Research On Free-space Coupling Of Terahertz Feed And Antenna System Based On Quasi-optical Technology

Terahertz quasi-optical feed and antenna system is an important part of the terahertz wireless system. As a key technology, the free-space coupling of the terahertz quasi-optical system has gained increasing attention. Based on the demands of terahertz imaging, this thesis researched on the feeds and quasi-optical focusing elements. We studied linear and circular polarized feeds respectively under different practical requirements and processing techniques. As for the focusing elements, a design based on Gaussian beam transformation is given to validate the accuracy of Gaussian beam theory. The main research content is as follows:1.The design and implementation of the feeds:(1) A series of linear polarized multi-mode metal horn feeds with realized gains of 15/20/30 dB were designed. Frequency of these feeds ranges from 220 GHz to 500 GHz. Parameters were analyzed to form a symmetrical radiation pattern with high Gaussian efficiency. We tested the VSWR and gains of our feeds at the frequency of 220 GHz. The simulations coincided with the measurements, indicating that the feeds are good alternatives to imported ones.(2) A circular polarized antenna integrated with the planar corrugations in the light of MEMS technology was proposed. The design achieved circular polarization and a high gain under two-dimensional low profile conditions. The optimization showed that the planar corrugations can efficiently improve the gain of the antenna. Meanwhile, the optimization also showed that the axial ratio can be improved via changing the angle between waveguide-fed and the circular polarizer. We processed and tested the antenna at Ka and THz frequency. The experimental results agreed well with simulation, which revealed the validity of our design and illustrated that the MEMS technique meets the requirements of THz new antenna.2. The design of the coupling of THz feeds and quasi-optical focusing elements: A solution to free-space coupling between the feeds and the focusing elements was presented on the base of the Gaussian beam transformation theory. The research showed that the Gaussian beam can be adjusted and controlled by optimizing the curvature of illuminated and dark sides of the lens which are sensitive to the beam waist. A THz dielectric hyperboloid lens antenna with different curvatures was designed. Afterwards, a quasi-optical feed and antenna system employing the feed and lens above-mentioned was built and simulated to verify the availability and reasonableness of the solution.