| As key component in the vacuum electronics device,the RF window should not only have good sealing performance to ensure the structure reliable and vacuum seal,but also be‘transparent'to the electromagnetic wave,so as to ensure the normal transmission of signals inside and outside the device;its structural reliability,power capacity,and process achievability and other factors directly affect the performance of the vacuum electronics device.As the working frequency reaches the terahertz frequency band,on the one hand,due to the limitation of the size common effect,the feature size of the parts has rapidly decreased,which has brought great challenges to the processing and assembly of parts;On the other hand,there are strict requirements on the performance of the RF window:under the small and thin window disk,it can withstand enough atmospheric pressure difference to ensure good vacuum sealing;Can adapt to temperature,impact,pressure and other changes in environmental conditions,with good mechanical strength;High temperature resistance,good heat dissipation;The insertion loss should be small;wide bandwidth;Transmission performance is extremely sensitive to size.All these bring great difficulties to the design and process implementation.Therefore,how to obtain the RF window with broadband,low loss and high-power capacity in the terahertz frequency band has become an important topic in the development of terahertz vacuum electronics devices.In this paper,aiming at 220G Hz and 1.03THz travelling wave tube broadband RF windows,the simulation and analysis of broadband RF windows with different dielectric material window disk and types were carried out,as well as the design parameters and process implementation methods were obtained.The main theoretical,experimental work and innovative results are as follows:1.Design and implementation of 220GHz beryllium pill-box window.The initial parameters of the 220GHz beryllium pill-box size are calculated by using the equivalent circuit theory,and the physical model is established by using the 3D simulation software CST,and the size parameters are simulated and optimized.The welding is divided into two steps to adjust the air tightness and transmission performance of the pill-box window,so as to realize the reflection coefficient S11-20dB and transmission coefficient S21-0.8dB of in the 211GHz-232GHz pass-band.2.Design and realization of 220GHz sapphire improved pill-box window.Based on the equivalent circuit theory,the size parameters are calculated,and the size optimization and feasibility analysis are carried out by CST software.The improved structure has a larger area of window disk and metal contacting,which can greatly improve the reliability and assembly accuracy of vacuum seals.Screen printing method is used to metallize the window disk to ensure tightly seal with the window frames.After brazing,the transmission performance of the pill-box window achieves the reflection coefficient S11-20dB and the transmission coefficient S21-1.2dB within the218GHz-245GHz pass-band.3.Design and implementation of THz sapphire pill-box window.Four kinds of structure of RF window are designed.Size parameters and the influence of size error on performance are calculated by using CST software.The tapered transition RF window with larger transverse dimensions is selected for machining.In the window sealing,the active-welding ensures the air tightness of the RF window.At the same time,the optimal parameters of sapphire magnetron sputtering are obtained through a large number of experiments.Compared with the screen printed metal layer,the uniformity and consistency of copper and titanium metal layers after magnetron sputtering are better,which is conducive to mass production. |
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