Towards the Prediction of SpaceWire Radiated Emissions Employing an LVDS Signal Emulator

Abstract

The majority of the past and current ESA's, NASA's, and JAXA's science missions utilize broadly SpaceWire (SpW) Links, with Low Voltage Differential Signaling (LVDS) for the physical layer, to transfer mission data. Electromagnetic Compatibility (EMC) and Electromagnetic Interference (EMI) problems caused by harnesses' radiated emissions remain a constant open issue in every mission due to the scientific payload sensitivity. A common cause of radiated emissions from shielded cable bundles can be traced to the currents flowing on the shield of the harness. This work aims to present a complete methodology for predicting the Electric field emissions in the case of an operating SpW link, while it can be expanded to any shielded cable which utilizes LVDS. The physical and protocol layer of the link are implemented via a developed LVDS Signal emulator, handling both the characteristics of the signals at the outputs of the LVDS line drivers and the effects of their transmission across the link along with the termination scheme, in order to calculate the common mode current flowing on the shield. The radiated emissions can then be estimated considering the ground material and a detailed harness topology, employing traveling wave antenna theory. The validity of this approach is assessed by comparing the predictions with actual link radiated emissions measurements. Simulation results are in good agreement with the measurements, rendering this methodology a fast tactic for the pre-compliance procedure for the early design stage of the science space mission.