Abstract
Computational imaging using coded apertures offers all-electronic operation with a substantially reduced hardware complexity for data acquisition. At the core of this technique is the single-pixel coded aperture modality, which produces spatio-temporarily varying, quasi-random bases to encode the back-scattered radar data replacing the conventional pixel-by-pixel raster scanning requirement of conventional imaging techniques. For a frequency-diverse computational imaging radar, the coded aperture is of significant importance, governing key imaging metrics such as the orthogonality of the information encoded from the scene as the frequency is swept, and hence the conditioning of the imaging problem, directly impacting the fidelity of the reconstructed images. In this paper, we present dielectric lens loading of coded apertures as an effective way to increase the information coding capacity of frequency-diverse antennas for computational imaging problems. We show that by lens loading the coded aperture for the presented imaging problem, the number of effective measurement modes can be increased by 32% while the conditioning of the imaging problem is improved by a factor of greater than two times.
Highlights
We have presented a lens-loading technique to increase the orthogonality of the measurement modes radiated by a frequency-diverse cavity-backed metasurface antenna at X-band frequencies
It has been shown that the image reconstructed using the lens-loaded cavity exhibits a substantially improved fidelity in comparison to the image reconstructed without the lens
To quantitatively analyse the underlying reason behind this improvement, we have studied the singular value spectrum of the considered imaging problem and showed that the lens loading of the metasurface antenna flattens the singular value decomposition (SVD) spectrum, reducing the amount of correlation between the information encoded at adjacent frequency points within the selected operating frequency band
Summary
Imaging and sensing systems leveraging various microwave radar modalities have been the subject of much research with a variety of applications from remote sensing [1,2,3,4,5,6,7,8] to biomedical imaging [9,10,11,12,13,14,15] and security-screening [16,17,18,19,20,21,22] to name a few. Mechanical raster scanning suggests moving the antenna across multiple spatial sampling points separated by a distance of λ/2, where λ is the wavelength at the operating frequency This approach relying on pixel-by-pixel raster scanning the imaged scene can substantially increase the data acquisition time, especially for applications requiring to synthesise electrically large apertures. Whereas the all-electronic operation of the phased array apertures can substantially improve the data acquisition speed, limitations to this technique persist. In this approach, each antenna element within the synthesised array aperture requires a dedicated phase shifting circuit to achieve a coherent phase response across the aperture to raster scan the radiation pattern of the array in an all-electronic manner. As a result, phased array radars, albeit exhibiting all-electronic operation, typically have a substantially complex hardware architecture and can consume a large amount of power
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