New techniques for the measurement of radiated emissions in a screened room for frequencies up to 200MHz.

Abstract

This thesis describes the work carried out to develop measurement techniques for the assessment of electromagnetic emissions within screened rooms for frequencies up to 200 MHz. A general introduction into the techniques presently used to assess the radiated emissions from a piece of equipment is given. Improved models to describe propagation mechanisms in a screened room in the frequency range below 30MHz are described. These are then used to develop two measurement A techniques for describing a small source in terms of its equivalent dipole moment for the frequency range up to 30 MHz. This includes techniques to identify the type of source present (i.e. magnetic or electric dipole). The propagation mechanisms in a screened room in the frequency range 30 to 200 MHz are then discussed and the effect of the cavity resonances on the measured fields is shown. A technique for reducing the Q of the resonances is presented and the results of measurements using this technique with two types of material are given. This thesis concludes that it is possible to obtain the moment of an equivalent dipole for sources below 30 MHz and that is possible to reduce the effect of resonances on measurements made at frequencies where the screened room acts as a cavity resonator. The measurements are also more repeatable because there is a reduced dependence on source and antenna positioning