542 research outputs found
Computational polarimetric microwave imaging
We propose a polarimetric microwave imaging technique that exploits recent
advances in computational imaging. We utilize a frequency-diverse cavity-backed
metasurface, allowing us to demonstrate high-resolution polarimetric imaging
using a single transceiver and frequency sweep over the operational microwave
bandwidth. The frequency-diverse metasurface imager greatly simplifies the
system architecture compared with active arrays and other conventional
microwave imaging approaches. We further develop the theoretical framework for
computational polarimetric imaging and validate the approach experimentally
using a multi-modal leaky cavity. The scalar approximation for the interaction
between the radiated waves and the target---often applied in microwave
computational imaging schemes---is thus extended to retrieve the susceptibility
tensors, and hence providing additional information about the targets.
Computational polarimetry has relevance for existing systems in the field that
extract polarimetric imagery, and particular for ground observation. A growing
number of short-range microwave imaging applications can also notably benefit
from computational polarimetry, particularly for imaging objects that are
difficult to reconstruct when assuming scalar estimations.Comment: 17 pages, 15 figure
2-D Coherence Factor for Sidelobe and Ghost Suppressions in Radar Imaging
The coherence factor (CF) is defined as the ratio of coherent power to
incoherent power received by the radar aperture. The incoherent power is
computed by the multi-antenna receiver based on only the spatial variable. In
this respect, it is a one-dimensional (1-D) CF, and thereby the image sidelobes
in down-range cannot be effectively suppressed. We propose a two-dimensional
(2-D) CF by supplementing the 1-D CF by an incoherent sum dealing with the
frequency dimension. In essence, we employ both spatial diversity and frequency
diversity which, respectively, enhance imaging quality in cross range and
range. Simulations and experimental results are provided to demonstrate the
performance advantages of the proposed approach.Comment: 7 pages, 21 figure
Enhancing Near-Field Sensing and Communications with Sparse Arrays: Potentials, Challenges, and Emerging Trends
As a promising technique, extremely large-scale (XL)-arrays offer potential
solutions for overcoming the severe path loss in millimeter-wave (mmWave) and
TeraHertz (THz) channels, crucial for enabling 6G. Nevertheless, XL-arrays
introduce deviations in electromagnetic propagation compared to traditional
arrays, fundamentally challenging the assumption with the planar-wave model.
Instead, it ushers in the spherical-wave (SW) model to accurately represent the
near-field propagation characteristics, significantly increasing signal
processing complexity. Fortunately, the SW model shows remarkable benefits on
sensing and communications (S\&C), e.g., improving communication multiplexing
capability, spatial resolution, and degrees of freedom. In this context, this
article first overviews hardware/algorithm challenges, fundamental potentials,
promising applications of near-field S\&C enabled by XL-arrays. To overcome the
limitations of existing XL-arrays with dense uniform array layouts and improve
S\&C applications, we introduce sparse arrays (SAs). Exploring their potential,
we propose XL-SAs for mmWave/THz systems using multi-subarray designs. Finally,
several applications, challenges and resarch directions are identified
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