Numerical Simulations Of Coaxial Bragg Reflectors

High-power radiation sources in millimeter and sub-millimeter waves have a great prospect of applications to radar, plasma heating, high-gradient linear colliders, and communications, and therefore, attract more and more attention in many countries. Microwave devices play an important role in high-power microwave technology. And as one of microwave devices, Bragg reflector is focused by researchers in the world.In the past years, Bragg structures have been widely applied as Electromagnetic Band-Gap periodic structures in cyclotron auto-resonance maser (CARM), free electron laser (FEL), and microwave field. Generally speaking, a Bragg reflector is regarded as the most suitable cavity structure in millimeter and sub-millimeter, because it can provide good mode selectivity and high quality factor for the selected mode.This dissertation designs a novel coaxial Bragg reflector, where both the outer wall and inner rod are corrugated with weak sinusoidal ripple, and makes the comprehensive study including numerical and software simulations. Several valuable academic achievements are obtained.Firstly, special simulations are done. Simulation results are compared with two ways. One way is that the reflection characteristics of the coaxial Bragg reflector are evaluated with the code we design according the coupled mode equations introduced in Chapter 2. Another is making use of CST software to analyze the characteristics. Compared to the first way, CST can provide us more comprehensive simulated results. The special simulation indicates that the corrugation phase and amplitude substantially affected the characteristics of the coaxial Bragg reflector.To optimize the characteristics, improved Bragg reflector with window distribution of the slot depth is present, based on a common technique in filter theory. The results in Chapter 5 show that the smooth of pass-band is improved effectively and the anticipative goal is achieved.Finally, two kinds of eccentricity between the outer-wall and inner-rod axes with the coaxial Bragg structure are studied in Chapter 6, because the two eccentricities always happen in practice. The results we obtain can offer the engineering references for the coaxial Bragg reflector.Main innovation points in the dissertation are as follows:1. The influence of corrugation phase and ripple depth on the bandwidth of coaxial Bragg reflector is studied by making use of the CST software. Specific simulation indicates the reflectivity of operating mode is close to 1 with a phase difference ofπ..2. The smoothness of pass band is well improved by introducing window techniques. The situations of Hamming window, Blackman window, Gauss window are studied employing CST.3. The effects of eccentricity between the outer-wall and inner-rod axes on the transmission band gap in a coaxial Bragg structure are analyzed. The influence of the eccentricity is minimized and becomes negligible when the phase difference is equal toπ.