Ka-band Rectangular Coupled Cavity Traveling Wave Tube

Electronic vacuum devices dominant in high power and high frequency microwave devices. Travelling Wave Tube(TWT) is a typical representative of them, which is used in remote communications and radar technologies, for example. There are two types of TWT in commonly use, Helix Travelling Wave Tube and Coupled-Cavity Travelling Wave Tube(CCTWT), whose output power and band-width is much bigger than semiconductor devices. It is especially useful in satellite communications, space communications and radar technology.A type of rectangle CCTWT was researched in this paper, whose RF system is formed of periodic rectangular coupled cavity chain. Designing rectangular coupled cavity chain with slots is a way to reduce the demanding requirements of geometric dimensional tolerance of slow-wave structure on the fundamental. This structure has good electric characteristics as traditional circular structure, it has high mechanical strength, can be exposed to high heat load. It consists of a large slotted copper shell and a group of rectangular diaphragm with coupling window, and the diaphragms are inserted into the slot Pre-processed on the copper shell. This structure can ensure the cavities with high homogeneity of electrical parameters in the length direction of slow-wave structure, and can limit the tolerance range in the assembly of the slow-wave. What’s more, selecting diaphragms to assemble slow-wave system can be considered, so "cold" measurement can be done and single cavity parameters can be adjusted before the final assembly of the entire device.At first, theoretical calculation methods was used to analysis Rectangular CCTWT. Perturbation theory was used to analysis the coupling of the cavities adjacent; the relationships of dispersion and pierce impedance with the structure of cavity and slot are researched qualitatively.Computer simulation techniques were used to cast savings, improve the design efficiency and reduce the design cycle during the design for experiment. The cold-test structure was calculated by CST microwave studio, the dispersion curve was got, as well as its pierce impedance. An optimized structure of slow-wave was got eventually by analysis the affects of the geometric parameters of the slow-wave to the parameters above.And then CST particle studio was used to study the interaction between the electron beam and electromagnetic wave. By sweeping CCTWT’s operating voltage, the voltage suitable for the operating of the CCTWT was found. At this voltage, the CCTWT has stable large power output.To solve the band-edge oscillation occur during Rectangular CCTWT’s operating, attenuators are used. The affect of attenuators’conductivity, quantity and position to the attenuation were studied. Under the role of attenuators, band-edge oscillation was effectively inhibited, making the Rectangular CCTWT an constant Output Power and pure spectrum.In this paper an optimized slow-wave structure of Rectangular CCTWT was designed finally through theoretical and computer simulation. Its Bandwidth is wider than500M, power output is larger than15kW and Gain is up to32dB.