Abstract: An apparatus and method for detecting and locating hidden objects employs a symmetrical array of five directional antennas, including a central transmit antenna and a pair of receive antennas at each side of the transmit antenna, respectively. All of the antennas are pointed in the same general direction toward an object field of interest. The transmit antenna radiates a beam of high-frequency electromagnetic energy, and the receive antennas receive high-frequency electromagnetic energy returned by hidden objects. Each pair of receive antennas has an associated phase detector, the output of which represents the phase difference between receive antenna signals corresponding to the received electromagnetic energy. A circuit determines when the outputs of the phase detectors represent predetermined phase differences and operates indicator devices.

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.