| With the development of high power microwave (HPM) technologies, great effortshave been made on increasing the output power levels and the frequency spectrum ofthe HPM systems. As one of the most important sectors in the HPM system,transmission and radiation system mainly dertermines the whole structure of the HPMsystem. On the other hand, narrow-band HPM source usually operates at single bandand has limited output power at present. An alternative methd for enhancing the outputcapacity of HPM system is taking advantage of waveguide-based power combiningtechnologies, not only for increasing the output power levels, but also for the frequencyspectrum of the HPM systems. In this dissertation, detailed investigations were carriedout on multi-channel dual-band radiation system for HPM applications, and it mainlycontains two kinds of orthogonal waveguide-based power combiners, dual-band coaxialwaveguide bends and coaxial dual-band horn. The theoretical, numerical simulation andexperimental investigations shows that it is a promising method for realizingmulti-channel multi-band HPM integrative radiation, which is significant for HPM insome special applications.The detailed contents and innovative work include thefollowings:1. A specific T-junction waveguided-based power combiner is proposed forcombining the X/X band microwave beams.Two kinds of metal plates are inserted into an overmoded T-junction rectangularwaveguide, and they play an important role in controlling propagation direction oflinearly polarized microwave. The basic structure of the combiner is designed, and itstravelling wave structure is a promising merit for compact designment whilemaintaining high power handling capacity. Also, the T-junction combiner can workingat single frequency or dual-band. Moreover, based on preliminary analysis of thisstructure, a T-junction waveguided-based power combiner with the centre frequency of9.5GHz is designed. The detailed numerical simulation and experimental results showsthat, two linearly polarized microwave beams with perpendicular polarization directionshave realized power combination and transmission separately. In the range of9.4GHz~10.0GHz, its transmission efficiency exceeds95%and the corresponding bandwidthwith can meet the requirements for narrow-band HPM applications. In the experiment,the radiated microwave power is about1.3GW with pulse duration of35ns, and no pulseshortening or breakdown phenonmenon occurs.2. A cross-junction waveguide-based power combiner is investigated, realizingpower combination of S/S band microwave beams in coaxial waveguide.According to the characterstics of TE11coaxial waveguide mode (Coa.TE11mode)and TE10rectangualr waveguide mode (Rec.TE10mode), a doughnut-shaped waveguide is utilized to design cross-junction power combiner. Furthermore, a modifiedcross-junction is developed for convenience, which has coaxial output port, compactstructure and high power transmission efficiency. A prototype of this combiner isanalyzed systematically, including the mode conversion processes and the reflectioncharacteristics, achieving some valuabe conclusions. Based on the requirements, across-junction combiner with center frequency of3.6GHz is designed, and the detailednumerical simulations shows that this structure also has high power handling capacity,and two linearly polarized Coa.TE11modes with perpendicular polarization directionshave realized power combination and transmission separately. Its’ power transmissionefficiency reaches98%at3.6GHz, and exceeds90%in the range of3.5GHz~3.7GHz.In addition, HPM sources usually generate TM01circualr waveguide mode (Cir.TM01mode), a mode converter is designed to realize mode conversion from Cir.TM01mode toRec.TE10mode, which is necessary for cross-junction combiner applications. As anexample, a TM01TE10mode converter at3.6GHz is designed and simulated. It has highconversion efficiency of over99%at center frequency, and in the range of3.36GHz~3.96GHz, it is greater than90%. Experimental investigations are focused on powerhandling capacity and mode conversion effect, which shows that the combiner has highpower handling capacity with GW level, and it realizes integration of powercombination and mode conversion. In the experiment, the radiated microwave power isabout1.1GW with pulse duration of32ns.3. A dual-band coaxial waveguide bend is studied systematically for changingmicrowave propagation direction for certain purposes.To realize dual-band HPM directional transmission, coaxial waveguide bend isstudied systematically after taking advantage of mode coupling theory, obtaining thegeneral and explicit formulas of the coupling coefficients. Firstly, single-band anddual-band coaxial waveguide mode converters with different structures have beendesigned, all of them have high mode conversion efficiency of over99%at centerfrequency, and experiment and numerical simulations agree well with each other.Secondly, overmoded90°coaxial waveguide bend is proposed to meet specialrequirements. In this part, the designed overmoded90°coaxial waveguide bend notonly has high power handling capacity, but also has high pure transmission efficiency,and transmission efficiencies of TE11modes with perpendicular polarization directionsare over99%at3.6GHz and9.5GHz. In the range of3.05GHz~3.85GHz and2.80GHz~4.30GHz, respectively, their transmission efficiencies of horizontal and verticalpolarized Coa.TE11modes are greater than95%. In the range of8.50GHz~10.02GHzand8.50GHz~10.50GHz, respectively, their transmission efficiencies of horizontal andvertical polarized Cir.TE11modes are greater than95%.At the same time, multi-bandcoaxial waveguide bend with multi-coaxial structures is designed for specialapplications. Furthermore, rectangular waveguide bend and rectangular waveguide with variouscross sections are studied according to mode coupling theory, achieving many valuabeconclusions, which are theoretical foundation for quickly designing different passiverectangular waveguide components.4. Based on flare angle horn, a dual-band horn antenna with coaxial feed structureis designed for S/X band radiation.In this part, a new kind of dual-band horn antenna with high power handlingcapacity is proposed, which consists of coaxial feed structure and flare angle horn. Lowband microwave is fed by Coa.TE11mode, and high band microwave is fed by Cir.TE11mode. Based on the specific structure of the horn antenna, mode matching method isutilized to determine scatter matrix of each discontinuity in cross section. To obtain theoverall scatter matrix of the antenna, it is necessary to progressively cascade the scattermatrixs, and the overall scatter matrix determines the propagation properties of the hronantenna. Farfield radiation pattern of the dual-band antenna can easily get by usingmode expansion technology. Furthermore, a dual-band antenna at3.6GHz and9.5GHzis designed, and theoretical and numerical simulations agree well with each other. Itreveals that the dual-band antenna has high power handling capacity with several GWslevel, and good farfield radiation pattern at each band has been achieved. |
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