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Design of A Tunable Reflectarray Based on Liquid Crystals for Millimeter-Wave Beam-Forming

Modaber, Aria | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57272 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Ahmadi Boroujeni, Mehdi
  7. Abstract:
  8. Given the increasing need for high-speed wireless links of the 5th and 6th generations, as well as satellite links in millimeter-wave and sub-millimeter-wave bands, the use of reconfigurable intelligent surfaces (RIS) for coverage in both indoor and outdoor spaces is of significant importance. In recent years, the use of tunable arrays through various methods such as optical and electrical has become prevalent. Each of these methods can dynamically control the phase of the reflected wave by influencing the specified characteristics of each element. In this thesis, the design of a liquid crystal-based tunable reflecting array in the millimeter-wave band, for beam shaping with the capability of electrically changing the phase of the reflected wave, is examined. In this project, the decision to use the electrical method is due to its high stability control, insensitivity to environmental characteristics, and ease of implementation. Additionally, discrete grounds for each sub-array are utilized due to the insensitivity of different sub-arrays to their bias states via separate bias paths. The use of liquid crystal as the material in each element, considering its low loss in the millimeter-wave and terahertz bands, can be effective. The structure of each unit cell comprises three main parts: the metallic resonator pattern, the liquid crystal, and the metallic ground. A two-layer structure is used to control the incident wave for both horizontal and vertical polarizations. By applying a DC voltage to each element or sub-array, the orientation of the molecules in the liquid crystal can be changed, causing it to reflect the incident wave like a mirror. When the applied voltage to the liquid crystal exceeds the threshold voltage, it results in a phase shift in the reflected wave. The most desirable state is to achieve a phase difference range of 0 to 360 degrees in the reflected wave, which is accomplished using multi-resonant elements. This has been validated using CST and COMSOL software. Ultimately, by adjusting the phase distribution of all elements in the reflecting array with the specified applied voltages, the desired reflected beam pattern is obtained using MATLAB
  9. Keywords:
  10. Liquid Crystal ; Beamforming ; Beam Shaping ; Tunable Array ; Millimeter Wave ; Fifth Generation of Mobile Networks ; Satellite Link

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