短时高斯包络线性调频基自适应信号分解算法

作为一种参数化时频分析的方法,基于高斯包络线性调频基自适应信号分解的快速算法具有分辨力高、零交叉项和计算量小的优点,在信号时频分析中具有独特的优势和广阔的应用前景.然而该快速算法却存在由于采样点初值选择不当而造成分解失效的缺点,虽然后来的基于优化初值选择的自适应高斯包络线性调频基信号分解对初值选择算法进行了改进,提高了分解性能的稳定性,但仍存在较多的问题没有解决.本文将对这些问题进行研究和改进,并提出短时自适应高斯包络线性调频基信号分解算法.算法通过加短时窗来增强时频中心定位的准确性,通过控制采样基时宽来获取有效的初始方差取值范围,从而提高了分解的自适应性和稳定性.对仿真信号和语音信号的分解结果表明了该算法的有效性.     

LMD算法与运动想象脑电信号的时频分析

脑电信号是极其复杂的非平稳信号,为了精确处理运动想象脑电信号,采用LMD(局域均值分解)方法对其进行时频分析。首先给出仿真信号的LMD分解及时频分布,而后对左右手运动想象脑电信号进行LMD时频分析。研究结果表明,LMD具有较强的时频刻画能力,能够精确描述脑电信号的非线性时变特性,是对脑电信号进行时频分析的有效方法。     

气缸压力的时频分析及其在内燃机故障诊断中的应用

对气缸压力进行时-频分析,探讨了气缸压力信号与气阀机构状态之间的关系.对气缸压力信号进行二进小波分解,计算分解后尺度1上信号各频带的能量比,从中提取诊断特征量,从而对气阀机构进行故障诊断.结果表明此方法是可行、有效的.     

基于Wigner分布时频遮隔的信号分解算法

综合特征值分解及Wigner分布时频遮隔提出了一种信号分解算法,并推广应用于其他交叉项抑制时频表示.对于由时频面上互不重叠分量合成的多分量信号,证明了信号分量可与各分量Wigner分布之和的逆Fourier变换的特征值分解相对应;通过阈值法可从抑制交叉项时频表示获得信号时频支撑区域,以此为模板遮隔Wigner分布可减少交叉项并保持自项聚集性,其逆Fourier变换的特征值分解就可实现多分量信号分解.仿真实例分析结果表明了该理论与算法的正确性和实用性.最后分析了算法性能并拓展了其实用范围.     

一种新的跳频信号参数盲估计算法

本文针对通信对抗中的跳频信号参数盲估计问题,提出了一种基于原子分解算法的跳频信号参数盲估计方法.根据跳频信号内部结构的特点,以加窗正弦函数为基函数构造了一种与跳频信号匹配的3-参数时频原子字典,将跳频信号分解为有限个3-参数时频原子的组合,最终根据这些时频原子的参数值来估计跳频信号的参数.仿真实验表明,该方法能够在未知任何先验知识的情况下,对跳频信号的跳周期、跳变时刻和跳频频率进行有效估计.     

参数化时频分析综述

参数化时频分析是处理非平稳信号的重要手段。该文综述了参数化时频分析的产生、原理、快速算法。分析了现存的参数化时频分析方法存在的问题,提出了进一步提高分解自适应性和实时性的思路,指出了将图像处理方法和摄动理论应用到参数化时频分析方法中等有价值的研究方向。     

基于自适应短时Chirplet分解的高性能时频分布重构

通过傅里叶变换得到的频谱能够反映信号所包含的频率成分，但无法揭示瞬时频率随时间的变化特性。为满足工程应用中大量非平稳信号的分析需求，能够同时描述信号时域和频域特征的时频分析方法得到了广泛关注和深入研究。然而，传统时频分析方法所得到的时频分布往往具有较低的能量聚集性和较强的交叉项干扰，难以支撑信号时频特征的准确表达和提取。通过对信号内在稀疏特性进行挖掘和利用，能够有效提升信号时频分布的质量。本文通过对信号的相位函数进行泰勒展开，阐述了信号稀疏时频分解的实质，并分析了现有稀疏类时频分析的方法不足。在此基础上，提出了一种基于自适应短时Chirplet分解的高性能时频分布重构方法。首先，利用与信号时频特性自适应的窗函数为每一时刻生成了具有最强拟平稳性的最优短时信号；其次，提出了一种Chirplet字典的简化设计方法，利用得到的Chirplet字典对上述短时信号进行稀疏分解，基于分解结果实现了短时信号中心时刻瞬时频谱的参数化重构；最后，按时间顺序排列所有时刻的瞬时频谱，得到了信号能量聚集性高且不含任何交叉项干扰的高性能时频分布。仿真实验表明，所提方法有效改善了传统稀疏类时频分析方法结果中时频曲线...     

