Look-ahead-radar Field Test Report Executive Summary List of Figures

Breakthroughs in the existing state of the art in the detection of abandoned mines have been successfully demonstrated in this U.S. Mine Safety and Health Administration (MSHA) project. The technical problem addressed by this breakthrough is that when an electromagnetic (EM) wave traveling at the speed of light (c) intersects natural media, such as the earth's surface or the recently cut coal face, the EM wave is slowed down and part of the wave is reflected. The part of the EM wave traveling in the slower velocity (υ) medium experiences energy loss (attenuation), intersects the second interface of the abandoned mine and returns to the detecting receiver. Often the reflected EM wave from the first interface is a factor of 1,000 (60 dB) to 10,000 (80 dB) greater than the EM wave reflected from the second interface. The first interface reflected EM wave dominates the weaker reflected wave from the second abandoned mine interface, making the second reflected wave difficult to detect. The breakthrough is the suppression of the first interface reflected EM wave at the receiver by a factor of 1,000 (60 dB) to 10,000 (80 dB) and the reception of the weaker EM wave reflected from the abandoned mine. The antenna suppression adds to the software-definable transceiver (SDT) radar predistorted waveform and real-time signal processing algorithm that enables at least 60 dB of first interface reflection suppression. Stolar Research Corporation (Stolar) has pioneered these innovations and has demonstrated a Look-Ahead-Radar (LAR) system designed around these breakthroughs in radar design. The results of field tests at these locations indicated that the technical challenges were the physical size of the radar antennas and the requirement to suppress the first air-coal interface reflected wave so that the weaker second interface reflected wave could be detected. The preliminary demonstration of the RMPA in the Sufco Coal Mine revealed that the attenuation rate was near 1 dB/ft in the coal seam, indicating to the design team that the LAR operating band frequencies needed to be in the 100-to 250-MHz range if the 20-ft void detection range was to be achieved. In this frequency range, the resonant microstrip patch antenna (RMPA) requires a patch length of 30 in. (0.75 m) for a substrate relative dielectric (ε r) constant of 4. The length decreases to 20 in. (0.5 m) for an ε r of 9. These dimensions were far too large for a cutting drum-mounted …