Ultra-wide band gap and wave attenuation mechanism of a novel star-shaped chiral metamaterial

A novel hollow star-shaped chiral metamaterial(SCM)is proposed by incorporating chiral structural properties into the standard hollow star-shaped metamaterial,exhibiting a wide band gap over 1500 Hz.To broaden the band gap,solid single-phase and two-phase SCMs are designed and simulated,which produce two ultra-wide band gaps(approximately 5116 Hz and 6027 Hz,respectively).The main reason for the formation of the ultra-wide band gap is that the rotational vibration of the concave star of two novel SCMs drains the energy of an elastic wave.The impacts of the concave angle of a single-phase SCM and the resonator radius of a two-phase SCM on the band gaps are studied.Decreasing the concave angle leads to an increase in the width of the widest band gap,and the width of the widest band gap increases as the resonator radius of the two-phase SCM increases.Additionally,the study on elastic wave propagation characteristics involves analyzing frequency dispersion surfaces,wave propagation directions,group velocities,and phase velocities.Ultimately,the analysis focuses on the transmission properties of finite periodic structures.The solid single-phase SCM achieves a maximum vibration attenuation over 800,while the width of the band gap is smaller than that of the two-phase SCM.Both metamaterials exhibit high vibration attenuation capabilities,which can be used in wideband vibration reduction to satisfy the requirement of ultra-wide frequencies.

Compact Coplanar Epsilon-Negative Antenna with Ultra-Wide Band Character

In this paper, a compact coplanar epsilon.negative(ENG) antenna is proposed with ultra.wide operation band and small size of 18×11.5 mm2. The proposed antenna is designed based on a coplanar.waveguide(CPW) feeding antenna, and thus the via.free structure is employed to realize the ENG unit cell, which is convenient to tune the frequency of zeroth.order resonance(ZOR) and extends the ZOR bandwidth. The high.order resonant frequencies are achieved and mainly determined by the separate slots that are located between the radiating patch and the ground plane. Adding the left.handed inductance between the radiating patch and ground has slight impact on the high.order resonant frequencies, and then the ultra.wide band is achieved by merging the ZOR bandwidth with the high.order resonant bandwidths. The ground plane primarily works as a matching network for the proposed antenna. Although it generates a low.frequency resonance, the performance is undesirable due to the impedance mismatching. The measured results show that the reflection coefficient, |S11| <.10 d B, is in a wide frequency range from 5.25 to 13 GHz, which covers the upper operation band of UWB communication. Also, the antenna contains relatively stable gains and omni.directional radiation patterns.

ON THE PAR REDUCTION OF MB-OFDM ULTRA-WIDEBAND SIGNALS

The Peak to Average power Ratio (PAR) of a Multi-Band Orthogonal Frequency-Division Multiplexing (MB-OFDM) Ultra-Wide Band (UWB) signals can be substantially larger than that of single carrier or carrier-less ultra-wideband signals. In this letter, a novel PAR reduction scheme for the MB-OFDM UWB system based on spreading and interleaving is proposed. By spreading the coded bits over each subcarrier in corresponding band and interleaving the spread symbols across all bands, the PAR statistics of the MB-OFDM signals can be improved and the PAR is reduced obviously. In the PAR reduction scheme, there is no loss in transmission data rate or Bit Error Rate (BER) performance decreasing. Since the spreading and interleaving operation are implemented by unitary Hadamard sequences and used for an approach to provide the robustness of the UWB system to narrowband interference, there is no additional implementation burden. Simulation results show that the investigated scheme gives the PAR reduction of 3dB compared with that of the original MB-OFDM signals.

Numerical simulation of the coupling of ultra-wide band electromagnetic pulse into landmine by aperture

The modern landmine＇s electronic fuse is susceptible to strong interference or can even be damaged by the ultra-wide band electromagnetic pulse（UWB-EMP）. The finite-difference time-domain（FDTD） method in lossy media with cylindrical coordinates is used to study the interactions of the UWB-EMP with the landmine. First, the coupling of UWB-EMP into the landmine shielding shell through an aperture is numerically simulated. Second, the coupled electromagnetic field of mine shells made of different shielding materials and with apertures of different sizes is plotted. Third, the aperture coupling laws of UWB-EMP into shells are analyzed and categorized. Such an algorithm is capable of effectively preventing ladder similar errors, and consequently improving the calculation precision, and in addition to adopting the message passing interface（MPI） parallel method to divide the total calculating range into more sub-ranges, the overall calculating efficiency is greatly increased. These calculations are surely a constructive reference for modern landmine design against electromagnetic damage.

