Abstract
Phaseless terahertz coded-aperture imaging (PL-TCAI) is a novel radar computational imaging method that utilizes the coded aperture and the incoherent detector array to achieve forward-looking and high-resolution imaging without relying on relative motion. In this paper, we propose a more reasonable and compact architecture for the PL-TCAI system and derive the imaging model of PL-TCAI based on the random frequency-hopping signal. Since most phase retrieval algorithms for PL-TCAI utilize only the intensity of echo signals to accurately reconstruct the target, excessive measurement samples are usually required. In order to reduce the number of measurement samples required for imaging, this paper proposes a sparse Wirtinger flow algorithm with optimal stepsize (SWFOS) by using the sparse prior of the target. The specific procedures of the SWFOS algorithm include the support recovery, initialization by truncated spectral method, iteration via gradient descent scheme, hard threshold operation, and stepsize optimization of iteration. Numerical simulations are performed, and the results show that the SWFOS algorithm not only has good performance for the PR problem, but can also sharply reduce the number of measurement samples required for imaging in the PL-TCAI system.
Highlights
Terahertz coded-aperture imaging (TCAI) [1,2,3,4] is a novel high-resolution imaging method that does not rely on any relative motion between the radar and the target
Solving the imaging equation can be regarded as a phase retrieval (PR) problem, and in Reference [20], we have proved that the PR algorithm can be adopted to accurately reconstruct the target in Phaseless terahertz coded-aperture imaging (PL-TCAI)
We propose a compact PL-TCAI system configuration based on the combination of the incoherent detector array and the coded aperture, which can achieve fast imaging, high-resolution imaging, and forward-looking imaging without any relative motion
Summary
Terahertz coded-aperture imaging (TCAI) [1,2,3,4] is a novel high-resolution imaging method that does not rely on any relative motion between the radar and the target. For traditional TCAI with coherent receivers, high frequency and wide bandwidth signals are beneficial for improving imaging resolution. The proposed SWFOS algorithm can utilize the sparse priori of the target to effectively reduce the number of measurement samples required in PL-TCAI, significantly reduce the number of coding and sampling, and further improve the imaging speed. For the SPARTA, SWF, and Thresholding Wirtinger Flow algorithms, the stepsizes are selected empirically, and the default stepsize functions or stepsize constants are proposed for the measurement vectors that conform to the standard Gaussian random distribution [26,27,28,29,30,31,32,33,34,35].
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