System for identifying objects equipped with an automatic transponder

Claim 1

In a system for identifying, with the aid of interrogation signals radiated from a fixed station in a directional pattern, moving objects equipped with an automatic transponder generating response signals upon receiving said interrogation signals, the improvement wherein said transponder comprises: a source of code words each consisting of a predetermined number of significant bits between a pair of framing pulses; receiving means for picking up interrogation signals including an invariant number of characteristic pulses separated by at least one variable time interval; detector means connected to said receiving means for generating an indexing signal depending upon the length of said variable time interval; transmitting means connected to said source for sending out at least one code word upon reception of each interrogation signal; programmable scrambling means inserted between said source and said transmitting means for interchanging the bits of an outgoing code word; random-access memory means containing a multiplicity of stored programs for the selective control of said scrambling means, the latter including a multiplexer with parallel signal inputs connected to said source for receiving said significant bits, address inputs connected to said memory means and an output connected to said transmitting means, said source including a mode selector with a multiplicity of output terminals respectively connected to said signal inputs; addressing means connected between said detector means and said memory means for selecting at least one of said stored programs upon reception of each interrogation signal in response to said indexing signal; and clock-controlled sequencing means connected to said addressing means for stepping same through the selected program.