Mobile Robot Positioning and Tracking Based on Ultra-wideband Technology

To solve the precision self-positioning problem for mobile robot,a positioning program based on ultra-wideband technology was proposed. Ultra-wideband pulse has very high bandwidth; ranging accuracy can achieve centimeter-level theoretically. The mobile robot obtained the distance to the reference node by sending ultra-wideband pulse. According to the geometric relations among the references and the robot,establish equations to calculate the position coordinates. Then Kalman filter algorithm was applied for mobile robot tracking. Simulation results show that robot positioning and tracking based on ultra-wideband technology can achieve indoor and outdoor seamless docking.

Designing a Carbon Nanotube Field-Effect Transistor with High Transition Frequency for Ultra-Wideband Application

Theoretical calculations predict transition frequencies in the terahertz range for the field-effect transistors based on carbon nanotubes, and this shows their suitability for being used in high frequency applications. In this paper, we have designed a field-effect transistor based on carbon nanotube with high transition frequency suitable for ultra-wide band applications. We did this by optimizing nanotube diameter, gate insulator thickness and dielectric constant. As a result, we achieved the transition frequency about 7.45 THz. The environment of open source software FETToy is used to simulate the device. Also a suitable model for calculating the transition frequency is presented.

Evaluation of System Performance of Ultra-Wide Band Jointing in MC Signaling in Correlated Environments

The evaluation of System Performance of UWB (ultra-wide band) jointing in MC (multi-carrier) signaling in correlated environments is presented in the report. The correlated Nakagami-m statistical distribution for the multipath fading model is assumed in this scenario. In fact to establish the model for analyzing in this article is using MC-CDMA (multi-carrier code-division multiple-access) system characterization combined with a UWB scheme. The average BER (bit error rate) is calculated and compared to a special case of previously published results. Studied results from this paper can be implied to approve the system performance for a UWB system combined with a MC-CDMA wireless communication system. It is worth noting that the Nakagami-m distributed fading parameter significantly dominates UWB system performance when it cooperates with MC signaling under a fading environment. Finally, it is worthy of noting that when the SNR (signal-to-noise ratio) at system’s receiver reaches a preset high threshold value, the parameter of power decay ratio effect could be not included.

基于X波段SAR雷达成像算法研究

成像算法对于SAR成像雷达的最终结果有着决定性作用,论文基于X波段的SAR成像雷达基础上,对成像算法的理论进行研究,讨论了成像算法的SAR空间分辨率和多普勒频移,重点分析了成像算法中距离向处理问题、距离徙动处理问题以及方位向处理问题。利用X波段SAR雷达进行了5m具体实物成像结果测试。结果表明:SAR雷达的距离向分辨率和方位向分辨率对雷达成像精度的影响很大;SAR雷达在正侧视的成像精度明显较好,在15°角斜侧视的成像结果不如正侧效果。这是由成像算法的局限性引起的。

L波段差分干涉SAR卫星影像射频干扰分析与流程化抑制方法

陆地探测一号(简称“陆探一号”,LT-1)是中国首个以陆地SAR干涉测量为核心任务的L波段差分干涉合成孔径雷达卫星,通过双星绕飞、跟飞两种工作模式,利用差分干涉形变测量和干涉测高的技术,能够全天时、全天候实现高精度地表形变监测、地形测绘等任务。LT-1卫星运行于无线电业务分配比较密集的L波段,在部分地区面临着严重的同频射频干扰影响。射频干扰会导致干涉影像质量退化、相位失真以及相干性下降,进而直接影响形变场产品反演精度,造成对地遥感观测科学数据的浪费。为了降低射频干扰的不利影响,本文系统地分析了LT-1卫星影像中的射频干扰特性,提出了针对LT-1单视复数影像的业务化、批量化射频干扰检测和抑制方法。通过大批量实测卫星影像数据验证,本文方法能够高效地抑制影像中的射频干扰,恢复提升干涉影像对的相干系数。本文方法已经成功应用于自然资源部陆探一号地面处理系统中,为卫星影像业务化形变场产品生产提供支撑保障。

Seasonal Effects of Backscattering Intensity of ALOS-2 PALSAR-2 (L-Band) on Retrieval Forest Biomass in the Tropics

This research has used the L-band radar from ALOS-2 PALSAR-2 and field work data for evaluation of seasonal effects of backscattering intensity on retrieval forest biomass in the tropics. The effects of seasonality and HH, and HV polarizations of the SAR data on the biomass were analyzed. The dry season HV polarization could explain 61% of the biomass in this study region. The dry season HV backscattering intensity was highly sensitive to the biomass compared to the rainy season backscattering intensity. The SAR data acquired in the rainy season with humid and wet canopies were not very sensitive to the in situ biomass. Strong dependence of the biomass estimates with season of SAR data acquisition confirmed that the choice of right season SAR data is very important for improving the satellite based estimates of the biomass. This research expects that the results obtained in this research will contribute to monitoring of the quantity and quality of forest biomass in Vietnam and other tropical countries.

