Measurement and Simulation for the Properties of Small Anechoic Chamber
| Autor: | Jia-MIng Ji, 紀家銘 |
|---|---|
| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 In this study, the properties of EMC/EMI and antenna measurement of an anechoic chamber were established by using a simulation program and a data-calibration technique. In the simulation of electromagnetic (EM) characteristics of an EMC chamber, the image theory, Snell’s law, and a ray-tracing method were used to establish a simulator, which was written using Matlab. The simulator can deal with the normalized site attenuation (NSA), normalized site transmission loss (NSTL), field uniformity (FU), and reflectivity level (RL) of a chamber. For calibration purposes, data measured in the NYUST EMC chamber were compared with those collected in MiTAC’s and SPORTON’s chambers, both in EMC and antenna measurements. The NYUST anechoic chamber can be used for both EMC/EMI tests and antenna measurements. For EMC/EMI tests, some techniques were used to suppress ambient EM noises in the chamber. An EMC site source was developed for conducting the correlation test between a small fully anechoic chamber and a standard 10-m semi-anechoic chamber. A correction factor was established for the NYUST anechoic chamber. As a result of taking the correction factor into account, the measurement became more accurate and reliable than before. For antenna measurements, a double ridge horn was developed for conducting the correlation test between a small fully anechoic chamber and a standard fully anechoic chamber. A correction factor was computed for the NYUST anechoic chamber. The correction factor was hence used to improve the antenna-pattern measurement performed in this chamber. NSAs of AIDC’s semi anechoic chamber and NSTLs of USI’s fully anechoic chamber were measured and compared with simulation results. Both the simulated and measured NSAs of AIDC’s chamber were observed to comply with the ANSI C63.4 directive except for the simulated vertical-polarization part below 40 MHz. It was also found that the second-order reflected rays should not be omitted in the simulation of NSAs if the return-loss level of the RF absorber is less than 20 dB for a 9-6-6 chamber. Furthermore, both the simulated and measured NSTLs of USI’s chamber agree with the theoretical values computed using the Friis transmission equation. |
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