Microwave Window Theoryand Design

The microwave window is a important part of a microwave tube,not only it ensure the microwave electronic devices works in vacuum condition, but also makes inputting and outputting of microwave energy smoothly at the occasion of the minimum reflection,and guarantee to avoid the happening of oscillation.The box-type window has a lots of advantage,such as simple structure,easy to process,wide bandwidth, the surface electronic field of the chip is very low,ease to cool of and so on.So it is used in many situations of vacuum devices like TWT,and magnetron devices, gyrotron devices, klystron devices,Accelerator devices and so on.In previous studies of the box-type window mostly used ceramics as its window chip,in this paper we will focus on the CVD diamond and sapphire windows chip to discuss and simulation.At the same time we will discuss many kinds of window materials and summarize, analyze and compare them. About the structure,many and many scholars adopted the classical type of box window except a small part of researchers who used improved structures,the improved structures includes putting additional inductance chip to mach the impedance of cylindrical wave guide and impedance of window chip.There are also some developers changes his way to design cutoff wave guide window,or to try the gradual change node structure.In this paper,we still use the classic one and chose the sapphire material and CVD-diamond as the chip.We will discuss the equivalent circuit of window in the case of sapphire window chip to extend the classical theory. We also simulates the sapphire and CVD-diamond window and a terahertz window,Through design and simulation we found that sapphire and diamond suitable for box-type window in high frequency band.The contents of this article includes the following sections:The equivalent circuit of the traditional box-type window theory is analyzed and deduced, and we extended discussions in the case of a sapphire window chip of box-type window equivalent circuit.We enumerated in detail and compare the various of window materials, and focus on the structure and characteristics of the sapphire and CVD diamond. We analyzed the power and voltage defined impedance ratio formula, it is a useful summary and supplement to the traditional theory. It has some theoretical significance when scholars choose window materials gradually tend to sapphire andCVD-diamond. We also analysis and elaborated the box-type window ghost mold causes and the ways to avoid,and derived the formula window chip temperature rise.In this paper we designed and simulated a kind of sapphire window chip of pill box window,Combined with the needs of the project we manufactured one and tested it, the test results shows that its performance meets the project requirement. In this paper we also designed a W-band simulation of CVD-diamond window, and a frequency of180GHz-220 GHz terahertz window, the simulation results shows that CVD-diamond as a terahertz window chip is a good choice in theory.