System Locates Buried Objects Marked by Electromagnetic Tags

A relatively inexpensive, lightweight, durable, easy-to-operate radio-frequency (RF) instrument has been developed, along with special electromagnetic tags, for use in detecting buried objects to which the tags are attached. Each tag comprises a dipole antenna (basically, two collinear straight wires) with a passive, electrically nonlinear load between them. By virtue of the nonlinearity of the load, the antenna reradiates harmonics and/or mixer product(s) of one or more RF signal( s) transmitted by the instrument. The instrument detects one or more of the harmonics and/or mixer products and executes a time-of-arrival measurement procedure to locate the tag. The instrument is especially well suited for locating buried pipelines marked with such tags.