Thz Quasi-optical Cyclotron Amplifier Input System Research

The development history of human technology is always related with thedevelopment and utilization of the electromagnetic spectrum closely. Meter wave,decimeter wave, centimeter wave have been applied more and more widely. At thesame time, the study of the microwave spectrum is expanding to the millimeter andsubmillimeter. All the study are almost based on two methods: the first one is toexpand the traditional microwave device to the waveband of millimeter andsubmillimeter, and the second is focused on the working principle of millimeter andsubmillimeter wave and new microwave device.The characteristics of millimeter wave include its shorter wavelength, widerfrequency bandwidth and greater attenuation when it propagates in the atmosphere.Submillimeter also has the characteristics of short wavelength, high frequency,meanwhile even more wider frequency band. For these features, the submillimeter hassome special properties in the electromagnetic spectrum which make submillimeterhave been many important applications in many fields such as astrophysics,information science and technology, bio-medical engineering. Nevertheless, there aresome problems for traditional microwave device worked in the band of millimeter andsubmillimeter. Hence, traditional microwave device can just work in the band ofmillimeter with very low export power. However, the appearance of gyrotron amplifierfills the gap of high power device worked in millimeter and submillimeter waveband.The gyrotron amplifier is mainly including two parts: the first part is the inputsection, the input section consists of four WR4waveguides, one WR28waveguide,two transition structures from WR4waveguide to WR28waveguide and two WR4waveguides with the partial angle of900. The second part is a confocus cylindricalquasi-optical waveguide, whose major role is to reach the electromagnetic fielddistribution we need to make the effective exchange of energy betweenelectromagnetic field and electronic. Meanwhile, the important role of the structure isits good mode selectivity inside the waveguide, the mode of TE0n, TE1ncan exist inthe internal of the waveguide steady, thereby improve the mode space of the interior of the waveguide.The gyrotron amplifier was simulated by CST microwave studio during the designwhich improves the efficiency of device design generally and decrease the fabricationcost of device by adjusting the geometric parameter of the device structure. By CST,several S21parameters in some parts of input structure were calculated. And lower thetransmission loss of TE0nmode, TE1nmode in input structure by sweeping andimproving the geometrical parameters. Then, the non-confocal cylindrical quasi-optical structure was simulated considering the problems which may appear in thefabrication and got an optimized structure of gyrotron amplifier which is expected tobecome new millimeter wave and the millimeter wave transmission device.