Performance Evaluation Of A 5-meter Anechoic Chamber

It is quite expensive to build an anechoic chamber, and with an integrated consideration of cost and performance, it is necessary to evaluate its performance before the construction. The paper adopts the theories of electromagnetic propagation, wave reflection to discuss the performance evaluation method of a new-type electromagnetic compatibility (EMC) measurement environment — a 5-meter anechoic chamber in the entire work frequency bands (30MHz ~1000MHz) with the focus of its key parameter - normalized site attenuation (NSA) evaluations and analyses with the application of Ray Tracing Method and FDTD method at the corresponding frequency bands.It applies ray tracing (RT) method combined with the discrete frequency sweeping method of tunable dipole antenna in the frequency bands of 300 MHz~ 1000MHz. EM waves are regarded as a serial of radial bunches and inner walls and the ceiling of the chamber are discrete with uniform size of base size of the hybrid EM absorbers. Reflection number for each ray has been added to 3 compared to the traditional count of 2, and a new matrix solution to combined equations of rays' tracks and inside-walls to obtain the reflection points has been adopted which greatly enhanced the operation efficiency. Electric fields strengths are overlapped in vector at each discrete unit of the inner wall and then it obtains the electric field distributions of each wall with a radiation source of doublet dipole antenna which determines basically the main reflection areas of each wall, and then the paper further evaluated the normalized-site-attenuation (NSA) value. The result shows that when the antenna is in both vertical and horizontal polarization, the prediction values comply with 4dB Rule of the theoretical values obtained from the open area test site (OATS). The thesis also offers a layout of hybrid EM absorbers with a coverage ratio less than 80%.In frequency-bands of 30MHz~300MHz, finite dimension time-domain (FDTD) method is used to carry out the evaluation. At the foundation of studying the FDTD theory, the paper models and simulates the process of EM wave propagation and its transmission and receiving in the antenna with the application of matrix processing software. The simulation procedure of 3-dimension symmetric dipole antenna has been make up and then the paper discusses detailed the simulation construction of the antenna and prompt source. The indoor field strength distributions are calculated via simulating the reflection of conductor board and further it discusses the NSA evaluation of a chamber equipped with Ferrite titles.Seen form performance evaluation curves of NSA, in low section of low frequency bands, about 30MHz~100MH, the difference between evaluation and theoretical ones is larger than 4 dB while the evaluation agrees with 4dB Rule of the theoretical values in other segments of the lowfrequency bands and it is evident to observe its tendency of being close to acceptable segment with the rise of the frequency. The result implies that the model of the dipole antenna agrees with the reality at most of the bands with some disparity at low segment, so it should be improved or model log periodic dipole antenna (LPDA) in FDTD.Compared with the two popular types, 3-meter chamber and 10-meter chamber, the 5-meter chamber has advantages in the price/performance ratio of the chamber foundation, testing field performance and so on, therefore it stands for direction for chambers development The evaluation methods discussed in the thesis are significative to some extent to the construction of the 5-meter anechoic chamber and improvement of its practical capability.