Study Of Photonic Crystal Traveling Wave Tubes

Because can not be machined automatically, the cost of traveling wave tubes (TWTs) is very high, and the products are not completely consistent, so does the reliability. Further more, the transit of electrons becomes more difficult in TWTs when operating frequency is high. As a result, the cost of TWTs with middle or high outputting power is doubled inside millimeter-wave band, and the design of TWTs inside short millimeter-wave seldom succeeds. High cost and problem of electron transit extensively limit the application range and the development of TWTs. The cost of TWTs will decrease sharply if a kind of new material or structure which can be machined automatically is used. But the solution of electron transit inside high frequency band only bases on new mechanism of electromagnetic wave propagation.Photonic crystals (PhC) are new artificial materials with special electromagnetic response characteristics. Intruducing PhC into TWTs brings new possibility of decreasing cost and resolving problem of electron transit. First, the field distribution of PhC is diffirent from dielectric; the efficiency will increase if the dielectric of printed dielectric-base TWTs is replaced by PhC. Second, when operating frequency is inside or higher than THz band, the propagation attenuation of electromagnetic wave in metal waveguide will be high, but will be very low in PhC strucutred by dielectric. At last, operating with single higher mode is feasible in TWTs made up of PhC slow-wave circuit; accordingly, the problem of electron transit will be resolved based on the bigger beam tunnel available in PhC slow-wave circuit.The theme of this dissertation is TWTs with PhC circuit. The studied details include the modes and the propagation of electromagnetic waves in finite PhC, the basic theory and the design of PhC TWTs, and the design of electron optics for TWTs in which the cross-section of slow-wave circuit is big. The structure of this dissertation is presented in the following:Chapter 1 is introduction. In chapter 1, the background of research and the obstacles of present TWTs will be firstly explained. Then, the significance and the researching scope of this dissertation will be presented. In chapter 2, the main course is finite PhC. The modes and the propagation of electromagnetic waves in PhC metal waveguide, opening finite PhC and finite PhC with defect will be discussed.In chapter 3, the basic theory of PhC TWTs will be discussed. The basic three-layer structure of PhC TWTs will be put forward. The difficulty of design and the solving way, and the design ways by calculating eigenvalues and by calculating parameters of scattering matrix will be discussed.Three kinds of PhC TWTs with ribbon beam will be presented and discussed in chapter 4. The two kinds of PhC TWTs are the interdigital slow-wave structure and metal grating slow-wave strucutre with two-dimensional dielectric PhC, and the meander line slow-wave structure with PhC and cutoff-waveguide structures.In chapter 5, the topo structures of ring slow-wave structures based on ring-plane structure and Tunneladder slow-wave circuit will be firstly discussed. Then, the PhC slow-wave structure combining ring-bar slow-wave structure and high impedance surface PhC will be studied.For the usage of PhC in TWTs will make the cross-section of slow-wave strucutre become more bigger, in chapter 6, the electron optics system of TWTs with PhC slow-wave structure will be studied. An example will be presented, and the way will be shown by defining and calculating the coeffients of relation and sensitivity through the results of numerical codes.The chapter 7 is conclusion.