Study On The Cylindrical Qusi-optical Short Millimeter Wave Radiation Sourses

With the development of military technology, the performance of the band, efficiency, and power of microwave tube need to be increased timely. The microwave whose wavelength is 3mm~1mm is valuable to be developed. It can be used in imaging radar, precision-guided munitions, fluoroscopy images, detection of biological weapon and EM sphere in electronic warfare. These applications ask for high-performance characteristic radiation resource. This is also the key point for the high power microwave evoluting to short millimeter wave. The frequency spectrum density of open qusi-optical cavity is almost a constant. It has larger size and high quality factor under very short working wavelength, while it be working at highermodes. It has potential to get higher output power in short millimeter wave band. In this thesis, the detailed investigations on the cylindrical quasi-optical systems are approved by the theoretical analysis, particle-in-cell (PIC) simulations and experiment study. The aspects which this dissertation presents about are as follows:1. Study on SP radiation characters of open column grating by using PIC methods. When a single bunch of electron passes through the surface of column grating, SP radiation will be inspired and the evanescent wave also can be observed. Latter frequency is a constant while SP radiation's frequency is a function of measurement angular; when a chain of bunches go across the column grating, SP superradiation can be observed by observing the bitmap of tangential magnetic field. SP superradiation's frequency equals to the tines of bunch's frequency. It has frequency locking properties. The radiation enhances at special angle; when using continue electronic beam to pass over the grating surface, we can also observe the SP superradiation in tangential magnetic bitmap. Its frequency is times of fundamental wave's frequency. Under the situation of the same grating period length, the same groove depth and the same groove mouth width, triangle groove column grating has the highest amplitude of tangential magnetic field at second harmonic. That means it has highest radiation power, while the inverse echelon groove column graing has the lowest radiation power.2. Study on open column grating structure's dispersion characteristics. Mode-matching method is used to get dispersion relation and coupled impedance function of rectangle groove column grating. Those equations are solved by MATLAB. The relationship between grating parameters and dispersion relation is also discussed. The profile of an arbitrary shaped groove can be replaced by a serious of linked rectangular staircases. At the boundary of two adjacent rectangles, the admittance meets the condition of continuous. Using the recursion formula of admittance, we can get the admittance at the mouth of groove. So the dispersion relation of arbitrary groove column grating can be obtained by the boundary conditions and admittance. The numerical analysis shows that inverse echelon groove column grating has a stronger dispersion relation than other shapes, while the triangle shaped groove column grating has a higher frequency than others.3. The small signal analysis of open column grating structure. A thin hollow electron beam is employed in the open column grating system. Beam-wave interaction linear model of open column grating is obtained by field matching theory. By using the step condition on the thin hollow beam surface and other bournary condition, dispersion equation is obtained. Numerically results show that when the operate frequency is fixed, there exist optimum beam parameters and geometercal parameters which can obtain maximum gain. And the triangle-shaped groove can provide wider band and lower gain.4. Nolinear simulation of beam-wave interaction in qusi-optical system. PIC method is applied to study the cylindrical qusi-optical system. The bunching of the beam and the field distribution of the system are analyzed. The relationship between output frequency, power and angle is also studied by simulation. In the system, operation frequency is decided by the intersection point of electronic beam and dispersion curve of column grating. The working mode can be called surface wave mode. The column grating acts as a device to select the frequency. The results of simulation match well with the cold test experiment results. Different shaped groove gratings inspire different working frequencies in the system. And the output power is also affected by the groove shape. Inverse echelon shaped groove column cylindrical qusi-optical system has higer outpur power. Inverse mirror cylindrical qusi-optical system is also shown in this thesis. When the electronics beam radius is bigger than the former system, higher current and higher power can be realized.5. Experimental study on cylindrical quai-optical system. Based on the former chapters, a cylindrical quai-optical experiment system is established. The experiment system contains the design of egun, magnetic coil, wave channel supporting rings and output horn. Using the physical experiment condition data, we do the simulation again and get 2.4MW output power under those conditions. In the experiment, 1.2MW output power has beem detected. This experiment results do not match well with the simulation results. This study provided a feasible method of designing high power output W-band radiation source.