Modeling RF propagation in tunnels

As mandated by the 2006 Mine Improvement and New Emergency Response (MINER) Act, many underground coal mines have installed UHF radio systems to provide communications between personnel on the surface and underground. In an effort to better understand UHF signal propagation in tunnel environments, we made radio signal attenuation measurements in concrete tunnels at frequencies of 455 MHz, 915 MHz, 2.45 GHz, and 5.8 GHz. In this paper, a ray tracing method is used to model the channel. Although the tunnel has an arched roof, the model describes the propagation behavior very well using a rectangular tunnel with the same width. The measured data verify the ability of the ray tracing model to predict radio frequency propagation at all the four frequencies. In addition, the propagation constants for the different frequencies are investigated and shown to be consistent with the measured values.