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Beam Shaping by Meta-surfaces in Millimeter-Wave Active Standoff Imaging

Imanbeigi, Ehsan | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56115 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Ahmadi Boroujeni, Mehdi
  7. Abstract:
  8. Beam shaping, the transformation of radiated Gaussian beam from the millimeter wave source (conical horn antenna) into a flat-top beam at a certain distance, in the Millimeter wave active stand-off imaging system can be done in different ways, among them, beam shaping with a concave-convex lens (double-sided lens) in transmission mode (previous research done) can be mentioned. This lens consists of a convex-plane and a plane-concave lenses. when the electromagnetic wave passes through the convex-plane part, the wave front of the incident electric field changes from spherical to plane so that the divergent incident rays become parallel, and then the phase profile of the electric field changes by passing through the Plane-concave part so that the beam intensity changes from Gaussian to uniform at a certain distance from it. In this research, we want to use a simple method to obtain a phase profile that parallelizes and shapes the rays at the same time. In this approach, the obtained phase profile is a combination of the beam shaping phase profile and the optical path difference compensating phase profile. We will use the geometrical transformation technique to obtain the beam shaping phase profile and Fermat's principle to obtain the compensating phase profile. To validate the proposed method, we will first convert a double-sided lens into a one-sided (plano-convex lens) using the thin element approximation and the proposed method. Then, using the presented method, we will replace the double-sided lens with a metal layer placed on a thin substrate with low dielectric loss (Meta-lens), which can be implemented with lithography, to create a flat -top beam intensity in reflection mode. To design the meta- lens structure, we will first design a resonator that is insensitive to the polarization of the incident wave (parallel or vertical) and by changing its dimensions, it is possible to shift the phase of the linear polarized incident wave (polarization of Horn antenna is linear) from zero to 360 degrees. we will determine the dimensions of the resonators according to the proposed phase profile, and finally, by placing the resonators with a specific period next to each other on a square shaped surface, the metal-lens structure will be achieved. We will simulate the output beam intensity of meta-lens in two scenarios of axial and off-axis radiation of the horn antenna using COMSOL software. Simple manufacturing, compactness, low loss, insensitive to polarization, parallelization and beam shaping at the same time with only one surface and the possibility of using it in lower frequency bands are among the advantages of meta-lens
  9. Keywords:
  10. Beam Shaping ; Metasurfaces ; Stand-Off Imaging ; Millimeter-Wave Imaging ; COMSOL Software

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