Millimeter-wave spotlight imager using dynamic holographic metasurface antennas

Abstract

Computational imaging systems leverage generalized measurements to produce high-fidelity images, enabling novel and often lower cost hardware platforms at the expense of increased processing. However, obtaining full resolution images across a large field-of-view (FOV) can lead to slow reconstruction times, limiting system performance where faster frame rates are desired. In many imaging scenarios, the highest resolution is needed only in smaller subdomains of interest within a scene, suggesting an aperture supporting multiple modalities of image capture with different resolutions can provide a path to system optimization. We explore this concept in the context of millimeter-wave imaging, presenting the design and simulation of a single frequency (75 GHz), multistatic, holographic spotlight aperture integrated into a K-band (17.5-26.5 GHz), frequency-diverse imager. The spotlight aperture - synthesized using an array of dynamically tuned, holographic, metasurface antennas - illuminates a constrained region-of-interest (ROI) identified from a low-resolution image, extracting a high-fidelity image of the constrained-ROI with a minimum number of measurement modes. The designs of both the static, frequency-diverse sub-aperture and the integrated dynamic spotlight aperture are evaluated using simulation techniques developed for large-scale synthetic apertures.

Low-Profile Metamaterial-Based Adaptative Beamforming Techniques

“…Combining the holography concept with the reconfigurable metasurface will further allow dynamic beamsteering capabilities, without the need of mechanical moving parts [49][50][51][52][53][54][55][56][57]. In 2013, the Kymeta Corporation has demonstrated an active metasurface antenna used for bi-directional high-speed internet connectivity [49].…”

Sparsity-Driven Reconstruction Technique for Microwave/Millimeter-Wave Computational Imaging

“…This attribute partly responds to the problem of reconstructing space-frequency signals in the radiating aperture from a limited number of measured frequency information. The second constraint that needs to be addressed is the replacement of this extremely simple yet inefficient equalization operation with a matrix approach that can be solved by means of various pseudo-inversion techniques, which may be direct such as the Tikhonov regularization [ 12 ] or the truncated singular value decomposition [ 23 ], or iterative such as least squares-based techniques [ 16 , 30 ] or the generalized minimal residual method [ 17 , 31 ]. Using the sparsity properties illustrated above, this reconstruction is carried out in the time domain, working on the expression of the measured signal according to those received in the radiating aperture, filtered by propagation in the computational imaging component.…”

“…The constraint is thus pushed back into the digital layer where the formulation and resolution of inverse problems represent new challenges that can make these solutions competitive. It has been demonstrated that such systems can be based on the use of electrically large cavities connected to conventional antenna arrays [ 11 , 12 , 13 ], on the use of metasurfaces encoding information directly in the radiating aperture [ 14 , 15 , 16 ], or even on hybrid solutions of leaky cavities that demonstrate interesting performance in many imaging modalities [ 17 , 18 , 19 ]. Connections can also be made with earlier systems based on the use of frequency scanning antennas whose radiation patterns can encode a sum of information relative to the position of a target into a reduced number of signals [ 20 , 21 , 22 ].…”

3D Conductive Polymer Printed Metasurface Antenna for Fresnel Focusing

“…The concept of Fresnel focusing enables the antenna radiated fields to be focused at a defined spot in the Fresnel region of the antenna, leading to increased field intensities at the focused region. This capability has been shown to hold significant potential in several emerging applications, such as near-field imaging [7], non-destructive testing [8], and wireless power transfer [9].…”