Measurement Procedure for Cyclostationary Characterization of PCB Radiated Emissions

Measurement techniques of stochastic electromagnetic emissions in the near-field of the PCB can be realized in time domain by sensing of the transient emissions with a scanning system equipped by two probes and real time digital oscilloscope. Radiated electromagnetic interference originating from digital circuitry exhibits properties of cyclostationarity caused by random bit sequence travelling along the line over the surface of the PCB. The relation between the source signal and the signals measured by the near-field probe at each scanning point was modelled by an impulse response describing linear transformation of the source signal. In this paper evaluation procedure for obtaining impulse responses in all scanning points over the PCB by appropriate cyclic averaging of stochastic signals simultaneously measured by the reference and scanning probes is presented. Obtained impulse responses can be used for computer aid prediction of the spatial-time evolution of the cyclostationary characteristics in the environment surrounding the PCB and directly on the surface of the PCB. Verification of the described measurement procedure was implemented by comparison of the calculated autocovariance function based on impulse response and the same autocovariance function evaluated from the measurement results for digital data sequence with different cyclostationary properties.