自适应旋转投影分解法

本文提出种新的时－频分解方法－自适应旋转投影分解法。在表征信号空间的线性调频高斯信号集上，我们针对原始信号自适应地搜索出一组与信号匹配最好的基函数序，以此 用尽可能少的基函数来重构信号子空间。     

跳频信号时频分析的一种新方法

利用魏格纳-威尔变换等非线性时频分析方法,对跳频信号进行时频分析存在交叉项干扰的问题.为提高对跳频信号进行时频分析的准确度,提出一种新的时频分析方法.对跳频信号首先进行奇异点的检测,根据奇异点的位置将跳频信号划分为不同的单载频信号,然后利用非线性时频分析方法对单载频信号进行逐个处理,最后将得到的多个单载频信号的时频关系按跳频规律进行组合,进而得到完整的跳频信号时频关系.仿真验证了新方法可有效抑制交叉项,准确可行.     

利用遗传算法实现基于MP的跳频信号稀疏分解

在目前的通信领域中,跳频信号的应用越来越广泛,而信号的稀疏表示在信号处理的许多方面都有着重要的应用.将跳频信号稀疏分解后得到的稀疏表示可以方便的应用到跳频信号的参数估计及后续处理中去.本文针对目前基于MP (Matching pursuit)的跳频信号稀疏分解中运算量巨大的问题,采用遗传算法(GA)快速地寻找MP算法中每一步分解的最佳原子,提高了信号稀疏分解的速度.仿真分析验证了此方法的有效性和适用性.     

二维Hilbert-Huang变换的分解方法研究

该文根据Hilbert-Huang变换的原理,给出了二维内蕴模式函数分量的递推形式,实现了二维Hilbert—Huang变换的分解方法,并在图像分解应用中取得了满意的效果,从而拓展了Hilbert—Huang变换的应用范围。通过把原始图像自适应分解成有限数量的子图像,图像的细节能清晰地被分解出来,这在数字图像处理中有很重要的意义。     

Application of the high-gain substrate-superstrate configuration to dielectric leaky-wave antennas

The high-gain substrate-superstrate configuration, which was proposed to increase the gain in printed circuit antennas, is applied to dielectric leaky-wave antennas (LWAs) to improve its frequency response. Analysis of a slitted suspended dielectric rectangular waveguide is carried out using a full-wave method. It is proved that the minimum values of the leakage constant of the leaky-wave mode for the suspended configuration are related to the high-gain resonance conditions. Moreover, it is found that the suspended LWA exhibits very small beamwidth variations in a large frequency bandwidth. It is well-known that inhomogeneous filled LWAs suffer from variation of beamwidth as the angle of maximum radiation is scanned with frequency. The proposed topology can be adjusted so that a flat response of the beamwidth can be obtained in a large frequency band, while maintaining the frequency-scanning behavior of the LWA.     

Hilbert-Huang变换的自适应频率多分辨分析研究

Hilbert-Huang变换方法能自适应地提取非平稳数据的局部均值曲线,将复杂的叠加信号分解成有限数量的、且有物理意义的内蕴模式分量函数,从而得到有意义的瞬时频率和希尔伯特时频谱.它是一种局域波分析方法.其特点是比小波分析有更高的时频分辨率,没有Wigner-Ville分布的交叉项,特别适合分析非平稳数据.本文根据Hilbert-Huang变换的原理,推导出内蕴模式函数的递推表达式,给出了希尔伯特谱的最高频率分辨率,首次提出了一种新的的自适应频率多分辨分析原理和方法,从而完善了局域波分析的理论.     

Studies of suppression of the reflected wave and beam-scanning features of the antenna arrays

This paper describes a two-directional linear scanned design by integrating a short leaky-wave antenna (LWA) with aperture-coupled patch antenna arrays. This architecture proposes a technique not only having the advantage of suppressing the back-lobe due to the reflected wave in the short LWA but also producing two separate linearly scanned beams, each of them radiating in a different region of space (in both the front side and backside of the LWA). In this design, most of the reflected wave of the short LWA is coupled to the patch antenna arrays on the backside of the substrate. The phase of this coupled signal to each antenna element is adjusted by tuning the individual phase shifter in order to control electronically the patch antenna main beam in the cross plane (x<0). Meanwhile, on the front side, the main beam of the short LWA can be simultaneously scanned in the elevation plane (x>0) by changing the operating frequency. Hence, the two linear beam-scanning radiation patterns of individual direction can be created independently, including a narrow beam in the elevation plane (xy plane at x>0) at the front side and a broadside beam in the cross plane (xz plane at x<0) on the backside. The measured results show that the reflected wave of the short LWA in the proposed design is suppressed 8 dB as compared with a traditional short LWA without the aperture-coupled antenna arrays at 10.5 GHz. As a result, this novel architecture provides more flexibility both in the upward elevation plane (H plane) and the downward cross plane (backside-E plane) for possible beam-scanning applications in microwave communications and remote identification.     

