Surveillance apparatus and method for the detection of radio receivers
First Claim
1. An electromagnetic surveillance system for detecting the presence of receivers having non-linear demodulation elements in the input channels thereof within a predetermined surveillance region comprising:
- signal generation means for supplying an electrical signal including signal components at a first and second predetermined frequency, said signal generation means including means for modulating said electrical signal;
means responsive to said electrical signal supplied by said signal generation means for establishing an electromagnetic surveillance field within a predetermined surveillance region, said electromagnetic surveillance field having signal components at said first and second predetermined frequencies;
means for detecting electromagnetic waves at frequencies which correspond to at least one intermodulation frequency of said first and second predetermined frequencies, said detecting means including means for excluding signals at said first and said predetermined frequencies; and
ranging means responsive to said means for detecting electromagnetic waves for determining the distance from said electromagnetic surveillance system to a receiver unit causing said electromagnetic waves at said intermodulation frequencies.
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Accused Products
Abstract
Method and apparatus for the detection of a target receiver unit such as an enemy radar or radio receiver is disclosed. The surveillance system of this invention includes a transmitter unit coupled to an antenna to establish an electromagnetic surveillance field that includes signal components at two predetermined surveillance frequencies. When a target receiver is located within the surveillance field, the target receiver produces a second electromagnetic field having signal components at the intermodulation products of the surveillance field signal components due to a nonlinear mixing process that occurs within the target receiver. Signal components at predetermined intermodulation frequencies are detected by a receiver circuit within the surveillance system that has a passband excluding signal components at the two predetermined surveillance frequencies. Since signals at the intermodulation frequencies are present only when a target receiver is presents detection is accomplished without the necessity of distinguishing between signals reflected from a target receiver and signals reflected from other obstacles.
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Citations
10 Claims
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1. An electromagnetic surveillance system for detecting the presence of receivers having non-linear demodulation elements in the input channels thereof within a predetermined surveillance region comprising:
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signal generation means for supplying an electrical signal including signal components at a first and second predetermined frequency, said signal generation means including means for modulating said electrical signal; means responsive to said electrical signal supplied by said signal generation means for establishing an electromagnetic surveillance field within a predetermined surveillance region, said electromagnetic surveillance field having signal components at said first and second predetermined frequencies; means for detecting electromagnetic waves at frequencies which correspond to at least one intermodulation frequency of said first and second predetermined frequencies, said detecting means including means for excluding signals at said first and said predetermined frequencies; and ranging means responsive to said means for detecting electromagnetic waves for determining the distance from said electromagnetic surveillance system to a receiver unit causing said electromagnetic waves at said intermodulation frequencies. - View Dependent Claims (2, 3, 4)
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5. An electromagnetic surveillance system for determining the presence of a remote receiver unit having a non-linear mixer stage comprising:
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a transmitter unit for supplying an electrical signal including a signal component at a first predetermined frequency, f1, and a signal component at a second predetermined frequency, f2, said transmitter unit including means for modulating said supplied signal; a receiver unit including means for indicating the reception of an electrical signal at at least one of the frequencies mf1 ±
nf2 where n and m equal ±
1, ±
2, . . . and m+n equal an odd integer;an antenna responsive to said electrical signal supplied by said transmitter unit for supplying an electromagnetic surveillance pattern, said antenna further responsive to an impinging electromagnetic wave for supplying an electrical signal at the frequency components of said impinging electromagnetic wave; means for coupling said electrical signals supplied by said antenna to said receiver unit; and a ranging circuit responsive to the signal supplied by said receiver circuit for determining the distance between said surveillance system and said remote receiver unit. - View Dependent Claims (6, 7)
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8. A method for detecting the presence of receiver unit comprising the steps of:
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generating an electrical signal including signal components at a first and second predetermined frequency, modulating said electrical signal including said signal components at said first and second predetermined frequencies to supply a modulated electrical signal; transmitting a modulated electromagnetic wave representative of said modulated electrical signal; and detecting the presence of electromagnetic waves at at least one frequency corresponding to an intermodulation product of said first and second predetermined frequencies, said step of detecting including the step of deriving signals proportional to the modulation of the detected electromagnetic waves to determine the distance to that receiver unit producing said electromagnetic waves including said intermodulation product. - View Dependent Claims (9, 10)
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Specification