微波光子SAR最优子带融合的全分辨伪彩图生成方法

微波光子(MWP)雷达是一种通过光子器件对传统微波雷达硬件架构进行改进的新型雷达系统。借助光子器件卓越的物理特性,MWP雷达能够发射超宽带、高线性度的高质量线性调频信号,从而实现对目标的超高分辨率探测与成像。在目标成像与探测过程中,不同结构和特性的目标区域对不同频率信号的响应存在差异。因此,微波光子雷达具备通过散射差异生成伪彩图像的潜力,从而进一步提升微波光子合成孔径雷达(MWP-SAR)的信息获取能力。传统的遥感技术生成的伪彩图像分辨率较低,无法达到厘米级的分辨。因此,该文提出了一种在保证MWP-SAR高分辨率的前提下合成伪彩图像的方法。该算法首先建立了最优子带回波搜索模型,随后采用最优子带搜索算法对超宽带回波进行处理,以获取散射特性相差最大的子带回波通道。再对多子带差异图像进行色彩合成,通过这一处理步骤,能够生成对目标散射特性最佳描述的伪彩图像。同时,为了确保MWP-SAR的分辨率不受到损失,建立了一个融合模型,将全分辨率的SAR图像与多子带图像相融合,以维持伪彩图像的高分辨率。最终,通过实测的机载MWP-SAR数据成功地合成了全分辨率的伪彩色图像,从而验证了该算法的有效性。该算法可以使得MWP-SAR在成像时获取更多的目标信息,为成像雷达微波视觉的实现提供辅助。

Ka频段35.5-36 GHz低轨SAR卫星对地面雷达的干扰特性分析

针对使用Ka频段的合成孔径雷达(Synthetic Aperture Radar,SAR)的近地轨道(LEO)卫星对我国地面雷达系统的潜在干扰问题开展研究,在梳理国际电信联盟技术建议书和《无线电规则》的基础上,通过理论分析和干扰仿真等手段,对特定搭载SAR载荷的低轨卫星在完整周期内对地面气象雷达的干扰问题进行分析计算。研究结果表明,在SAR卫星与地面气象雷达有重叠部分的频段,考虑雷达部署特性和卫星轨道特性,卫星对地面气象雷达不会产生严重干扰。分析过程和结果对类似场景的星地频率兼容分析提供参考,对Ka频段雷达和SAR的工程预研和应用具有指导意义。

基于邻域统计分布变化分析的UWB SAR隐蔽目标变化检测

该文针对载机不同航迹条件下所得多时相UWB SAR图像灰度值存在较大起伏,严重影响了基于像素灰度值差异的变化检测算法性能,提出了一种基于邻域统计分布变化分析的UWB SAR隐蔽目标变化检测方法。该方法将Gram-Charlier展开理论同秩序滤波器相结合对多时相图像中每个像素邻域的统计分布进行估计,进而借助K-L散度理论对多时相图像邻域统计分布变化进行定量分析以检测目标对应的变化区域。实验结果表明,该文方法能够更好地适应不同航迹UWB SAR图像间灰度起伏的影响,取得更好的检测结果。

超宽带SAR探雷试验系统

超宽带SAR能够穿透地表远距离探测雷场或单个地雷。该文详细介绍了国防科技大学的超宽带SAR探雷系统:Rail-GPSAR系统及其信息处理技术。通过大量的外场试验证明,Rail-GPSAR系统能够有效检测到土壤中埋设的地雷。

非线性Chirp Scaling在机载SAR成像中的应用

非线性Chirp Scaling算法可以处理大耦合SAR回波,实现精确聚焦。与CS算法类似,NCS操作引起了距离向频谱扩展、调频率微调及距离压缩曲线偏移,只有在一定的成像测绘带宽度内这些影响才能被忽略。针对这一问题展开论述,通过仿真比较了NCS算法应用于典型机载L波段和P波段SAR成像时对距离谱的影响,从而确定可以理想聚焦的测绘带宽度。该结论对分段成像有一定的指导意义,应用于某机载P波段UWBSAR实测回波成像。

二阶运动补偿对低频超宽带SAR视线误差补偿的影响

视线误差补偿是低频超宽带合成孔径雷达(UWB SAR)成像处理的关键,该文主要研究基于测量数据的距离空变视线误差补偿,即二阶补偿。标准的二阶补偿在推导的过程中,对回波进行了一定的近似,认为距离空变视线误差对回波距离迁徙校正(RCMC)没有影响,而这个近似条件,在低频超宽带SAR中是不满足的。针对这个问题,该文对二阶补偿在低频超宽带SAR中的应用进行了分析,研究了3种二阶补偿方法,即:二阶补偿位于RCMC之后完成;二阶补偿位于RCMC之前完成;沿距离向划分子带进行二阶补偿。文中对3种二阶补偿方法进行了对比分析,并对每种补偿方法中存在的误差进行了分析。最后采用仿真以及实测低频超宽带SAR数据验证了文中分析的正确性。

