Radio wave propagation loss in the VHF to microwave region due to vehicles in tunnels

An experiment was undertaken to determine how obstacles in tunnels affect microwave propagation loss. The major emphasis of the study was on determining the propagation loss due to the following parameters: number, location, and size of vehicles, and cross-sectional shapes of tunnels. The laboratory experiments was performed using tunnel models with arched and rectangular cross sections. The dominant mode was transmitted into these tunnels from entrances. Different readings of field strength were taken along the length of the tunnels to determine the effect that vehicles can have on the propagation characteristics. The scale ratio of the tunnel dimensions to the wavelength is about 2-3. It is shown that the basic propagation loss due to vehicles in tunnels is determined mainly by the number and the size of the vehicles. Vehicle location and tunnel cross-sectional shape do not affect the propagation loss significantly