Research And Design Of Antennas To Realize Efficient Radio Coverage In Tunnel Environments

The environments in confined spaces such as tunnels and mines are very complex and changeable.When the radio wave is propagates in these confined spaces,it will be affected by the reflection and diffraction of the tunnel wall,thus forming a complex electromagnetic environment.In such a confined space,it is difficult to provide good communication quality,and may even lead to security incidents without efficient radio coverage.At present,traditional antennas such as Yagi antennas and helical antennas are mostly used as tunnel antennas.The characteristics of the confined space are not considered in the design process of these antennas.In practice application,it is easy to cause large fluctuations or even blind spots of radio coverage.At the same time,the current researches on radio coverage in tunnel environments mostly use plane waves as incident waves.Few studies have combined the antenna beam patterns with the tunnel environments.Aiming at the existing problems and deficiencies in previous research,this paper combines antenna beam patterns with tunnel environments,analysis the radio coverage in tunnel environments when transmitting antennas has different parameters.A novel high gain,low side lobe level left/right-handed structure leaky-wave antenna is designed,which is verified that it produces better radio coverage in tunnels than existing antennas.The main research and innovations of this paper are summed up as the following three points:1.The effects on radio coverage in rectangular tunnels of different kinds of transmitting antennas is studied.Dipole broadside array antennas,dipole endfire array antennas and Yagi antennas are used as transmitting antennas.The effects on radio coverage in tunnels of antenna beam widths and gains are analyzed under the same radiation power.We found that when using same type of transmitting antennas with different beam widths,the law of radio coverage are similar.As gain of transmitting antennas increases,received power of the receiving antennas increases accordingly.2.The path loss model in confined space has been used to divide the break points to distinguish the near-field and far-field in tunnels.The median(50%)power,the 90%power and the 95%power have been proposed to estimate the radio coverage effect in the far-field.We find that when using same type of transmitting antennas with different beam widths,the median power,the 90%power and the 95%power in the far-field are linear related to the gain of transmitting antennas.Therefore,with the increase of the gain of transmitting antennas,the received power in the far-field increases linearly.This shows that if necessary,the radio coverage in tunnels can be improved by increasing the gain of transmitting antennas.3.A novel left/right-handed leaky-wave antenna with high gain,narrow beam and low side lobe level is designed.According to the low of radio coverage in tunnels in above research,we designed a novel substrate integrated waveguide leaky-wave antenna which is suitable as a transmitting antenna in tunnel environments.The side lobe level of the antenna is reduced by using Taylor aperture distribution,and the gain of the antenna is improved by applying a Chebyshev current array.The radio coverage in a rectangular tunnel of the proposed antenna is analyzed by ray-tracing method.It is proved that this novel antenna has a better radio coverage than traditional antennas such as Yagi antennas when using in tunnel environments.