Study on the Characteristics of RF-EMI suppressing devices

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In recent years, personal wireless systems such as mobile radio and wireless LANs have been developed very rapidly. On the other hand, the operating frequency of IT equipment and other devices has been increased up to the GHz frequency band to achieve greater performance. Hence strong anxieties have been raised about the possible interference with wireless systems caused by electromagnetic disturbances emitted from such devices. To control interference, IEC/CISPR has been studying the limits and measurement methods of the radiated emissions above 1 GHz. To comply with the regulations, a variety of EMI suppressing devices such as ferrite cores are used in electronic equipment. But, design methods have not been established for such EMI suppressing devices.Thus, this research project theoretically and experimentally investigated the noise reduction capability of the EMI suppressing devices and the related measurement methods above 1 GHz.1.Measurement method of wideband radiated emissionsRadiated disturbances from electronic equipment are requested to be measured with antennas in accordance with the relevant regulations. Hence EMI measuring antennas are one of the most important equipment in the measurement system. Therefore, accurate calibration method has been developed in this project for characterizing various wide band EMI antennas.2.Characteristics of EMI ferrite coresEMI ferrite cores are commonly used for the purpose of reducing the disturbance current flowing on the power lines of electric equipment. However, reduction mechanism and characteristics of the ferrite cores have not been fully investigated so far. Accordingly, this project investigated a new method for measuring the effectiveness of EMI ferrite cores in reducing the disturbance, and then tried to develop the design method to yield suitable materials and structures of ferrite cores.