Abstract: A vehicle anti-theft system in the form of a mechanically interengagable electronic key and lock includes stored key and vehicle identifiers in both the key and in the lock. A random number is generated in the lock each time the vehicle ignition switch is closed and that random number is used to encode one of the identifiers for transmission to the key. The key uses the corresponding stored identifier to recover the random number. The other stored identifier is then encoded using the recovered random number and the encoded other identifier is returned to the lock. The lock uses the generated random number to recover the second identifier for comparison to its stored value. If the comparison fails, vehicle operation is prevented. The system may effect several trials, each using a new random number before refusing further attempts. The lock electronics is preferably disposed in the vehicle fuel tank and controls operation of the vehicle fuel pump.

Abstract: A method for inhibiting responses by transponders to interrogation signals originating in the side lobes of an interrogating radar of a secondary radar system. The interrogating radar first transmits a reference signal with the highest power level of the reference signal being directed into a zone of interest to the interrogating radar. The interrogating radar then transmits a control signal having a higher power level than the reference signal in all regions of space except within the zone of interest. The control signal is of substantially longer duration than the reference signal. A transponder receives, detects and measures the peak amplitude of the reference signal and establishes a minimum trigger level (MTL) at a predetermined level below the reference signal peak. The control signal is received, detected and integrated. The peak amplitude of the integrated control signal is compared with the MTL.