Research On Three-mode Overlapped Two-gap Coupled Cavity Type Output Circuit

The trend of development for klystron amplifer is broad bandwidth, highpower and high efficiency. As the wide application in radar, require of instantaneousbandwidth of klystron is becoming stricter. The output circuit of klystron, which hassomething to do with the bandwidth and efficiency of klystron, is the core in theenergy output part, and its bandwidth determines the bandwidth of whole klystron.So it is necessary to research output circuit of hyper-broad bandwidth klystron. Inthis dissertation, how to enhance output bandwidth using three-mode overlappedtwo-gap cavity is researched. Based on 3-D field analysis method, three-modeoverlapped two-gap coupled cavity type output circuit is researched in detail bynumerical software simulation and equivalent circuit method. The gap impedancecharacter of this kind of output circuit is simulated numerically, and the effects ofstructure parameters on resonant frequency and gap impedance character areanalyzed. This simulation and research is significative for manufacture ofhyper-broad bandwidth klystron. The main achievements of this dissertation can beconcluded as follow:1. The theory of overlapped mode is analyzed further via equivalent circuitmethod. Possibility of overlapped three-mode is illuminated. Taken 3GHz forinstance, the gap impedance character of three-mode overlapped two-gap coupledcavity type output circuit is calculated combined with the theory of translation line.It is indicated that, 3dB bandwidth reaches 480MHz, while 1 dB bandwidth reaches 570MHz loaded by filter.2. In the platform of software package CST MWS, which is based on FiniteIntegration Method, taken center frequency f₀=3GHz bandwidthΔf=450MHzas example, 3D models for calculation are set up, and steps on how to design thiskind of output circuit are particularized; parameters of structure are given out. Thehyper-broad bandwidth of this kind of output circuit is proved, and the initial size ofcold test manufacture and direction for adjustment are provided, which are the maininnovate points in this dissertation.