Study On Coaxial Interlaced Disk-loaded Waveguide And Its Applications

Millimeter-wave radiation sources with high power, wide bandwidth and high efficincy are attractive for many applications, such as high-date-rate communication, radar and electromagnetic countermeasure. Due to its outstanding combined performances in power capacity and band width, the traveling wave tube plays important role in millimeter-wave radiation. The helix cuircuits, as a traditional slow wave structure has wide bandwidth, but its power capaplity is small. Meanwhile, as the working frequecy increases, the fabrication of helix circuit becomes difficult. Recently, the all-metal slow wave structures attract many scholar’s interest for their peculiarities:large size, high precession of manufcturing and assembling. Because of these advantages, the all-metal slow wave structures are widely used. The disk-loaded cylindrical waveguide is one of the most important slow wave structure in the all-metal slow-wave structures. In this dissertation, we have made detailed studies on the coaxial interlaced disk-loaded waveguide. The results show that it has important application merit in multi-beam millimeter-wave traveling wave tube.This dissertation does a detailed analysis for the coxial interlaced disk-loaded waveguide on three aspects, including high frequency characteristics, transmission characteristics and beam wave interaction characteristics. The reaserch shows that the coaxial interlaced disk-loaded waveguide can be applied as slow-wave structure for multi-beam millimeter wave traveling wave tube. The major achievements are listed as the followings:1. The dispersion equation of the coaxial interlaced disk-loaded waveguide slow-wave structure is derived by means of multi-conductor transmission line method under the condition of thinking the thickness of disk. Meanwhile the dispersion equation is solved by means of numerical computation method, and the results are agree with those from software simulation. The coaxial interlaced disk-loaded waveguide could get wide bandwidth when select proper structure parameter. The theoretical analysis is the foundation of the research, meanwhile it provide the valid model parameter for the application.2. It is analyzed that the change of structure parameter affects dispersion characteristic and interaction impedance of the coaxial interlaced disk-loaded waveguide using electromagnetic simulation software ANSOFT HFSS. The results of research show that the inner conductor radius ra and period length L have greater effects on high frequency characteristic than other structure parameters. Along with the decrease of ra, the interaction impedance increase obviously. The phase velocity can be decreased apparently by reducing the period length L.3. In order to improve the high frequency characteristic of the coaxial interlaced disk-loaded waveguide, two different ridge-loaded structures are proposed: edge-ridge-loaded structure and middle-ridge-loaded structure. The results of research show that the normalized phase velocity of the edge-ridge-loaded structure reduced apparently compared with that of the coxial interlaced disk-loaded waveguide, from 0.29 to 0.24, decreased 17.2%, however the coupling impedance changes slightly. The middle-ridge-loaded structure has great effect on interaction impedance, and the loaded ridge makes the interaction impedance increased noticeably. When these two ridge-loaded structures are used as slow wave structure of the traveling wave tube, the operating voltage can be decreased and the beam-wave interaction efficiency is improved respectively. At the same time, some other kinds of disk-loaded cylindrical waveguide are investigated. The results show that the coaxial interlace disk-loaded structure can not only get weak dispersion but also make more contributions on decreasing the phase velocity than other structures.4. We also proposed a design scheme of the V band eight beams coaxial interlaced disk loaded waveguide traveling wave tube with peak power of 400 W. Furthermore, the process of the nonlinear beam-wave interaction in coaxial interlaced disk loaded waveguide is simulated by CST PIC-Solver. The investigation reveals that the reflection parameter S11<-25 d B is achieved. The traveling wave tube has a gain over 30 d B in the frequency range of 44.5-46.5GHz, and the electronic efficincy is about 4.3%. The maximum peak power is 462 W and the maximal gain is 31.1 d B. Therefore, the coaxial interlaced disk-loaded waveguide has potential application in multi-beam millimeter wave traveling wave tube.In summary, the coaxial interlaced disk loaded waveguide is an all metal slow wave structure with excellent high frequecy characteristics. The investigation of this slow wave structure is important to the millimeter traveling wave tube, especially as a new slow wave structure for the high power multi-beam traveling wave tube.