Patent ID: 8442719

Claim:
An apparatus for authenticating communications between a user-based transponder and a vehicle-based circuit having first and second antennas, the apparatus comprising: a circuit configured and arranged to communicate a first signal between the first antenna and the transponder, therein providing vector components for the first antenna, communicate a second signal between the second antenna and the transponder, therein providing vector components for the second antenna, for each of at least two iterations, concurrently communicate same-phase signals between the respective antennas and the transponder, the same-phase signals from the respective antennas being generated using superposition factors that are based on the vector components of the antenna from which the same-phase signals are communicated, the superposition factors being different for each iteration, and authenticate the communications with the transponder by comparing summed vector components of magnetic fields of the same-phase signals for each iteration, as received at the transponder, to an error-based range for the respective vector components.