2-D periodic leaky-wave Antennas-part II: slot design

The far-field radiation patterns of a two-dimensional (2-D) periodic slot leaky-wave antenna (LWA) are studied. The antenna consists of a two-dimensional periodic array of slots in a conducting plane that is printed on top of a grounded dielectric slab. The antenna is excited by a simple source such as a dipole inside the slab. Reciprocity along with the spectral-domain method is used to calculate the far-field pattern, and the radiation characteristics of the structure are investigated. A comparison between the present periodic slot LWA and a 2-D periodic patch LWA discussed in Part I is given to show the advantages of the slot antenna for certain applications. The slot LWA can achieve high directivity patterns, and a circularly-polarized version of the antenna can achieve good circular-polarization at broadside.     

Effect of reactive loading in microstrip leaky wave antennas

The influence of capacitors periodically soldered along the radiating edges of a leaky wave antenna (LWA) is described. As the propagation characteristics are modified, the main beam is tilted from the angle observed for the unloaded LWA. This property allows beam steering applications at a fixed frequency if bias-controlled reactances are used     

2-D periodic leaky-wave antennas-part I: metal patch design

The far-field radiation characteristics of a two-dimensional (2-D) periodic leaky-wave antenna (LWA) constructed from a periodic array of metal patches on a grounded dielectric substrate is investigated. A simple dipole source is used as the excitation. Reciprocity together with a periodic spectral-domain method of moments is used to calculate the far-field pattern. Design rules for the scan angle, the substrate dielectric constant, and the periodicity are provided. Finally, a comparison of the 2-D periodic LWA and a dielectric-layer LWA is given to show the similar performance of the two antennas.     

A CPS Leaky-Wave Antenna With Reduced Beam Squinting Using NRI-TL Metamaterials

A reduced beam-squinting printed leaky-wave antenna (LWA) is proposed, comprising cascaded negative-refractive-index transmission-line (NRI-TL) metamaterial unit cells. Each NRI-TL unit cell is implemented in co-planar strip (CPS) technology and consists of a host TL loaded with series interdigitated capacitors and shunt meandered inductors. Periodic analysis is applied to the NRI-TL unit cell in order to extract the dispersion and Bloch impedance characteristics. Subsequently, the angular variation of the main radiated beam with frequency or ldquobeam squintingrdquo is derived, based on the expression for the Bloch propagation constant of the NRI-TL line. It is shown that by operating the LWA in the upper right-handed band where the phase and group velocities are closest to the speed of light, the beam squinting that the antenna experiences can be minimized. The theoretical performance of the LWA is verified through full-wave simulations and measurements of a fabricated prototype designed to produce a radiated beam at an angle of at GHz. This 20-element NRI-TL LWA exhibits a measured return-loss bandwidth below dB of 0.91 GHz (18.2%), and an average beam squint of 0.031/MHz. The proposed NRI-TL LWA is uniplanar, differential and broadband, and therefore suitable for integration with other microwave components and devices.     

Effect of unit-cell size on performance of composite right/left-handed transmission line based leaky-wave antenna

The leakage rate and the scanning ability of composite right/left-handed transmission line based leaky-wave antennas (LWA) is investigated. It is demonstrated how the leakage rate is altered with unit-cells of different sizes. It is observed that the LWA with smaller unit-cells exhibits lower rate of leakage and higher gain at a cost of reduced bandwidth.     

Two-dimensional scanning leaky-wave antenna by utilizing the phased array

An aperture-fed patch antenna array is connected to the open end of a short leaky-wave antenna (LWA) to demonstrate the two-dimensional beam-scanning capability in this paper. This design not only offers another radiation path of the reflected wave, but also creates another scanning radiation pattern on the back plane of the substrate. The reflected wave of the LWA is equally separated by a power divider, modulated by each varactor-tuned phase shifter, and injected into two radiating aperture-coupled antennas. The operated frequencies are tuned to control the LWA main position in the elevation plane; meanwhile, by tuning the phase difference between two phase shifters, the main beam of the aperture-coupled antenna array can be scanned in the backside E plane. Experimental result shows that the suppression of the reflected wave can be 7 dB at 10.0 GHz with a short LWA length of 6 cm (two wavelengths). The H-plane and backside E-plane scanning radiation patterns have great potential in many applications and provide more flexibility to traditional designs.