The curvature of tunnels introduces an extra loss in the wave propagation. A simulation and measurement study are performed on the straight and the curved tunnels to investigate the extra loss in the curved tunnels in comparison with the straight tunnels at a frequency of 2.4 GHz. This study suggests the existence of two wave propagation mechanisms in the curved tunnel; enhanced waveguiding mechanism induced by rich multipath
components from the curved tunnels and degraded waveguiding mechanism due to the blockage from the curved tunnel walls. For efficient radio planning, a new propagation model with curvature dependent break point is proposed. The proposed break point indicates the end of the enhanced waveguiding mechanism and
the beginning of the degraded waveguiding mechanism. A two-slope radio wave propagation model is then proposed for radio communications inside curved tunnels by using the determined break point, with performance evaluation.
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This research is supported by the Core Funding of A*STAR, Singapore.