A DIRECTION FINDING OF CONDUCTED INTERFERENCE USING THE COUPLED TRANSMISSION LINES

As a method of evaluating the direction of arrival of conducted interference propagating along a transmission line, a measurement method using coupled transmission lines is investigated. The principle of measurement is the direction selectivity of the coupled transmission lines consisting of two parallel lines. The direction of propagation of the conductive noise is sensed from the difference of the response voltages at the two ends of the coupled transmission line. In the present experiment, a strip line with a characteristic impedance of 50 ohms made of a two-sided substrate of length 12 cm and width 3 cm is used as the coupled line. With this test transmission line, the coupling characteristics of the transmission lines are experimentally confirmed based on a homogeneous transmission line model. With a standard power supply cord as the line under test, the response voltage for the conducted electromagnetic interference generated from a small generator is measured. It is confirmed that the response voltage of the coupled line depends on the direction of propagation of the transient voltage propagating along the transmission line. Hence, it is shown that detection of the direction of propagation of the conducted interference can be carried out easily. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(7): 23–31, 1997