Korea is one of the heavily mined countries in the world. The demand for mine detection and clearance techniques has
always been high in South Korea. In support of this, a new project on ground penetrating radar (GPR) for landmine
detection has been launched in South Korea. The GPR under development is an ultra wideband sensor system that
requires high-resolution imaging of buried targets and database construction based on target signals in various ground
conditions. For initial experiments, a simple GPR has been built using a resistive vee dipole antenna and a vector
network analyzer. The GPR is scanned over a sand tank with an area of 2.5m × 2.5m and a depth of 1.5m, which is used
for target burial. During the first stage of the project, the data obtained by scanning the GPR antenna over a target are
processed to evaluate various radar signal waveforms, performance of various antennas, and other system configurations.
Based on the evaluation, an advanced GPR system will be built and used to construct the database during the second
stage of the project. A description for motivation for the GPR project, overview of the GPR project, experiment setup,
and initial experiment results are presented in this paper.
A multi-static ground-penetrating radar (GPR) has been developed to investigate the potential of multi-static inversion algorithms. The GPR consists of a linear array of six resistively-loaded vee dipoles (RVDs), a network analyzer, and a microwave switch matrix all under computer control. The antennas in the array are spaced 12cm apart so the spacing between the transmitter and the receiver pairs in the measurements are from 12cm to 96cm in 12cm increments. The size of the array is suitable for the landmine problem and scaled measurements of the buried structure problem. The RVD is chosen as an array element because it is very "clean" in that it has very little self clutter and a very low radar cross section to lessen the reflections between the ground and the antenna. The shape and the loading profile of the antenna are designed to decrease the reflection at the drive point of the antenna while increasing the forward gain. The antenna and balun are made in a module, which is mechanically reliable without significant performance degradation. The multi-static GPR operation is demonstrated on targets buried in clean sand and targets buried under the ground covered by rocks. The responses of the targets are measured by each transmitter-receiver pair. A synthetic aperture, multi-static GPR imaging algorithm is extended from conventional monostatic back-projection techniques and used to process the data. Initial images obtained from the multi-static data are clearer than those obtained from bistatic data.
The resistive vee dipole (RVD) loaded with the Wu-King profile has
many advantages for use in ground-penetrating radar (GPR)
applications. It can be designed to transmit a temporally-short
pulse to a small spot on the ground. The shape of the transmitted
pulse is simply related to the input signal, e.g., a derivative.
The RVD also has a low radar cross section. In addition, it can be
easily manufactured using a circuit board and discretely loading
it with chip resistors. One drawback of the RVD is that the input
impedance of the RVD increases significantly with decreasing
frequency and, therefore, has a high voltage standing wave ratio
(VSWR) at low frequencies, which limits the low-frequency response
of the antenna. To improve the low-frequency response, a
discretely-loaded resistive linear antenna (RLA) has been
developed, whose basic principle of operation is the same as that
of the RVD. The RLA has curved arms loaded with a modified Wu-King
profile instead of straight arms loaded with the Wu-King profile.
With an appropriate selection of the curve and the loading
profile, the low-frequency response is significantly better for
the RLA than for the RVD. The RLA has been developed using a
method of moments code. The performance of the RLA is validated
both numerically and experimentally.
A discretely loaded resistive vee dipole is designed and realized for use in pulse radiation applications, such as ground-penetrating radars. The resistive vee dipole is capable of radiating a broadband pulse whose shape is simply related to the input signal. In addition, it mostly eliminates the multiple reflections between the surface of the ground and the antenna because of its low radar cross section. Other investigators have studied the resistive vee dipoles using continuous loading. The antenna presented in this paper is printed on a circuit board and discretely loaded with off-the-shelf surface-mount chip resistors, making it easy, inexpensive to build, and mechanically stable. The characteristics of the antenna on a circuit board are measured and compared with the characteristics of the antenna in free space, which is numerically modeled using the method of moments code. The effects of the balun on the performance of the antenna are also presented.