Reconstruction of Equivalent Source Using a Single Component of the Near Field Measurement for Predicting Far Field Emissions

Near field measurement has been widely used as an efficient and effective method for EMC diagnoses purpose in PCB designs. The far-field radiated emission level of an electronic device, in accordance with the EMC test requirements, can be evaluated based on the measured near field emission level of that device. To predict the far field emission, an equivalent current source from near-field measurement is first reconstructed based on the Huygens’ equivalence principle; the far field radiation pattern can then be calculated from the equivalent current source. This Huygens’ equivalence principle typically requires the measurements of at least two tangential electric and/or magnetic field on the measurement plane of the device. When the dimension of the device is smaller than the wavelength of the concerned frequencies, it can be considered as electrically small, especially in the case of an IC chip or a PCB. The equivalent current source can easily be reconstructed by using only one single field component of the near field measurement. By employing the Uniqueness Theory, the far field solution exists with the knowledge such boundary values, which can be evaluated from the equivalent current source. In the project, we investigate a novel approach in obtaining a planner equivalent current source to that of an electrically small PCB, using only the normal components of the magnetic field perpendicular to the surface of the PCB. This study will establish a simple and yet novel approach to estimate the far field radiation pattern, for EMC diagnostic and redesign of PCBs.