 3dB,the standard horn antenna near-field measurement results into the far field,Compared with the far-field antenna pattern,3dB bandwidth of the error angle in the range of±4°to meet the engineering measurement error requirements.The error of the leakage waveguide is between±1dB,which can meet the stability requirement of microwave anechoic chamber.The design of microwave anechoic chamber meets the requirement of performance test of urban rail transit radio equipment.