Estimation of the Operating Range of Automotive Key Fobs during a Radiated Emissions Test under a Low Frequency Band

This paper presents a method of estimating the available range of mutual positions of magnetically coupled circuits performing the function of a contactless communication interface. The criterion of correct operation is the level of radiated emission; the value of which depends on the spatial orientation of the cooperating inductors. The sources of the generated harmonic disturbances, which are the nonlinearities of the output stage of the transmitter and the input circuits of the receiver, have been identified. On this basis, a peripheral model was created that allows prediction of the level of disturbances in a given position. The emission measurement in the ALSE chamber in a low frequency band of up to 1.7MHz was used as the verification method. The correctness of the proposed method was confirmed by the evaluation of the interface of the immobilizer commonly used in automotive vehicles.