Recent Progress in Passive Sensing Leveraging Advanced Circuit Techniques

Passive sensing has seen considerable use as a method of detecting target distance and motion or imaging targets without requiring a cooperative transmitter. Traditionally, passive sensing has used high-power long-range illuminators of opportunity to accomplish detection at ranges on the order of hundreds of kilometers. As the proliferation of wirelessly connected devices in daily life continues, however, concerns about interference and spectrum usage have caused passive sensing to become a crucial technique to maintain the synergistic relationship between sensing and communications. Furthermore, the inherent security of passive sensing makes it a desirable choice for sensor networks. As a result, recent works have made considerable advances toward bringing passive sensing to new applications such as automotive sensing or home health monitoring. This paper reviews recent advances in passive sensing technology enabled by advanced circuit and system design techniques. New array design techniques have been shown to optimize detection ability using nonuniform linear arrays for automotive sensing, while novel passive sensing architectures have provided new techniques to extract small motions for high-sensitivity passive systems.