Passive Multistatic Wireless Sensing Based on Discrete LNA/Mixer Co-Optimization and Fast-Startup Baseband Amplifier

Passive radar has gained considerable interest as a mechanism of characterizing small motions using ambient electromagnetic (EM) energy. Compared to traditional Doppler radar, passive radar offers a means of motion detection leveraging existing signals such as Wi-Fi or Bluetooth to reduce crowding in the EM spectrum. Previous works have demonstrated an ability to detect periodic motions using passive radar but relied on bulky commercial building blocks that increase both size and power consumption of the overall device. Amplification of the low-frequency signals is often accomplished using baseband amplifiers with high-pass behavior, resulting in long startup times when detecting low-frequency motions. In this work, a board-level passive radar operating in the 5-GHz Wi-Fi band is presented as a method of detecting small motions created by human motion. The proposed system offers a compact, efficient method of detecting the Doppler information of a target. A fast-startup baseband amplifier is used as a method of quickly reaching the desired operating point, while keeping cost and complexity low. The radar is tested both in a controlled and experimental setting to verify its effectiveness in detecting small-amplitude motions. The results demonstrate that passive radar offers a low-power solution to detecting motion using ambient signals.