地下目标散射的FDTD计算

该文给出了一种利用时域有限差分法(FDTD),结合各向异性完全匹配层(UPML)以及互易原理,计算地下目标雷达散射截面的计算方法。通过数值实验,对这种计算方法的数值性能作了仔细研究。给出了一批新的不同电尺寸、不同形状、不同介电常数地下目标的雷达散射截面计算结果。     

无限长圆柱体的宽频带隐身罩的设计与仿真

外形隐身技术在国内外研究与应用领域拥有大量的实验验证与实践应用。本文主要讨论了基于电磁波绕射原理的无限长圆柱体隐身实现方法,并对隐身效果进行讨论。综合讨论了外形隐身对于特定结构实现降低雷达散射截面(RCS)的方法,文章进而分析结构的S 参数进行验证,并简要分析其可能的原理与实现方法。改变结构后仍然能够产生隐身效果,中心频点会降低。最后分析新型结构能够减小相应的电尺寸的原因。     

Microstructural study of dielectric breakdown in glass-ceramics insulators

Novel glass-ceramic materials based on Na and Ca-rich feldspar crystallizations with a hierarchical micro-nanostructure shown the largest dielectric strength, >57 kV/mm, reported at room temperature in ceramic insulators, due to a large amount of interfaces that favor scattering processes of charge carriers. Dielectric breakdown tests with temperature indicated they withstood up to 200 °C, with dielectric strengths of 30 kV/mm and 44 kV/mm for anorthite and albite-based glass-ceramics, respectively. These values are even larger than the ones obtained at room temperature for most of the current ceramic insulators. Microstructural characterization and micro-Raman spectroscopy carried out after breakdown allow determining the dielectric breakdown mechanisms. Glass phases in the surroundings of the crater because of local melting and fast cooling are identified. These results make feldspar based glass-ceramics suitable for electrical insulator applications at room and high temperature. Moreover, dielectric breakdown mechanism may allow tailoring new high insulating application in the future.     

利用多层快速多极子技术对随机粗糙表面SAR回波信号统计特性的研究

该文主要目的是研究随机粗糙面SAR回波信号的统计特性。结合传统的Monte Carlo方法,利用多层快速多极子算法严格高效地模拟了三维随机粗糙面的SAR回波信号。依据常用SAR系统,将发射波的仰角固定在45,并让方位角在88~92之间变化,得到若干组随机表面的回波。计算回波幅值和相位的均值,得到一些值得关注的结论。     

基于LUT的HPA数字基带预失真方法研究

该文深入研究了OFDM系统中基于查询表LUT方法的HPA数字预失真技术。针对传统LUT方法收敛速度非常慢的不足,有关文献提出了相应的改进措施。该文从误码率BER,功率谱密度PSD和算法收敛速度几个方面进行了算法性能的仿真比较分析,指出以上算法存在的不足,并提出了新的改进方法,仿真及分析结果表明了该文提出改进方法在性能上的优越性。     

A fractal metamaterial based printed dipoles on a nickel oxide polymer palm fiber substrate for Wi-Fi applications

In this paper, a novel antenna circuit based metamaterial (MTM) structures is proposed for Wi-Fi applications. The antenna consists of two dipoles with 3 × 5 Hilbert-shaped MTM array printed with Sliver Nanoparticles Conductive Ink (SNPCI). The antenna substrate is mainly created from INP composite of: Iraqi Palm Tree Remnants (IPTR) and Nickel Oxide Nanoparticles (NONP) with Polyethylene (PE) mixture. The relative permittivity (ε_r) and permeability (μ_r) are measured using an open-stub microstrip resonator to find ε_r = 3.106 − j0.0314 and μ_r = 1.548 − j0.0907 at the frequency band of interest. Numerically, Finite Integral Technique (FIT) and Finite Element Method (FEM) of CSTMWS and HFSS formulations, respectively, are invoked to investigate the antenna performance. Experimentally, the antenna exhibits two resonances, |S₁₁| < −10 dB, at 2.45 GHz and 5.8 GHz with gain of 2.6 dBi and 4.8 dBi, respectively. The antenna shows a bandwidth of 500 MHz around the first resonance and 2 GHz at the second resonance. The measured radiation patterns at the two resonances are found to be mainly directed toward the antenna end fire with radiation efficiency of 0.8 and 0.65 at the first and second modes, respectively. Finally, the proposed antenna performance is compared against a reference antenna to reveal the excellent enhancements.     

基于SDL的无线局域网MAC协议设计与实现

目前较流行的无线局域网MAC芯片的设计方案是在设计中嵌入ARM微处理器，其核心内容是WLAN MAC协议的设计实现。文章利用SDL语言实现该协议，并对协议进行了仿真验证。     

Accurate signal detection for BPSK-OFDM systems in time-varying channels

Binary phase shift keying (BPSK) orthogonal frequency division multiplexing (OFDM) has been adopted in the fourth-generation wireless communications. However, the real-valued property of BPSK-OFDM signals has not yet been utilized for channel equalization. In this work, this property is employed to develop a new equalizer based on the minimum mean square error (MMSE) criterion, leading to considerable enhancement in signal detection. In particular, the proposed equalizer is able to achieve 3 dB improvement over the existing MMSE equalizer in large signal-to-noise ratio region, and is more robust against channel estimation errors. Moreover, successive detection technique employed in the devised method is able to make use of diversity in time-varying channels, resulting in further performance enhancement. Additionally, the computational complexity of the proposed approach is analyzed. Simulation results are included to illustrate its performance superiority and computational attractiveness.     

Role of composition and grain size in controlling the structure sensitive magnetic properties of Sm~(3+) substituted nanocrystalline Co-Zn ferrites

The nanocrystalline samarium substituted Co-Zn ferrites with chemical formula Co_(0.7)Zn_(0.3)SmyFe_(2-y)O_4(where y=0,0.01,0.02,0.03,0.04) were synthesized by sol-gel autocombustion route.The analysis of Xray diffractograms(XRD) reveals the formation of cubic spinel structure.The planes indexed from XRD analyses were confirmed in the selected area electron diffraction(SAED) image of the sample.Nanocrystalline nature of the particles in the ferrite samples was confirmed by TEM.The morphology was analyzed by scanning electron microscopy(SEM).Magnetic measurements show an increase in the magnetization for x ≤0.03.The decrease in magnetization due to spin canting is observed for x=0.04.The coercivity depends on Sm~(3+)doping concentration,grain size and saturation magnetization.The complex permeability of the ferrites was analyzed as the function of frequency and Sm~(3+)composition(y).The real part of complex permeability varies linearly with the grain size.     

FM and AM mode locking of the homogeneous laser--Part II: Experimental results in a Nd:YAG laser with internal FM modulation

In Part I of this paper [1], a theoretical analysis of the mode-locked homogeneous laser was given. In this part we present experimental results for the Nd:YAG laser with internal phase modulation. LiNbO3was used as the modulator crystal, and a method to measure the single-pass phase retardation of the modulator accurately at 1.06 μ is described in detail. The pulsewidth and spectral width of the mode-locked laser were measured as a function of depth of modulation, and good agreement with theory was obtained. Etalon effects in the laser were observed, and the results agreed very well with the theory. Mode-locked spectral bandwidths of up to 16 GHz, implying mode-locked pulses as short as 40 ps, were obtained.