| In recent years,with large numbers of subways,mountain railways and rail tunnels built,and the automatic train control systems based on wireless communication(CBTC)extensively used,the effective coverage of radio wave in confined spaces has become one of the important research topics.The leaky waveguide,as an important method for the radio coverage in confined space,has been paid much attention and frequently used for years;for some ultrahigh frequency bands and some special applications in confined spaces,the radio coverage is then realized by using low-cost leaky-wave antennas.Therefore,the researches on the leaky waveguides and leaky-wave antennas are significantly important.Besides,with the development of the next generation of communication system,the current wireless communication systems for the 2.4 GHz and 5.8 GHz bands are no longer adequate for the requirements.Therefore,it is necessary to find the new radio coverage systems for high frequency bands in confined spaces.Based on the confined spaces in the CBTC system and the mobile communication system,this dissertation works on the new leaky rectangular waveguides and leaky-wave antennas,and provides a radio coverage method with high efficiency in confined spaces for the current frequency bands and the next generation communication system.The main work and innovation points of this dissertation are concluded as follows:1.A computation method based on the numerical computation for the propagation constant of leaky rectangular waveguide is proposed,analyzing the variation rules with the working frequency and the slot size;at the same time,an equivalent circuit method is proposed and then the periodic leaky rectangular waveguide is equivalent as a cascaded circuit.The expression for the propagation constant of leaky rectangular waveguide with the structural parameters is deduced,for further revealing the variation mechanism of the propagation constant of leaky rectangular waveguide changing with the structural parameters.2.A combined slotted leaky rectangular waveguide is designed for circular polarization radiation in the working near field,for the application background of CBTC at 5.8GHz.The generation mechanism of the circularly polarized wave is analyzed and the leaky rectangular waveguide is fabricated and measured.The result shows that the combined slotted leaky rectangular waveguide with semicircular slots and triangular slots,could produce the circularly polarized radiation,respectively with ranges of 50° and 40° in the circumferential direction.3.A structure of the dielectric waveguide is proposed for the application of theradio coverage in the confined spaces at the 75GHz frequency band.The longitudinal attenuation properties of the basic homogeneous dielectic waveguide changing with the cross-sectional size are researched firstly and the size of the wavegudie are obtained for a low transmission loss;then the periodical dielectric slabs are added to the homogeneous waveguide,to produce the leaky wave,and the radiation properties changing with the structural parameters of the dielectric slabs are studied.It indicates that the leaky waveguide could generate the efficient radio wave coverage within a wide angle range in a far distance.4.A low-loss periodic circularly polarized leaky-wave antenna with low sidelobe at 45GHz frequency band is proposed based on the planar Goubau transmission line.By designing the radiation unit cell and their relative locations,the antenna could achieve the good circular polarization and low sidelobe level properties,with a wide CP band.Besides,based on the theory of the right/left-handed transmission line,a leaky-wave antenna is proposed to radiate a broadside beam. |
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