Abstract: An apparatus for detecting an object, including a transmitter and an antenna that receives a signal from the transmitter, radiates a transmitted beam of electromagnetic energy, and receives a reflected beam of electromagnetic energy, the reflected beam being a reflection of the transmitted beam when the transmitted beam is reflected from an object. The apparatus further includes a phase detector in communication with the antenna that detects a phase difference between the transmitted beam and the reflected beam, and that produces an output based on the phase difference, and a voltage meter that receives the output and produces a voltage reading.

Abstract: Continuous-wave radiation is used to detect a target hidden behind a surface. In an embodiment, a transmitter directs a beam of continuous-wave microwave radiation from a transmitting location, and reflected radiation from the target is received at first and second receiving locations closer to the surface than the transmitting location. The transmitting and receiving locations have spatial relationships such that the phase of reflected radiation received at one receiving location is in quadrature with the phase of reflected radiation received at the other receiving location. In an embodiment, direct transmitted radiation is received at the receiving locations in quadrature.