Researches On Antenna And Beam Transformation By Using Quasi-Optical Techniques

Compared with light waves and infrared waves,millimeter waves have lower attenuation and can be operated under different weather conditions. In the meantime, millimeter waves have higher frequencies and broader bandwidths than microwaves have, giving rising to higher transmission rate of data, angular resolution and range resolution. Quasi-optical theory and technique recommends a new method for the design of millimeter systems. Application of diffraction elements can contribute to the miniaturization and lightweight of antenna. Research on shaping techniques helps to enhance the performances of antenna. Signals can be transmitted in the shape of focused beam in free space. Quasi-optical technology has the advantages of smaller power loss and more power accoomodation. It is meaningful to study the characteristics of Gauss beam and Bessel beam and their reciprocal transformation.This paper is largely concerned with antenna and beam transformation by using quasi-optical techniques. The main contents are listed as follows:1-Two novel Fresnel diffraction mirror elements, including one order and higher order forms, are proposed. Their characteristics, such as relative bandwidth and diffraction efficiency, have been analyzed and compared by using 2D-FDTD method, respectively.2?Two diffraction monopulse Cassegrain antennas have been constructed by using Fresnel diffraction mirror elements.New waveguide magic-T and relevant sum-difference network has been designed to connect with back-end circuit conveniently. These antennas have been designed, manufactured and tested.3?Two ring-focus dual-reflector antenna configurations are introduced, including the ring-focus Cassegrain antenna and ring-focus Gregorian antenna. Improved coupling magic-Ts and relevant sum-difference networks have also been used in the monopulse antenna system. Theses antenna have been designed, manufactured and tested.4?Under the condition of central blockage in a circular aperture, Stratton-Chu formula has been used to calculate the radiation pattern when the aperture field amplitude distribution is Parabola type or Taylor type.Shaped Cassegrain and Shaped subzone Cassegrain antenna has been designed using geometrical optics (GO) method and simulated by CST software, which expected radiation patterns can be obtained.5?Using the transverse Hertz vector potentials, vector analyses of linearly and circularly polarized Bessel beams of arbitrary orders are presented. Gauss beam transformation through ellipsoidal reflector is analyzed. Shape of a reflector parameterized by Zernike polynomial expansion is studied. The transformation from Gauss beam to Bessel beam is realized using Zernike polynomial expansion and genetic algorithm (GA).