超宽带SAR子孔径NCS实时成像算法

本文提出了一种适用于超宽带SAR实时成像的子孔径非线性CS(Nonlinear Chirp Scaling)算法,该算法利用方位向信号分量的时间和频率的锁定关系,在时域中互不重叠地划分子孔径,大大降低了系统存储量和运算量的需求,并采用时域加权方法将非重叠子孔径划分造成的假目标抑制到-31dB;此外,将MD自聚焦技术融入子孔径结构中,实现对大孔径复杂运动误差的有效补偿。仿真数据和实际数据验证了该算法的有效性。

脉冲卷积干扰技术在超宽带SAR中的应用分析

为探讨脉冲卷积干扰技术在超宽带SAR中应用的可行性,详细分析了距离像和二维像的干扰效果,发现在二维图像中,方位向的聚焦性能明显下降。通过对目标回波和干扰信号处理流程的分析,发现超宽带SAR空变特性是导致二维图像散焦的根本原因。提出对干扰信号进行相位调制,调整干扰信号的分布曲线,以降低空变特性的影响,取得了较好的干扰效果。研究表明,距离向的干扰效果与常规雷达一致,可以形成滞后的假目标欺骗干扰,改进的脉冲卷积干扰大大提高了方位向聚焦性能,用于对超宽带SAR进行假目标干扰。仿真结果验证了理论分析的正确性。

基于SAR的海上溢油监测最佳探测参数分析

基于SAR数据,在后向散射系数计算的基础上,从波段、极化方式、入射角等方面开展了海上溢油监测参数分析,结果表明：基于SAR的海上溢油监测,从波段分析,X波段与C波段较L波段更适合监测海上溢油;从极化方式分析,VV极化较HH,HV极化更适合监测海上溢油;从入射角分析,在计算溢油与海水临界值时,经多次实验,位于远入射角的疑似溢油不易与海水分离,而相对近入射角的疑似溢油较容易与海水分离。ALOS PALSAR影像的入射角约为23°~43°,COS-MO-SlyMed入射角为32°~35°,易于将海水与溢油分离的入射角大致为23°~35°。

基于机载P-波段全极化SAR数据的复杂地形森林地上生物量估测方法

【目的】利用国产合成孔径雷达(SAR)系统(CASMSAR)获取的机载P-波段全极化SAR(PolSAR)数据,分析SAR对森林地上生物量(AGB)的响应与地形的关系,建立融合地形因子的高精度多项式模型,以提高森林AGB的估测精度。【方法】首先以基于机载激光雷达(Li DAR)数据得到的研究区坡度分布图与结合实测样地AGB数据得到的森林AGB分布图作为参考数据进行系统抽样,分析森林AGB与P-波段PolSAR后向散射强度的关系以及不同坡度下二者的相关性变化;然后利用Li DAR得到的高精度数字高程模型(DEM)结合机载P-波段的轨道数据计算当地入射角,进而建立以后向散射强度、当地入射角以及雷达视角为输入特征的多项式统计模型,同时将以上系统抽样得到的样本一部分作为模型训练样本,一部分作为精度检验样本。为避免样本尺度引起的偶然性,检验了20 m×20 m至100 m×100 m不同样地尺度下的估测精度。【结果】以90 m×90 m样本为例,当坡度为0°~5°时,引入当地入射角(第2组特征)的估测精度与未引入当地入射角(第1组特征)的估测精度分别为:决定系数(R^2)为0.634和0.634,均方根误差(RMSE)为12.07和12.08 t·hm^(-2),总精度(Acc.)为78.91%和78.89%;当坡度为5°~10°时,第2组特征与第1组特征的估测精度分别为:R2为0.524和0.523,RMSE为13.52和13.97 t·hm^(-2),Acc.为80.57%和80.52%;当坡度大于10°时,第2组特征与第1组特征的估测精度分别为:R^2为0.628和0.519,RMSE为13.16和15.70 t·hm^(-2),Acc.为81.05%和78.55%。随着样地尺度增大,2组特征的估测精度均增大,且第2组特征的估测精度大于第1组。【结论】当坡度小于10°时,地形对森林的后向散射强度几乎无影响;当坡度大于10°时,地形的影响显著,在不同尺度下,引入当地入射角的估测模型均可以有效提高估测精度,充分说明模型的有效性和稳定性。此外,随着尺度增大,无论采用的模型是否考虑了地形影响,其估测精度都逐渐提高并趋于稳定,揭示出对复杂地形下森林AGB估测模型效果的评价必须考虑尺度的影响,且参考样地要足够大,否则难以得到客观的结论。