Multiple-input-multiple-output synthetic aperture radar (MIMO-SAR) technology is an effective scheme to achieve there-dimensional (3-D) imaging in millimeter wave and terahertz band. Compared with the 2-D array, the system complexity and the number of array elements are greatly reduced. In this paper, an efficient image reconstruction algorithm in wavenumber domain based on phase shift migration (PSM) was proposed for MIMO-SAR 3-D real-time imaging application. By decomposing the range-wavenumber based on binomial approximation theory, the PSM operation can be achieved only by matrix multiplication and Fourier transform (FT) algorithm without time-consuming wavenumber accumulation. Proof-of-principle experiments were also carried out in 0.1THz band based on a MIMO-SAR prototype system. Both simulation and experimental results of different targets show that the image quality of the proposed algorithm is comparable to that of back-projection algorithm (BPA). The partial enlarged images of the imaging results validate that compared with the range migration algorithm (RMA) the proposed algorithm can achieve higher reconstruction accuracy with comparable efficiency.

This article proposes a novel method for eliminating the first grating lobe of wideband MIMO millimeter-wave imaging array. It exploits the position shift phenomenon of the first grating lobe and can achieve grating lobes suppression without additional calculation. The far-field formula for the first grating lobe is derived and the cause of its shift phenomenon in both azimuth- and range-direction is analyzed. The proposed multi-apodization (MA) method can be used to cut off the part of the shifted grating lobes while maintaining the resolution. However, non-sparse targets still have the far-field residual grating lobes after MA. To solve the problem, the position formula and detailed derivation of the residual grating lobes is given. Therefore, a pixel search (PS) method can be used to remove them. The proposed MA can also be utilized to suppressed the residual grating lobes of the near-field MIMO array. Both simulated and experimental data in different system regimes and frequencies verify its effectiveness.

In this paper, in order to avoid the phenomenon that the diffraction waves cover the incident wave in the reflective frequency-scanning antenna system, which causes insufficient utilization of the beam scanning angular scope, a transmissive planar binary periodical structure metasurface was chosen to achieve frequency-controlled beam scanning, and an approach to realize beam steering with high efficiency was proposed. Specifically, a coherence-enhancing method based on two subcells was proposed to increase conversion efficiency from the incident wave to the diffraction wave. According to the proposed concepts, the frequency scanning antenna based on the transmissive metasurface was designed, fabricated, and measured in the frequency range of 0.25 THz to 0.3 THz. The measured results demonstrate that the designed transmissive metasurface can realize scanning angle 12.5° with comparatively high transferring efficiency. Besides, the proposed transmissive frequency-scanning device also has a lot of unique advantages, such as low cost, simple design and fabrication, which have potential application values in terahertz high frame rate imaging, target detections, communications, etc.

This work proposes a novel terahertz (THz) 3-D imaging system that combines the Gaussian-fan-beam scanning and multiple-input-multiple-output (MIMO) array to create high frame-rate, large field of view (FoV) and high-resolution radar images for continuously non-cooperative on-the-move personnel security screening. The main novelty of the present system is that the 3-D THz focused images of non-cooperative on-the-move whole body can be created in real-time when the persons are illuminated by scanning the MIMO-array-based Gaussian-fan-beam. In this paper, the 3-D image is composed of a serial of 2-D slice images, which are reconstructed by the proposed MIMO-array-based phase shift migration algorithm under the illumination of THz Gaussian-fan-beam. Meanwhile, an analytical expression of the reconstructed point-spread function is derived to provide the theoretical spatial resolutions quantitatively. One prototype imager was designed for the proof-of-principle experiments in 0.2-THz band, and the image reconstruction process is implemented in real-time by the proposed hybrid CPU-GPU solution. At this stage, a FoV of 500 cm×200 cm at 10-m distance costs less than 0.1 second for 3-D imaging during 10 Hz mechanical Gaussian fan-beam scanning. Finally, both simulation and experimental results validate the effectiveness of the proposed imaging algorithm on image reconstruction quality including resolution, frame-rate and FoV.

The real-time capability becomes more and more important for the millimeter-wave imaging systems in variety of applications. To achieve this purpose, the imaging scheme with multiple-input-multiple-output (MIMO) is one of the potential ways, while still limited by the high computational complexity of the conventional MIMO image reconstruction algorithm, which is commonly based on the back-projection theorem. In this letter, an efficient phase shift migration (PSM) image reconstruction algorithm was proposed to improve the computation efficiency for MIMO systems 2-D imaging. By decomposing and approximating the PSM operator reasonably, only complex multiplication and Fourier transform (FT) operations are employed which can be easily carried out to reduce computation cost. An MIMO side-looking prototype system was designed for proof experiments in the 100-GHz band. Although the proposed algorithm introduces a negligible phase error, the experimental results show that the error can be ignored and the algorithm can achieve high-precision real-time imaging.

For the 3-D terahertz (THz) holographic imaging, this work proposes an extended phase-shift migration (PSM) reconstruction algorithm based on multiple-input-multiple-output (MIMO) array with an orthogonal synthetic aperture (SA). For this MIMO-SA-based imaging mechanism, the accurate expression of the signal spatial spectrum can also be obtained by utilizing the method of stationary phase (MSP). Meanwhile, the analytical expression of the reconstructed 3-D point-spread function (PSF) for target under the illumination of MIMO-SA-based THz Gaussian beam is derived to provide the theoretical spatial resolutions quantitatively. A serial of simulation results with fairly good agreement were given to verify the accuracy of the proposed MIMO-SA-based PSM reconstruction algorithm. Meanwhile, due to the PSM’s characteristic of phase shift compensation along the range direction, the image reconstruction process can also be implemented and accelerated by a GPU solution. Finally, two types of MIMO-SA-based prototype imagers are applied for the proof-of-principle experiments. The first prototype imager is configured with one transmitter and two receivers in 0.3-THz band. The MIMO linear array including arbitrary number of transmitters/receivers can be realized by controlling their positions in a low-cost way with the help of the $x$ -axis of a 2-D scanner. The second prototype imager is configured with eight transmitters and eight receivers in 0.2-THz band. The experimental results from the two prototype imagers can validate the effectiveness on image reconstruction quality.