The Wideband Electromagnetic Pulse Generator Based On Switch Ocillator

Generation of wideband electromagnetic pulses is widely studied along with narrow and ultra-wideband high power microwaves (HPM). Practical applications require compact and portable sources. The transmission line (TL) switch oscillator is an important way to produce wideband electromanegtic(EM) pulse. In the thesis the mechanism and operation characteristics of the switch oscillator is investigated, upon which a tunable EM pulse is obtained. The central frequency lies within 270MHz to 380MHz. The relation between the structures of the oscillator and pulse output is analyzed, which lay the basis for future practical designs.The detailed work includes the following:1. Upon analyzing and comparing the techniques of the wideband generators and antennas, a compact wideband generator is realized using the following scheme: a quarter wavelength transmission line switch oscillator is used to generate wideband electromagnetic pulse, an oil switch is used for the self-breakdown switch and a single-cone antenna is used for the wideband radiation. This combination results a simple and compact design.2. The working mechanism of the quarter wavelength oscillator is theoretically analyzed. Results show that the damped oscillation signal can be generated, and the center frequency can be adjusted by adjusting the length of the TL. By using appropriate connections between the oscillator and the antenna, the matching problem can be solved, and the antenna voltage is also increased. The above principle is verified by circuit simulation.3. The coaxial single-cone wideband antenna is analyzed numerically by FDTD simulation, results show that the VSWR is less than 1.5 for the frequency range between 0.2 GHz– 0.8 GHz, and the direction of the maximum radiation is 55 degrees off axis. By importing the pulse signal from the oscillator into the antenna, it is found that the radial TL of the oscillator affects the stored energy, the central frequency and the bandwidth. The PIC simulation is also conducted to show how EM wave is reflected and transmitted in the oscillator.4. Based on above simulation, the design is optimized, with length of the switch oscillator 30 mm, radius of the outer conductor 62 mm, radius of the inner conductor 56.8 mm, the height of the cone antenna 190 mm, and diameter of bottom 198mm. Calibration of the antenna show that it has gain of 4.2 dB within 0.2 GHz– 1.0 GHz. Experiment results show that wideband radiation is obtained, whose output central frequency can be tuned between 270 MHz– 380 MHz by adjusting the radial TL, with the percent of bandwidth changing between 23%—11%.