Study On Slow-wave Substrate Integrated Waveguides And Their Applications For Designing Miniaturized Microwave Components And Antennas

Multibeam antennas can generate multiple high-gain directional beams,and each of them points to a different user.Multibeam antennas are large in volume because they consist of bulky beamforming networks（BFNs）.With the development trend of wireless communication systems to miniaturization and integration,multibeam antennas need to be miniaturized.Substrate integrated waveguide（SIW）combines the advantages of microstrip and metallic waveguide,exhibiting the merits of low cost,easy integration,low loss,and easy manufacturing,so it is suitable for designing multibeam antennas.In order to realize the miniaturization of multibeam antennas,slow-wave structures（SWSs）can be adopted into SIW,forming the slow-wave SIW（SW-SIW）.Slow-wave structures can introduce additional distributed capacitance and inductance,reduce the phase velocity and guided wavelength of electromagnetic（EM）wave.So the physical size of microwave components and antennas can be decreased.With the development trend of wireless communication systems to miniaturization and integration,this dissertation aims at the urgent demand of wireless communication systems for miniaturization and integration of multibeam antennas.The design method of SW-SIW is extended,realizing the miniaturization of SW-SIW while expanding the impedance bandwidth of SW-SIW.A series of miniaturized microwave components based on the SW-SIW are designed,miniaturization and good transmission performance of microwave components are achieved simultaneously.The miniaturization method of microwave and millimeter wave antennas based on SW-SIW is studied,antennas are miniaturized while maintaining the radiation performance.A miniaturized Butler matrix based on SW-SIW is designed,meanwhile good transmission performance of SW-SIW Butler matrix is realized.Based on the proposed SW-SIW Butler matrix and SW-SIW slot array,an SW-SIW multibeam antenna with four beam pointing in different directions is studied and designed.The main work of the author and the contributions of the dissertation are summarized as follows:1.The design method of SW-SIW is extended,realizing the miniaturization of SIW while expanding the impedance bandwidth of SW-SIW.A novel SW-SIW with enhanced slow-wave factor（SWF）and broadened bandwidth is proposed by simultaneously increasing the effective permeability and permittivity.The influences of the key dimensions in the slow-wave structure on the characteristics of the slow-wave factor,guided wavelength and cutoff frequency of the slow-wave transmission lines are studied.By loading slow-wave structures in the form of metallized blind via-holes and shorted patches,the distributed capacitance and inductance are enhanced,the effective permittivity and effective permeability are accordingly increased.The impedance matching between SWS-loaded and SWS-unloaded parts of SW-SIW can be significantly improved.The wave impedance along the periodical slow-wave structures is stable,leading to broadened operation bandwidth.Compared to the normal SIW,the transverse size of the proposed SW-SIW is reduced by 53%and the longitudinal size is reduced by 73%.The fractional bandwidth of the proposed SW-SIW is91.5%.The proposed SW-SIW has high size reduction level and wide fractional bandwidth.2.A series of miniaturized microwave components based on the SW-SIW are designed,miniaturization and good transmission performance of microwave components are achieved simultaneously.Firstly,a SW-SIW miniaturized 3-d B quadrature short-slot coupler is studied and designed.By loading the slow-wave structures in the form of metallized blind via-holes and shorted patches,the effective permittivity and permeability of the coupler are increased,so the transverse and longitudinal size of the coupler are decreased.The coupling slot length is reversely proportional to the propagation constant difference between the TE₁₀ and TE₂₀modes in the coupling region,the size of coupler can be further reduced by adjusting the size of slow-wave structures to enlarge the propagation constant difference between the TE₁₀ and TE₂₀ modes.Secondly,when the input port and isolated port of a 3-d B quadrature coupler are excited by two signals with the same amplitude and quadrature phase,these two input signals are in phase at the coupled port and out of phase at the through port.Therefore,an SW-SIW miniaturized crossover is designed by cascading two identical SW-SIW miniaturized 3-d B quadrature couplers.Thirdly,a 45°phase shifter and a 0°phase shifter are designed by changing the propagation constant of EM wave facilitated by adjusting the size of the slow-wave structure in the SW-SIW transmission lines.Compared with the conventional SIW delay line and unequal width phase shifter,the sizes of the proposed SW-SIW phase shifters are smaller.3.The miniaturization method of microwave and millimeter wave antennas based on SW-SIW is studied,antennas are miniaturized while maintaining the radiation performance.Firstly,an SW-SIW miniaturized slots array is proposed.The transverse size of the slot array is reduced by increasing the effective permittivity and permeability facilitated by loading the slow-wave structures in the normal SIW slot array.Compared to the normal SIW slot array with the same operating frequency,the transverse size of the proposed SW-SIW slot array is reduced by 40%without sacrificing the antenna performance.Secondly,a miniaturized SIW H-plane horn antenna with gain-enhancement is proposed by symmetrically loading the slow-wave structures in the form of a metalized blind via-holes in the flare region of the horn.The slow-wave structures can reduce the phase velocity around the center line of the broad wall.The cylindrical wave in the flare region of the straightforwardly shortened horn is changed to quasi plane wave.The phase distribution on the radiating aperture turns to be relatively uniform.The large phase difference is compensated between the center and edge on the radiating aperture caused by reduction of horn length.The horn antenna size is reduced in longitudinal direction with increased antenna gain.Compared to the optimum SIW horn,the longitudinal size of the proposed SW-SIW shortened horn is reduced by 53%and the gain is increased by 1.1d B.4.The miniaturization method of Butler matrix based on SW-SIW are studied,miniaturization and good transmission performance of Butler matrix are achieved simultaneously.Combined with the above SW-SIW slot array,a multibeam antenna with four different beams is designed.Firstly,based on the above SW-SIW transmission lines,couplers,crossovers and phase shifters,a miniaturized Butler matrix based on SW-SIW is studied and designed.Compared to the normal SIW Butler matrix operating at the same frequency,the size of the proposed SW-SIW Butler matrix is reduced by 75.5%.Secondly,by cascading the SW-SIW Butler matrix and SW-SIW slot array,a SW-SIW miniaturized multibeam antenna is designed.The proposed SW-SIW multibeam antenna can generate four directional beams pointing in the directions of-59°,-32°,32°and 59°.A prototype of the proposed SW-SIW multibeam antenna is manufactured and measured,measurement results agree reasonably well with the simulation ones,which verifies the feasibility of the proposed SW-SIW miniaturized Butler matrix and multibeam antenna.