Application of Emission Source Microscopy Technique to EMI Source Localization above 5 GHz

Abstract - This paper presents the utilization of the emission source microscopy (ESM) technique to localize active sources of radiation on a PCB. For complex and large systems with multiple sources, localizing the sources of radiation often proves difficult. Near-field scanning provides limited information about the components contributing to far-field radiation. Two-dimensional synthetic aperture radar, a well-known technique used to diagnose and align phase array antennas, is adapted as emission source microscopy and utilized here for this alternative application. This paper presents the source localization methodology, along with simulation and measurement results. The results show that the proposed method can detect multiple active sources on a complex PCB. Keywords — source localization; EMI; emission source microscopy; SAR; near-field scanning. I. I NTRODUCTION Near-field electromagnetic scanning often is used for root cause diagnosis by determining near-field radiation patterns and coupling mechanisms. Near-field scanning may provide information about the surface current, tangential fields and the reactive near-field distribution on the device under test (DUT). The near-field contains both evanescent and propagating fields. The evanescent waves are dominant, which may lead to the misinterpretation of the dominant sources contributing to the far-field. In practice, however, engineers mainly are concerned about only the sources of electromagnetic interference (EMI) contributing to far-field radiation. To identify these sources, engineers must depend upon their experience or trial and error. Another limitation of near-field scanning is that the probe may not be able to access all locations near the PCB due to the complex geometry and high component density. This leads to the incorrect measurement of fields at different vertical distances from the PCB. One advantage of near-field scanning is that it can achieve better resolution depending upon the scanning step and the probe size. To overcome the limitations of near-field scanning in locating EMI radiation sources, the emission source microscopy presented in this paper can be used to determine the sources of far-field radiation. In the literature, the investigators in [1] discussed a similar idea for detecting faulty antennas in antenna arrays. They performed two phase-synchronized near-field measurements before applying the synthetic aperture radar (SAR) algorithm to detect faulty antennas. SAR techniques are used mainly for antenna diagnostics and antenna pattern measurements [2]. Such techniques also have been used for microwave imaging to detect concealed objects and structural defects [3]-[5]. Standard SAR methods use signals reflected from a target and received by a scanning antenna to reconstruct the target’s image. The method proposed in this paper uses a 2D ESM algorithm based on the SAR technique to detect active sources of radiation on a complex PCB. The fields from the active radiation sources, along with the amplitude and phase, are measured on a planar surface away from the DUT. The ESM algorithm is applied to propagate the fields back to the source plane and to localize the source of radiation. The method is presented using an analytical formulation and validated using both full-wave simulations and measurements. II. EMISSION SOURCE MICROSCOPY ALGORITHM