Method and apparatus for interrogating and identifying fixed or moving targets
First Claim
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1. An object identification system comprising:
- a transponder mounted on an object to be identified;
means for interrogating said transponder with a beam of electromagnetic wave energy;
said transponder including at least one non-linear device having an conductive state and a non-conductive state and reradiating a signal back to the means for interrogating in response to impingement upon said device of energy from the means for interrogating, the frequency of said signal being harmonically related to the frequency of said wave energy;
means for modulating the harmonic signal reradiated back towards the interrogating means to identify uniquely the object on which said interrogating means is mounted, said modulating means includingmeans for generating a repetitive m-bit identification code;
means responsive to each bit of said m-bit code for generating an n-bit pseudo-random code sequence for said each bit corresponding to the instantaneous logical value and relative position of that bit of said identification code; and
means responsive to said pseudo-random code sequence generating means for selectively biasing said at least one non-linear device to either one or the other of said two states m ×
n times for each occurrence of said m-bit identification code.
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Abstract
Hijacked vehicles, or the like, are identified by illuminating a transpon mounted to the vehicle by a beam of microwave energy, e.g., from a helicopter flying over the traffic. The transponder includes non-linear diodes which reradiate a signal back towards the helicopter. Means are disclosed for modulating the return signal with a 16-bit identification code, each bit of which is transmitted as a 31-bit pseudo-random code.
30 Citations
10 Claims
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1. An object identification system comprising:
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a transponder mounted on an object to be identified; means for interrogating said transponder with a beam of electromagnetic wave energy; said transponder including at least one non-linear device having an conductive state and a non-conductive state and reradiating a signal back to the means for interrogating in response to impingement upon said device of energy from the means for interrogating, the frequency of said signal being harmonically related to the frequency of said wave energy; means for modulating the harmonic signal reradiated back towards the interrogating means to identify uniquely the object on which said interrogating means is mounted, said modulating means including means for generating a repetitive m-bit identification code; means responsive to each bit of said m-bit code for generating an n-bit pseudo-random code sequence for said each bit corresponding to the instantaneous logical value and relative position of that bit of said identification code; and means responsive to said pseudo-random code sequence generating means for selectively biasing said at least one non-linear device to either one or the other of said two states m ×
n times for each occurrence of said m-bit identification code. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification