Sampling Deviation Real-time Calibration Method for Wideband Simulator

Hardware-in-the-loop simulation is an efficient method for research on radar system.Target’s echo which offered by the simulator should be synchronized with radar on frequency, time, and range bin. However, because simulator needs to take into account of the requirements of various types of radar, it is difficult to make the clock of simulator synchronized with the clock of radar. To solve the problem, synchronous sampling deviation model is established. Influence of sampling deviation on imaging is analyzed. An engineering method is put forward to eliminate the sampling deviation. This method not only provides a reference for simulation system, but also provides a reference for the design of radar system

Hardware-in-the-loop simulation technology of wide-band radar targets based on scattering center model

AbstractHardware-in-the-loop (HWIL) simulation technology can verify and evaluate the radar by simulating the radio frequency environment in an anechoic chamber. The HWIL simulation technology of wide-band radar targets can accurately generate wide-band radar target echo which stands for the radar target scattering characteristics and pulse modulation of radar transmitting signal. This paper analyzes the wide-band radar target scattering properties first. Since the responses of target are composed of many separate scattering centers, the target scattering characteristic is restructured by scattering centers model. Based on the scattering centers model of wide-band radar target, the wide-band radar target echo modeling and the simulation method are discussed. The wide-band radar target echo is reconstructed in real-time by convoluting the transmitting signal to the target scattering parameters. Using the digital radio frequency memory (DRFM) system, the HWIL simulation of wide-band radar target echo with high accuracy can be actualized. A typical wide-band radar target simulation is taken to demonstrate the preferable simulation effect of the reconstruction method of wide-band radar target echo. Finally, the radar target time-domain echo and high-resolution range profile (HRRP) are given. The results show that the HWIL simulation gives a high-resolution range distribution of wide-band radar target scattering centers

A Fast Real-Time Calculation Method for SAR Echo History

Aiming at the problem that the simulation calculation of synthetic aperture radar (SAR) target echo is too large, two multi-order Taylor series expansions are used to calculate the distance history in the echo system function, and the fast real-time calculation of the distance history is completed by combining the data extrapolation method. This method uses multiple multiplications and additions instead of square root operation with large amount of calculation, which can ensure the real-time performance of distance calculation under the premi-se of certain calculation accuracy. At the same time, combined with the regularity of distance history model, data extrapolation is used instead of repeated calculation process to further reduce the amount of calculation and improve real-time performance. By comparing the calculation error of different orders of Taylor series expansion at the same distance, the fourth order is the optimal Taylor expansion order under this simulation condition. Finally, the echo simulation and imaging of 9 densely distributed point targets and real scene targets are carried out respectively. The point target simulation results show that the method can reduce the time of generating echo signal by 53 % and increase the speed by 2 times without affecting the performance of echo signal. The real scene simulation results show that the method can be applied to the echo simulation of large scenes

Research on a forward‐looking scanning imaging algorithm for a high‐speed radar platform

Abstract The range and azimuth information of a target can be obtained after coherent pulse accumulation of the traditional multiframe stepped‐frequency (SF) synthesis wideband echo and spectrum analysis, and high‐resolution two‐dimensional imaging of the target can be achieved. However, the accumulation of a certain number of pulses requires a long beam dwell time, which cannot meet real‐time imaging requirements for high‐speed radar moving platforms. To solve the above problems, a scanning imaging mode is proposed by combining forward‐looking imaging and scanning imaging, and a target echo signal model with the structure of scanning stepped‐frequency is constructed. The SF pulses are grouped and transmitted according to the scanning order, and the echo pulses are sorted and reorganised. After the timing compensation and range Doppler coupling compensation are completed, the target is located and projected. The proposed imaging mode can achieve high‐resolution scanning forward‐looking imaging and can basically attain an azimuth resolution of approximately 0.1° within the forward‐looking scanning range. This imaging mode has higher real‐time performance and a larger target imaging range than the traditional methods. Moreover, the simulation results showed good performance via the scanning imaging method

Joint Sensor Selection and Power Allocation Algorithm for Multiple-Target Tracking of Unmanned Cluster Based on Fuzzy Logic Reasoning

The unmanned aerial vehicle (UAV) cluster is gradually attracting more attention, which takes advantage over a traditional single manned platform. Because the size of the UAV platform limits the transmitting power of its own radar, how to reduce the transmitting power while meeting the detection accuracy is necessary. Aim at multiple-target tracking (MTT), a joint radar node selection and power allocation algorithm for radar networks is proposed. The algorithm first uses fuzzy logic reasoning (FLR) to obtain the priority of targets to radars, and designs a radar clustering algorithm based on the priority to form several subradar networks. The radar clustering algorithm simplifies the problem of multiple-radar tracking multiple-target into several problems of multiple-radar tracking a single target, which avoids complex calculations caused by multiple variables in the objective function of joint radar node selection and power allocation model. Considering the uncertainty of the target RCS in practice, the chance-constraint programming (CCP) is used to balance power resource and tracking accuracy. Through the joint radar node selection and power allocation algorithm, the radar networks can use less power resource to achieve a given tracking performance, which is more suitable for working on drone platforms. Finally, the simulation proves the effectiveness of the algorithm

City Branding Evaluation as a Tool for Sustainable Urban Growth: A Framework and Lessons from the Yangtze River Delta Region

With the rising tide of globalization, urban branding campaigns have become the focal points of decision makers and planners aiming to establish city reputations and to achieve long-term urban prosperity. This paper, therefore, aims to develop a sustainability-oriented city branding framework that incorporates (1) comprehensive perceptions from various stakeholders through questionnaires and (2) empirical applications that evaluate the city-level potentials for a global mega-region in support of its sustainable growth. Seven major aspects, i.e., economic development, environment, potential, pulse, people, infrastructure, and governance, have been identified and assessed in the context of 26 prefecture cities in the Yangtze River Delta region. Moreover, a cluster analysis differentiated these cities into four groups with distinct characteristics and development paths. Through the framework and evaluation outputs, local planners, researchers, and decision-makers would be better placed to design and implement sustainable policy packages and incentives, with a quantitative insight into current strengths and weaknesses

A Novel NADP(H)-Dependent 7alpha-HSDH: Discovery and Construction of Substrate Selectivity Mutant by C-Terminal Truncation

7α-Hydroxysteroid dehydrogenase (7α-HSDH) plays an important role in the biosynthesis of tauroursodeoxycholic acid (TUDCA) using complex substrate chicken bile powder as raw material. However, chicken bile powder contains 4.74% taurocholic acid (TCA), and a new by-product tauroursocholic acid (TUCA) will be produced, having the risk of causing colorectal cancer. Here, we obtained a novel NADP(H)-dependent 7α-HSDH with good thermostability from Ursus thibetanus gut microbiota (named St-2-2). St-2-2 could catalyze taurochenodeoxycholic acid (TCDCA) and TCA with the catalytic activity of 128.13 and 269.39 U/mg, respectively. Interestingly, by a structure-based C-terminal truncation strategy, St-2-2△C10 only remained catalytic activity on TCDCA (14.19 U/mg) and had no activity on TCA. As a result, it can selectively catalyze TCDCA in waste chicken bile powder. MD simulation and structural analysis indicated that enhanced surface hydrophilicity and improved C-terminal rigidity affected the entry and exit of substrates. Hydrogen bond interactions between different subunits and interaction changes in Phe249 of the C-terminal loop inverted the substrate catalytic activity. This is the first report on substrate selectivity of 7α-HSDH by C-terminal truncation strategy and it can be extended to other 7α-HSDHs (J-1-1, S1-a-1)