An imaging system for EM emitting sources with time-domain sampling

In this paper, we propose a passive imaging system for noise source identification of digital circuit using time-domain waveform sampling. The fundamental concepts are based on optics theory. A waveform of a diffracted field on an entrance pupil is acquired by a digital oscilloscope. The phase distributions on the entrance pupil for each frequency are calculated by using Fourier transformation of the acquired waveform. Thus, an image on the focal plane is reconstructed by using Fresnel transform. The most significant advantage of the proposed method is that an image for each frequency can be obtained separately. To confirm whether the proposed method can be used for practical noise source identification, an experiment has been performed to obtain an image for an emission from personal computers. Experimental results show this fact clearly.