Analysis For Transmission Characteristics Of Ridge Waveguide By Finite Element Method

As one of the important high-frequency communication device, ridged waveguides have been widely used as microwave transmission lines in wireless communications, space technology, electromagnetic compatibility (EMC), and electronic counter-measures (ECM). With the increasing modernization and informationization of Chinese railway system, microwave components such as ridged waveguides have been employed in railway transportation information system and control system. For example, the double-ridged hump radar speed meter has been equipped in most of the railway yards. Ridged waveguide components have been widely employed in microwave wireless communication system in high-speed rail (HSR).The purpose of the present study is to determine the transmission characteristics of ridged metallic waveguides with complex cross-sections. Two novel ridged waveguides with triangular ridges and inverted-trapezoidal ridges were first proposed in this thesis. Finite element method was implemented in Matlab, and transmission characteristics such as cut-off wavelength, single-mode bandwidth, characteristic impedance, attenuation and power handling capability for ridged rectangular waveguides, ridged trapezoidal waveguides, ridged inverted trapezoidal waveguides and ridged triangular waveguides have been analyzed systematically. The inverted-trapezoidal waveguide is especially suitable for single-mode transmission because of its large cutoff wavelength of dominant mode, lower characteristic impedance and higher power handling capability. Double ridged waveguide with ridges on the narrow side and ridged triangular waveguides are ideally suitable for microwave filters because of their narrow single-mode bandwidth. Dependence of transmission characteristics on asymmetrical ridged structures have been studied which is almost the same as those of symmetrical structures. The antipodal ridge waveguide has larger cutoff wavelength and smaller single-mode bandwidth. It is suitable for the case where narrowband operations are required. Ridged waveguides with complex cross-sections provide a possible way for waveguide miniaturization. It should be possible to fabricate microwave components at considerable saving in size and weight with high integration.Another important contribution of this thesis is in studying the dependence of waveguide deformation on the transmission characteristics of normal single- and double-ridged waveguides. For the case of dislocation deformation, the influence on the cutoff wavelength and single-mode bandwidth is about 3% and can be ignored if the critical deformation is within 10%。For the case of deformation due to the external force, the transmission characteristics will be changed dramatically and the performance becomes worse. From practical engineering point of view, the variation of major transmission characteristics can be within 10% if the mechanical deformation doesn't exceed 8%.Through the detailed numerical study of various ridged waveguides with complex cross-sections, this thesis presents systematic information for design of novel microwave and millimeter-wave ridged waveguide devices and provides a solid theoretical basis for expanding their application area. Numerical results in thesis are considered to be highly helpful in the design of various ridged waveguides in practical microwave engineering.