Ground Penetrating Radar has been applied for several years to the problem of detecting both anti-personnel and anti-tank landmines. Most of the evaluation effort has focused on obtaining the end-to-end performance metrics (e.g. Pd and pfa ) of complete detection systems. This is the third in a series of papers in which we focus on the specific performance of one critical component of GPR systems: the antenna subsystem. In this paper, we examine several free-space characteristics of Planning Systems Inc. Archimedean Spiral Antennas. Specifically, we (1) investigate a spurious signal response observed with a large metal plate reflecting target, (2) determine gain and phase properties of these antennas, (3) calculate the antennas' impulse response, and (4) image several targets to validate our approach.
For several years, ground-penetrating radar (GPR) has been used to search for buried landmines. Most of the evaluation effort on complete detection systems has focused on end-to-end performance metrics (e.g., Pd and Pfa). Here, we focus on the specific performance of one critical component of GPR systems-the antennas. This is the first in a series of papers that will compare the following parameters of many different antennas: (1) the most useful bandwidths, (2) the role of polarization and polarization diversity, (3) spurious coupling effects, and (4) phase-correction considerations. This paper compares four types of Planning Systems, Inc., antennas that were developed for current and past GPR systems. These are a 5.5-in. log-spiral antenna without balun or spiral-arm terminations; 5.75-in. log-spiral antenna with tapered balun and arm termination; 5.5-in. Archimedean-spiral antenna with tapered balun, but without arm terminations; and 5.75-in. Archimedean-spiral antenna with tapered balun and arm terminations. Three main tests were performed to compare the antennas: (1) S11, to show overall matching bandwidth and to reveal discontinuities in the balun-antenna-termination structure; (2) S21, to measure undesired direct-path coupling relative to intended target scattering; and (3) S21, to show direct coupling vs. antenna spacing.
An effort is underway to develop a fused sensor system for effectively detecting both metallic and non-metallic landmines. This advanced research effort will meld two orthogonal technologies, acoustic-to-seismic coupling and ground penetrating synthetic aperture radar, into a single system with a higher probability of detection and lower false alarm rate than either technology can achieve individually. Previous testing has demonstrated that these two technologies have individually high probabilities of detection and low false alarm rates but exploit disparate phenomena to locate mines. The fact that they both produce similar data makes a high confidence mine/no mine decision possible. Future plans include a stepped development process to build a close-in detector and leveraging that experience to develop a forward-looking system capable of meeting long- term Army requirements.
This paper describes a prototype electromagnetic induction (EMI) sensor system designed specifically to measure the horizontal component of a metal target's eddy current time decay signature. Instead of creating a vertical magnetic field from a horizontal loop transmitter configuration used by most EMI metal detectors, the prototype transmitter geometry has been designed especially for creating a horizontal magneti field (HMF). One of the potential advantages of the HMF sensor is the relatively uniform magnetic field that is created over a large volume. A second potential advantage is that, compared to a conventional loop antenna, the magnetic field intensity falls off slowly with distance from the plane of the sensor. These two advantages potentially make the HMF sensor well suited for detection and classification of metal targets buried deeply in the ground (e.b., unexploded ordnance, UXO) or from a vehicle-mounted mine detector sensor. Preliminary modeling of the antenna and laboratory data from a time-domain version of the HMF sensor are presented.
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