Landmine locating system

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
1 represents a landmine detecting system 100.
An area of the ground 102 is systematically scanned by a ground-penetrating radar unit 104.
A resonant microstrip patch antenna (RMPA) sensor 106 is moved in a search pattern over area 102.
A sonic position-locating device 108 has a probe 110 that can determine where the RMPA sensor 106 is stationed.
A display screen 112 presents a graphical user interface (GUI) which represents the area 102 and any buried objects in the area that have been detected and located.
Such information is also preferably relayed to a platoon leader's console 114.
The RPMA sensor 106 is part of a ground-penetrating radar and is driven by a three-port directional coupler.
A reflected-wave output port is buffered by a wideband isolation amplifier and a reflected-wave sample is analyzed to extract measured values of the real and imaginary parts of the load impedance, e.
g.
, the driving point impedance of RMPA.
Each such port will vary in a predictable way according to how deeply an object is buried in the soil.
Calibration tables can be empirically derived.
Reflections also occur at the interfaces of homogeneous layers of material in the soil.
The reflected-wave signals are prevented from adversely affecting transmitted-signal sampling by putting another wideband isolation amplifier in front of the input port of the directional coupler.
A suppressed-carrier version of the transmitted signal is mixed with the reflected-wave sample, and the carrier is removed.
Several stages of filtering result in a DC output that corresponds to the values of the real and imaginary parts of the load impedance.
The suppressed-carrier version of the transmitted signal is phase shifted 0.
degree.
or 90.
degree.
to select which part is to be measured at any one instant.
The landmine detecting system 100 is typically calibrated by vertically sweeping the RMPA antenna sensor head 106 up a foot above the soil and then back down to the soil surface while collecting a number of readings at known elevations