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The Effect of Antenna Arrangement on the Aliasing Artifacts in Multi-Static Millimeter Wave Imaging Systems Based on the K-Space Analysis and Signal Processing

Kazemi, Mahmoud | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55984 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Shabany, Mahdi; Kavehvash, Zahra
  7. Abstract:
  8. Millimeter wave imaging has been used in many applications including security screening and medical imaging. Millimeter wave screening systems are considered a reliable option in the design of surveillance systems, because they feature enough penetration in dielectric materials including clothes, low health- risk and decent resolution. The first generation of such systems are based on mono-static arrays and mechanical scanning. Large mono-static arrays are challenging and expensive to implement, because they require high number of antenna elements to satisfy the Nyquist sampling rate. Moreover, the minimum sampling rate imposes limitations on design and size of antenna elements. So, mono-static arrays require mechanical scanning to overcome such challenges. Nevertheless, the high scanning time makes it impossible to design real-time imaging systems that does not impede the passenger flow. Consequently, sparse multi-static arrays featuring fewer antennas, are used to design millimeter-wave imaging systems. The existing framework to design and analysis of multi-static arrays is based on the approximation of them with an equivalent monostatic array. It has been shown that this approximation is not a comprehensive representative of the original array and especially fails to describe the aliasing artifacts of multi-static arrays. In this thesis, we derive the theory required to analyze the aliasing behavior of multi-static arrays. The provided simulations and experiment show that our analysis can locate aliasing artifacts with less than two degrees of error. Then we have studied the level of aliasing artifacts and explained why some aliasing artifacts are more apparent than the others based on the k-space analysis. Considering different scenarios, multiple simulations are performed to validate it. The results show that our analysis can well qualitatively (visible or not visible) predict the level of aliasing artifacts. Afterwards, we discuss how to deal with aliasing artifacts. We focus on the non-uniform sampling theorem and analyze the requirements of non-uniform placement of antennas in multi-static millimeter-wave imaging systems based on the k-space analysis to suppress the aliasing artifacts while keeping the imaging quality. Simulations and an experiment are performed that show that the proposed non-uniform arrangement of antennas can reduce the level of aliasing artifacts by around 3dB with respect to the corresponding uniform arrangements with negligible impacts on the imaging quality
  9. Keywords:
  10. Millimeter Wave ; Millimeter-Wave Imaging ; Multistatic Imaging ; Image Aliasing ; Array Design ; Spatial Fourier ; Antenna Placement

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