Klystron Filter Output Circuit

High power Klystron is a kind of microwave amplification device which has high power, high gain and high efficiency and has been widely used in radar, communication, TV broadcast, particle accelerator and industrial microwave heating. In the application of broadband, klystrons using mechanical tuning, stagger tuning, filter-loaded output circuit, distribution output circuit, traveling wave output circuit and multi-beam technology, traveling wave tubes and cross-field amplifiers are three main types of high power, broadband microwave amplified devices in communication and radar systems.The output circuit is one of the most important parts of a klystron. The structure and characteristics of output circuit have decisive effects on output power, efficiency, bandwidth and stability of the whole klystron. In the manufacture of an actual klystron, cold test of a klystron spend much money and time. The workers need to spend a lot of time on cold test and modulation on structure geometry to acquire ideal frequency-broadband properties. Therefore, Computer-Aided Design (CAD) technology has been developed and used to simulate accurately the interaction between electron beams and radio frequency fields in klystrons, and can also be applied to the design of klystrons in many countries.In this paper, the theory and designing method of filter-loaded output circuit of klystrons based on equivalent circuit model were introduced. A computer code for designing filter-loaded output circuit was programmed using MATHCAD. This code can be used to calculate basic parameters of output circuit which meet design demand of klystrons and have optimal impedance-frequency character. The gap impedance of output circuit also was calculated based on equivalent circuit model. It also can be used to calculate and analyze the effects of these parameters on the bandwidth. These preliminary designed parameters can supply a rough guide for the engineering design.In this paper, the resonant cavity of filter-loaded output circuit was analyzed by solving field equations and the calculation formulas of resonant frequency and characteristic impedance of resonant cavity were presented. An actual klystron has been computed using electromagnetic software MAFIA and the results agree well with the experimental results and the erroneous are within 0.04% and 5.3% respectively. We often have to compute open system like waveguide loaded cavities when simulating klystrons. In this paper, the resonant frequency and quality factor of waveguide loaded cavity were computed using MAFIA according to the frequency characteristics of reflection coefficient phases at the waveguide port of waveguide loaded cavity.In this paper, the transient coefficient S12 of klystron filter-loaded output circuit was computed using CST Micro Wave Studio, and the effects of the parameters of output circuit on the transient coefficient were also analyzed. According to the microwave circuit theory, the circuit from the gap of output cavity to the output load in the output circuit can be equivalent to network of a two-port microwave system which is reciprocal without loss. According to the variation of reflection coefficient phases at the port of waveguide when the gap is open, short and tiny disturbed, the method of computing gap impedance was presented in this paper. In addition, the method of computing gap impedance was also presented according to impedance matrix of network of two-port.