RF Propagation in Mines and Tunnels: Extensive measurements for vertically, horizontally, and cross-polarized signals in mines and tunnels.

This article reports measurement results on radiofrequency (RF) propagation in tunnels and mines for vertically, horizontally, and cross-polarized signals. Extensive measurements have been made in concrete tunnels, coal mines with rock dust and shotcrete, with and without conductive mesh, and hard-rock mines. The measurements include power attenuation over distances with and without line of sight (LOS) at four frequencies (455, 915, 2,450, and 5,800 MHz) that are common to underground radios, as well as swept wideband-frequency measurements from 30 MHz to 1 GHz at fixed separation distances to investigate the attenuation behavior as the waveguide cutoff frequency is approached. In addition, power loss associated with radio propagation around a 90? corner was measured for the four frequencies and two polarizations in an operational coal mine.