A New Generation Method of Rotating-em Field for Rf Radiated Immunity/susceptibility Test

1. Introduction Several kinds of RF (radio frequency) radiated immunity/susceptibility test methods have been proposed, and put to practical use. The test methods using transverse electromagnetic (TEM) devices such as TEM cell and GTEM cell have already been standardized. By using these methods, the immunity/susceptibility characteristics to the electromagnetic (EM) field in a fixed direction or of a constant polarization can be obtained. On the other hand, an immunity/susceptibility test method using EM field with slowly rotating polarization (rotating-EM field) has been proposed in reference [1]. The rotating-EM field differs from the circular-polarization field, that is, the polarization plane of the field rotates in a much lower frequency than the carrier frequency. By using the rotating-EM field in the immu-nity/susceptibility measurement, the radiated immunity/susceptibility characteristics of equipment under test (EUT) for various polarizations can be obtained easily in a short time. Moreover, by using a turntable together, the immunity/susceptibility characteristics for incident angles of the EM field can be automatically measured at the same time. However, there are a few weak points in the system in [1]; some synchronous signal generators (SGs) is necessary to generate the rotating-EM field accurately and the generating system is complicated. Therefore, the immunity/susceptibility measurements to various frequencies in a wide band are difficult in the method. In this study, a new system for generating the rotating-EM field is proposed. The new generating system is composed of a microprocessor, some voltage-variable attenuators (VVAs), and some bi-phase switches, and only one SG is necessary for the system to generate the rotating-EM field. By using this system, it is expected that the rotating-EM field of an arbitrary polarization in a wide-frequency band can be generated more easily. The principle of the proposing system is clarified. Moreover, the rotating-EM field is generated in an anechoic chamber and then the basic characteristics of the resultant field are examined. In addition, the