Research On The Radiation Characteristics Of Leaky Waveguide And Leakv-Wave Antenna

Leaky waveguide and leaky-wave antenna have been widely used in the wireless communication systems. In recent years, with the increasing requirements of wireless communication quality and the rapid development of the automatic train control systems based on wireless communication, the efficient field strength coverage in confined space communication systems have drawn more and more attention. Therefore, the leaky waveguide and leaky-wave antenna with powerful capability of providing efficient field coverage in confined space become a hot research topic. This dissertation aims to study the novel leaky waveguide and leaky-wave antenna which can be used for efficient field coverage in confined space. It is mainly focused on the radiation characteristics, structural design and environmental suitability in applications of the leaky waveguide; meanwhile, the circular polarization leaky-wave antennas based on substrate integrated waveguide (SIW) which can be used in confined space are also discussed in this dissertation. The researches have great significance to improve the radio coverage performance and the reliability of the wireless communication used in confined space.The main work and innovation points of this dissertation are concluded as follows:1. In order to decrease the transmission loss at higher frequency, a new kind of leaky circular waveguide is designed to replace the leaky coaxial cable. The spatial harmonics and radiation characteristics of the leaky circular waveguide are analyzed based on the studies of the leaky coaxial cable, and the relationships between coupling losses and structure parameters are studied as well. It can be found that, compared with the leaky coaxial cable, both the negative order (m<0) harmonic radiations and the positive order (m≥0) harmonic radiations can generate leaky waves in leaky circular waveguide.2. The approach for analyzing the propagation constant of leaky circular waveguide is proposed using the numerical method, and the relationships between the waveguide parameters and the normalized propagation constant of leaky circular waveguide are analyzed. Based on the analysis, empirical formulas of propagation constant are derived via curve-fitting using all the data obtained from numerical method, which are very valuable for the investigation on the propagation constant, cut-off wavelength and the spatial harmonics of the leaky circular waveguide.3. A leaky circular waveguide with wire ridge is proposed. The wire ridge is added along the axial direction of leaky circular waveguide to maintain the polarization state of wave, which can improve the long distance transmission stability. In addition, a kind of patched leaky circular waveguide with adjustable coupling losses is proposed for complex environments. Compared with unchangeable coupling losses of the conventional circular waveguide, the coupling losses of the patched leaky circular waveguide can be easily adjusted by changing the parameters or period of the patches.4. Take snow coverage for example, the influences of environment on the radiation characteristics of leaky circular waveguide are discussed, and the way of reducing the influence of snow coverage is proposed. The results have shown that that the influences of snow coverage on the radiation characteristics of leaky waveguide can be decreased effectively. In addition, a method of placing a dielectric layer on the surface of the leaky waveguide is proposed, which can be used to increase the electrical distributions around the waveguide. This method can be used for the communication systems which are only working at the near field region of the leaky waveguide, while the radiation energy can be focused to the desired direction.5. A new kind of circular polarization leaky-wave antenna with N-shaped slots cut in the upper side of substrate integrated waveguide is proposed and tested. Simulated and measured results show that the antenna can realize circular polarization property in8GHz band and5.8GHz ISM band by properly choosing structural parameters and substrate dielectric constant.