Transmission line and electromagnetic model of the tubular wave coupler

This paper investigates the injection of RF energy onto wiring harness using a tubular wave coupler (TWC). In particular, a transmission line (TL) model of a commercial TWC mounted in the calibration fixture provided by the manufacturer is developed. The proposed model of the calibration setup provides accurate prediction of the measured insertion loss up to 2 GHz. Measurement data and outcomes of three-dimensional electromagnetic simulation of the TWC are used to obtain estimates of some of the involved model parameters, whose direct evaluation is not possible due to partial knowledge of the geometrical/electrical characteristics on the one side, and nonuniform distribution of current and voltage on the TWC cross section on the other. The proposed TL model is used to explain the fundamental phenomena responsible for RF-energy transfer through the TWC. Particularly, it is shown that, differently from bulk current injection probes where inductive coupling is the dominant phenomenon, injection through the TWC involves both inductive and capacitive coupling. This determines a certain amount of directivity of the injection device, and is expected to play a role in RF injection onto complex cable bundles.