Thesis (M.Eng.) - Asian Institute of Technology, 1997

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering.

According to international standards, EMC measurement has to be performed in an open area test site or its equivalent test site, such as a semi-anechoic chamber. To validate a test site, site attenuation test must be performed in that particular site. If the measured normalized site attenuation is within the 4dB range of the standard value, the site can be considered as qualified. To predict the performance of a semi-anechoic chamber before its construction and to find out the reason which may lead measured site attenuation exceed the limitation, a theoretical model must be considered. The existing model using ray tracing theory generally models the measurement antennas as a theoretical half-wave dipole antennas. This antenna model is appropriate for some EMC measurement antennas, such as tunable dipole and biconical antenna. However, when this antenna model is used to represent the measured results made with log-periodic dipole antennas, significant discrepancy appears (Gavenda, 1993). In this study, a general chamber model using ray tracing theory is developed. Since the model allows the true radiation pattern of different antennas to be included, it can be used for all types of EMC antennas. Based on the developed chamber model, the effect of log-periodic antenna has been studied and the method to eliminate the error caused by log-periodic antenna are also proposed.