Abstract: A transponder of a contactless data exchange system includes a unit to receive and transmit data provided with at least one first antenna loop and at least one second antenna loop in order to carry out a coupling with a reader. The transponder includes a phase shifter to shift a signal coming from the second loop by a phase shift of K*?, K being an odd integer greater than 0, to produce a phase shifted signal. The transponder includes an adder, to add a signal coming from said first loop and the phase shifted signal to produce a sum signal. The transponder also includes a unit to authorize or prevent a data transmission, depending on the sum signal. A reader of a contactless data exchange system includes a data sending/receiving unit provided with at least one antenna loop, at least one other antenna loop, and a phase shifter.

Abstract: The invention relates to a contactless data exchange system provided with a transponder comprising: a unit for receiving and transmitting data provided with at least one first antenna loop (110a, 210a) and at least one second antenna loop (110b, 210b) in order to carry out a coupling with a reader (2), means (216, 224a, 224b, 115, 116) pour authorising or preventing the data transmission according to the phase shift (??) between a first signal received by the first loop and a second signal received by the second loop.