Patent ID: 8131239

Claim:
A method for detecting the presence of a radio device, comprising: transmitting a complex radio frequency stimulus into a target area by transmitting a first component at a first frequency and sweeping a second component 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; processing nonlinear reflection signals received from the target area to obtain a response measurement, wherein the processed nonlinear reflection signals correspond to the third-order intermodulation products and wherein the response measurement comprises 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 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 by comparing the difference between the first amplitude value and the second amplitude value to a pre-determined threshold.