Electromagnetic Wave Sensor for Proximity Target Detection Under Radio and Radar Coexistence at 2.4-GHz ISM Band

Abstract

This paper presents an electromagnetic (EM) wave sensor that detects an indoor target located at near field region under the coexistence of a seamless indoor WiFi radio link at 2.4 GHz. In a radar calibration mode, the EM sensor utilizes an electromagnetic wave balance state where a transmit leakage to a receive path is balanced out by an internal control signal. After the calibration, any residual transmit leakage power together with ambient WiFi signal power sets a level of reference detection threshold power around 10 nW (-50 dBm). In a target detection, the presence of a target breaks the EM wave balance state and the EM wave sensor produces a detection output power governed by a quartic radar equation. At the presence of a flat round metal target with radius = 5 cm, the detected power level ranges from 10 nW to 1 µW (-30 dBm) when the sensing distance (r) decreases from the edge of a radiative near field (r = λ = 12.5 cm) to the reactive near field (r = λ/2π = 2 cm), well matched with theoretical estimations. Under the 2.4-GHz radar-radio joint environment, the sensor desensitizes any target in a far field region (r > λ) by the surrounding radio noises, making it suitable for a proximity sensor with aiming applications of cost-effective noncontact wakeup sensors including computer/laptop monitor wakeup sensors, gesture or security motion sensors, or IoT sensors wakeup stimulators.