| With the continuous development of wireless technology,progress in design theory and processing technology,microwave,millimeter wave and even terahertz wave band circuits and antennas are attracting more researchers’ attention.How to realize a circuit with a compact size and excellent performance and how to realize beam control of electromagnetic waves,especially in the terahertz frequency band,has become the core of the research.This thesis mainly studies the application of microwave and millimeter wave substrate integrated circuits and the application of coding metamaterials for terahertz wave beam control.The main content of the paper and research contributions include the following three aspects:First:the application of hybrid substrate integrated circuits in directional couplers.A design method of a multi-layer half-mode substrate integrated waveguide 3-dB coupler is proposed.This method is based on the traditional rectangular waveguide Bethe hole coupling theory.By searching for the field distribution relationship between the substrate integrated waveguide and the half-mode substrate integrated waveguide,a convertion from substrate-integrated waveguide broad-wall couplers to half-mode ones are derived,which could simplify the design process of the half-mode substrate integrated waveguide broad-wall coupler.At the same time,combining with the special characteristic of substrate integrated circuits and advantages of multi-layer circuits in miniaturization,a compact half-mode substrate integrated waveguide strong coupling coupler with a wide operating bandwidth was designed.On this basis,by changing the topological structure of the coupler and the filter,a filtering coupler with a combination of filtering and coupling response is formed.Without increasing the size of coupler,the filtering response is introduced to improve the out-of-band rejection.As a result,a filtering coupler with better performance is proposed,which is more suitable for system integration.Second:the application of hybrid substrate integrated circuits with slow-wave effect.A substrate-integrated waveguide slow-wave transmission line based on complementary split ring resonantor(CSRR)is proposed.This method utilizes a strong loading effect of CSRR to modify the dominant mode of substrate integrated waveguide and excite the slow wave effect,thereby realizing a slow-wave substrate integrated waveguide transmission line.Such a slow-wave transmission line is simple in structure and excellent in performance,and has a wide range of application prospects.On this basis,using a steady phase velocity change brought by the slow wave effect,a miniaturized,broadband,and low-loss 90° phase shifter could be realized without changing the symmetry of the circuit.Combined with the miniaturized broadband 3-dB coupler designed in first section,a compact dual-layer high-performance substrate integrated six-port circuit could be achieved.This sheme is suitable for both substrate integrated waveguide and half-mode substrate integrated waveguide.The circuits could mutually transform to each other and are simple in structure,easy in design,excellent in performance,and suitable for various orthogonal modulation and demodulation systems.In addition,such a slow-wave substrate integrated waveguide transmission line can also be used to design a miniaturized coupler,and the slow-wave effect can be used to further reduce the size of the coupler.In order to reduce the interaction between the slow wave effect and the coupling function,the CSRR is placed on the shared broad wall of the substrate integrated waveguide transmission line.Such a structure realizes an E-plane coupling under slow-wave effect for the first time.Without affecting the performance of the coupler,the volume of the substrate integrated coupler is greatly reduced,and further miniaturization of the coupler could be realized.Third:the application of birefringent material liquid crystal in coding metasurfaces.A method for quasi-2-bit coding terahertz liquid crystal metasurface realized by resonant switching is proposed.Under the premise of improving the driving stability of liquid crystal,the realization method of multi-bit liquid crystal coding is greatly simplified,and the unwanted beam is effectively reduced.Through introducing interdigital electrode into metasurface,the birefringence effect of liquid crystal is used to realize independent control of two resonances of the metasurface,and realize a quasi-2-bit digital coding modulation.This control method can discrete the traditional continuous voltage control into a 0-1 control mode,so the traditional 1-bit digital programmable control system could be directly inherited,thus avoiding the more complicated multi-voltage control method.At the same time,a liquid crystal control method that works under the saturation voltage injects more robustness and repeatability into multi-bit coding,which greatly promotes the application prospects of liquid crystal materials in the field of digital encoding control.At the same time,it offers a reliable,low-cost and low driving voltage solution to terahertz wave single-beam manipulation. |
