The smart unmanned aerial vehicle (UAV) with a mini-SAR payload provides an advanced earth observation capability for target detection and imaging. Simiar to large-scale SAR, mini-SAR also has an increasing requirement for high resolution and wide swath. However, due to the low cruising altitude of UAVs, small coverage angles in the direction range, and the insufficient operating range of mini-SAR, expanding the swath has become an urgent problem for mini-SAR. To solve this problem, this paper proposes a W-Band active phased array miniaturized SAR (APA mini-SAR), whose scanning capacity has been proven on the multi-rotor UAV platform. Many efforts, including the novel active phased array antenna scheme, the sparse triangular arrangement of antenna elements, the wideband chirp source, and the three-dimensional integration technology, have been made to develop this APA mini-SAR for the first time in the W-Band. The volume of this APA mini-SAR is 69 × 82 × 87 mm³, with a weight of 600 g. Combined with a new motion compensation strategy and the ω-k imaging algorithm, the focused image is finally obtained. Experiments have been conducted, and the results indicate that this APA mini-SAR has a resolution of 4.5 cm, the imaging swath is three times that of the traditional single-channel mini-SAR, and the operating range is increased to 800 m.

The fast developed and widely used radar system techniques call for novel solutions on hardware design. Under a massive data source and the real-time requirements in radar signal processing scenarios (e.g., Synthetic Aperture Radar (SAR)), reconfigurable dataflow architecture is considered as a promising solution. In this article, we first extract the typical algorithms in radar systems and characterize their dataflow manners. Then a reconfigurable dataflow architecture is proposed, with high width SIMD extended PE. The application implementations with mapping strategy and workflow are shown to reach high hardware utilization and efficient data supply. Our work achieves $8 \times$ and $5.3\times$ energy efficiency improvement over DSP and GPU (NVIDIA Tesla V100), respectively, on large scale FFT, as well as high performance. Under actual scene of $8K \times 8K$ SAR imaging baseline, it gets $9.4 \times$ speedup over a six-core CPU.

Frequency modulation continuous wave (FMCW) synthetic aperture ladar (SAL) system can support the generation and processing of large bandwidth signals, which has strong capabilities in target detection, description and identification. However, frequency modulation nonlinearity of the transmitted signal has become a bottleneck problem that restricts the high-resolution ranging of FMCW SAL. This letter establishes an echo model with nonlinearity, and proposes a nonlinear phase estimation and compensation method based on Wigner-Ville distribution (WVD) with gradient rotation enhancement. Firstly, we establish the nonlinearity model of the internal calibration signal in time-frequency (TF) domain, and use WVD to calculate the time-frequency distribution (TFD). Secondly, the TFD is enhanced by rotating gradient vector, which also can eliminate noises and false components in the TFD. Then, the nonlinear phase of the transmitted signal is estimated by establishing a nonlinearity model in the TF domain. Finally, the residual video phase (RVP) filtering is introduced to eliminate the range-dependent nonlinearity and achieve nonlinearity correction of echoes at any range. Experiments and real data tests show that the method proposed in this letter can accurately estimate and correct the nonlinearity of the dechirp signal, which effectively improves the range resolution of FMCW SAL.

Radio frequency tag detection by radars has received much attention in recent years for its long working distance and high positioning accuracy. This study proposes a novel method that combines synthetic aperture radar (SAR) system with metamaterial-modulated tags that can simultaneously achieve tag positioning and imaging. However, the high working frequency of SAR and the noncoherence between SAR and tag signals pose great challenges to the design and focused imaging of tag. Based on the mathematical model establishment of modulated target imaging, a new transmission waveform strategy and signal processing method were developed for simultaneous focused imaging of scenes and tag that were verified through simulation. Meanwhile, a tag-designing method based on metamaterial modulation was proposed, and direct loading of modulation signals onto radar echoes in the millimeter-wave band was realized. Additionally, an experimental system based on vehicle-mounted miniaturized SAR (Mini-SAR) and metamaterial tag was established. The experimental results indicated that focused images of the tag and environment were simultaneously obtained, and the SAR system realized long-distance, accurate detection, and positioning of the tag, with a working distance of 300 m, a range resolution of 27 cm, an azimuth resolution of 18 cm, and a positioning accuracy of 1.5 cm.

Synthetic Aperture Ladar (SAL) is a sensor that combines laser detection technology with synthetic aperture technology to achieve ultra-high-resolution imaging. Due to its extremely short wavelength, SAL is more sensitive to motion errors. The micrometer-level motion will affect the target’s azimuth focus. This article proposes an SAL motion compensation method based on Symmetric Triangular Linear Frequency Modulation Continuous Wave (STLFMCW) segmented interference, utilizing the characteristics of a triangular wave, to solve the problem of target azimuth defocusing. This article first establishes an STLFMCW echo signal model based on the SAL system under the influence of motion errors. Secondly, the radial velocity gradient along the azimuth direction is extracted using the triangular-wave-positive and -negative frequency modulation signals segmented interference method. Then, for the initial phase wrapping problem, the frequency spectral cross-correlation method is used to accurately estimate the initial radial velocity error. The radial velocity gradient is integrated along the azimuth to obtain the platform motion trajectory. Finally, the compensation functions are constructed to complete the echo Range Cell Migration (RCM) correction and residual phase compensation, resulting in a focused SAL image. This article verifies the practical effect of this method in eliminating motion errors using only one-period STLFMCW signal through simulation and real experiments. The quantitative results show that compared with the traditional method, the proposed method reduces the azimuth Peak Sidelobe Ratio (PSLR) by 8dB and the Integrated Sidelobe Ratio (ISLR) by 9 dB. This method has significant improvements and is of great significance for high-resolution FMCW SAL imaging.

In order to expand the applications of the traditional Vivaldi antenna by addressing the low gain of the traditional Vivaldi antenna, this paper combines the phase distribution of the Vivaldi antenna aperture based on the analysis of the transmission characteristics of a dielectric unit by utilizing the advantages of artificial electromagnetic material. A more reasonable method of loading a dielectric lens is proposed and utilized in combination with edge grooving. A comparison of the results shows that the antenna operates in the frequency range of 4 to 16 GHz. The low-frequency boost is approximately 3 dB, and the high-frequency boost is approximately 9.6 dB.