A New Method for Determining the Emission Characteristics of an Unknown Interference Source

There has been considerable interest in developing a practical method to determine quantitatively the ra­ diation characteristics of unintentional electromagne­ tic emitters [1,2,3]. The objective of this paper is to describe such a method developed recently at the National Bureau of Standards, Boulder, Colorado. Basically, an unintentional leakage source is con­ sidered to be electrically small, and may be charac­ terized by three equivalent orthogonal electric and magnetic dipole moments as shown in figure 1. When an unknown source object is placed at the center of a transverse electromagnetic (TEM) cell shown in figure 2 , its radiated energy couples into the fundamental waveguide mode and propagates toward the two output ports of the TEM cell. With a hybrid junction inserted into a loop connecting the cell output ports such as that given in figure 3, one is able to measure the sum and difference powers and the relative phase between the sum and difference outputs. Systematic measure­ ments of these powers and phases at six different source object positions, based on a wel 1-developed theory, are sufficient to determine the amplitude and phases of the unknown component dipole moments, from which the detailed free-space radiation pattern of the unknown source and the total radiated power can be de­ termined. Results of an experiment using a spherical dipole radiator are given to illustrate the theory and measurement procedure. ENEIECTWC raUlfHEKT w m m