Method and apparatus for remote detection of radio-frequency devices

A method for detecting the presence of a radio device, comprising:

• transmitting a complex radio frequency stimulus into a target area;
• processing nonlinear reflection signals received from the target area to obtain a response measurement;
• and
• comparing the response measurement to a pre-determined filter response profile to detect the presence of a radio device having a corresponding filter response characteristic;
• wherein transmitting a complex radio frequency stimulus comprises transmitting a first component at a first frequency and transmitting a modulated second component at a second frequency, the modulated second component having a modulation bandwidth, wherein the first frequency, the second frequency, and the modulation bandwidth are selected so that a third-order intermodulation product produced by the first and second components has a bandwidth that substantially overlaps a band-edge of a predicted device response;
• and wherein the processed nonlinear reflection signals correspond to the third-order intermodulation product of the first and second component.

An apparatus for detecting the presence of a radio device, comprising:

• a transmitter section configured to transmit a complex radio frequency stimulus into a target area, the complex radio frequency stimulus comprising a first component at a first frequency and a second component swept between a second and third frequency, wherein the first, second and third frequencies are selected so that third-order intermodulation products of the first and second components traverse a band-edge of a predicted device response;
• a receiver section configured to receive nonlinear reflection signals from the target area wherein the nonlinear reflection signals correspond to the third-order intermodulation products;
• and
• a signal processing section configured to process the received signals to obtain a response measurement and to compare the response measurement to a pre-determined filter response profile to detect the presence of a radio device having a corresponding filter response characteristic, wherein the signal processing section is configured to obtain a response measurement comprising a first amplitude value corresponding to at least one frequency below a band-edge of a predicted device response and a second amplitude value corresponding to at least one frequency above said band-edge, and wherein the signal processing section is further configured to compare the difference between the first amplitude value and the second amplitude value to a pre-determined threshold to detect the presence of the radio device.

An apparatus for detecting the presence of a radio device, comprising:

• a transmitter section configured to transmit a complex radio frequency stimulus into a target area;
• a receiver section configured to receive nonlinear reflection signals from the target area;
• and
• a signal processing section configured to process the received signals to obtain a response measurement and to compare the response measurement to a pre-determined filter response profile to detect the presence of a radio device having a corresponding filter response characteristic;
• wherein the transmitter section is configured to transmit a complex radio frequency stimulus by transmitting a first component at a first frequency and transmitting a modulated second component at a second frequency, the modulated second component having a modulation bandwidth, wherein the first frequency, the second frequency, and the modulation bandwidth are selected so that a third-order intermodulation product produced by the first and second components has a bandwidth that substantially overlaps a band-edge of a predicted device response;
• and wherein the nonlinear reflection signals correspond to the third-order intermodulation product of the first and second component.