Circularly Polarized Radiation Techniques For High Power Microwaves

As an important component of the high power microwave(HPM) systems, the HPM radiation antenna radiates the high power microwave with a certain polarization onto a target at a specified direction, and its electrical performance determines the overall performance of the HPM system in a great extent. Thus, study of the HPM radiation technology meeting the HPM system requirements is of great academic and application significance.In this dissertation, the HPM circularly polarized radiation techniques are deeply and systematically studied. Firstly, theoretical analysis and experiments are carried out to find out the HPM breakdown thresholds for the commonly used metal waveguides and dielectric materials. With the thresholds as the design basis, a large diameter low-directivity feed horn with high power capacity is designed by taking the advantage of the big aperture phase difference of the colonical horn. The field amplitude distribution in the feed aperture is uniform, which reduces the maximum electric field intensity on the feed dielectric windows and improves the power capacity of the feed. Secondly, a GW-level HPM circular polarizer is designed. With a gradual elliptical waveguide structure, the linearly polarized microwave wave is transformed into the circularly polarized microwave wave. According to the HPM transmission and radiation characteristics, the online power measurement device and the radiation field array measurement device are optimized and designed to measure the power capacity of the circularly polarized radiation system. Finally, the HPM circular polarizer and the high-power-capacity horn feed are combined as a HPM circular polarization feed, which is installed in the HPM beam waveguide antenna. Experiments results show that the circularly polarized high power microwaves are radiated out effectively and directionally, which meets the engineering application requirements.The main research works and achievements are outlined as follows.1. Based on the degeneracy properties of TE11 mode in the circular waveguide and the phase velocity difference between two orthogonal TE11 modes in the elliptical waveguide, a TE11-mode HPM circular polarizer with the gradual elliptic waveguide structure is developed. Without using any dielectric material or pin in the circular polarizer, its insertion loss is small, and its axial ratio is less than 1 d B in the frequency band 9-10 GHz. Moreover, its power capacity is more than 1 GW.2. Methods for transforming the linearly polarized waves into circularly polarized waves are studied, which reduce the maximum electric field intensity in the feed aperture and increase the power capacity of the HPM radiation system. The research results show that, with the same power, when the circularly polarized waves are radiated, the maximum electric field intensity on the dielectric window is 2 2 times of that when the linearly polarized waves are radiated, which provides new technical means for enhancing the power capacity of the HPM system.3. The HPM horn feed for the HPM beam waveguide antenna is designed. The electric field intensities in the feed apertue are less than 40 k V/cm. Within-10 d B levels, the E-plane and H-plane primary radiation patterns of the feed are equalized. When the angle is in the range of ±20°, the power fed to the first mirror of the HPM beam waveguide antennas is about 93%, and the phase fluctuation is less than 22.5°.4. Experimental studies are carried out on the HPM circularly polarized radiation system. The experimental results show that the power capacity of the linearly polarized HPM feed is about 1.5 GW for an X-band pulse with width of 20 ns. When the linearly polarized waves are transformed into the circularly polarized waves, the power capacity of the same feed dielectric window is not less than 2.1 GW. The results verify that the transformation from the linearly polarized waves to the circularly polarized waves can improve the power capacity of the HPM feed. The radiation system composed of the HPM circular polarized feed and the HPM beam waveguide dual reflector antenna are developed, and the effective HPM circularly polarized radiation has been achieved. Measured results indicate that the gain of the HPM beam waveguide dual reflector antenna with a diameter of 6m is about 53.2 d B, its efficiency is about 53%, and its axial ratio is about 2.5 d B.