Design of windows with steerable sidelobe dips

Based on the frequency sampling method, a novel and simple window design technique was established upon three theorems. The technique produces a set of windows which have simple expressions and the steerable sidelobe-dip (SSLD) property. By steering the dips in the sidelobes, it is easy to reduce the edge of the mainlobe, or to minimize the height of sidelobes, or to create a `hole' in the sidelobes if its desired to reduce spectral leakage at a particular frequency. It is found that windows constructed as a weighted sum of cosines over a finite support and with a -6 dB/OCT sidelobe falloff rate can all be simulated by appropriate SSLD distributions. In this sense, many good windows such as Hamming, Blackman, Blackman-Harris, and minimum sidelobe behaviors can be created with a minor constraint. This renders design flexibility for various applications. Finally, the new technique can be easily incorporated with other techniques to produce windows with hybrid merits     

Tapered beamforming for concentric ring arrays

In this paper, some conventional filtering windows are modified and applied to uniform concentric circular antenna arrays (UCCA) for spatial smoothing and sidelobe reduction. The modified windows are applied to individual rings of the array that will taper the corresponding current amplitudes. The resulted sidelobe level, beamwidth and stability for amplitude errors are discussed for the different proposed tapering windows where it shows a sidelobe reduction to about 49 dB as in the case of Binomial UCCA while the Hamming window shows the most immunity to tapered amplitude errors.     

Simplified Sidelobe Reduction Techniques for Concentric Ring Arrays

In this paper, a simplified sidelobe reduction technique for uniform concentric circular antenna arrays (UCCA) is proposed. This technique is based on modifying some conventional windows to control the amplitude feeding instead of using adaptive techniques which require excessive processing and calculations and suffer from the lack of practical application especially for UCCA. The modified windows are applied to individual rings of the array that will taper the corresponding current amplitudes. The resulted sidelobe level, beamwidth and stability for amplitude errors are discussed for the different proposed windows where it shows a sidelobe reduction to about 49 dB as in the case of Binomial UCCA while the Hamming window shows the most immunity to tapered amplitude errors.     

Synthesis of windows from raised-cosine pulse

A set of windows, whose normalised main lobe widths fall between those of Hamming and the sum-cosine window, are developed. The windows are compared with Kaiser's near optimum zeroth-order Bessel windows. The results show that the new windows yield 4 to 9 dB improvement in the first sidelobe gain, and the improvement in maximum sidelobe gain varies from 2.8 to ?0.85 dB, compared with that of Kaiser windows. The energy in the main lobe of Kaiser windows is at most 0.005% larger than that of the new windows. The distinct advantage of the windows is their very simple form, similar to that of a Hamming window.     

A set of sum-cosine window functions

This paper presents a set of windows, called sum-cosine windows, whose first side-lobe level varies from ?39-30 to ? 67-66dB, while the peak sidelobe offers ?39-30 to ? 6312dB attenuation. The asymptotic decay rate of the sidelobe envelope ranges from 12dB per octave to 36dB per octave. However, the main-lobe width of these windows falls in between Hamming and Blackman windows and Black-man windows and the optimum windows, proposed by Harris and Nuttall. The distinct advantage of these windows is their simple form, resulting in easy implementation, compared to the near-optimum windows proposed by Kaiser.     

基于内点法的动目标检测滤波器组设计

雷达系统常采用基于快速傅里叶变换的方法实现动目标检测(MTD)滤波器组,其关键是通过加窗降低滤波器副瓣,但普遍存在加窗的结果使滤波器零点产生偏移,不能保证非零速滤波器在零频形成真正零点。文中基于窗函数的理想频率响应构造了简化的目标函数,以零频形成零点为约束实现滤波器峰值旁瓣电平比最大化,采用内点法求解该问题,并推导了窗函数系数的显式表达式。同时,引入了扰动因子,以保证迭代过程的收敛性。仿真表明MTD滤波器组满足地杂波抑制的需求,且峰值旁瓣电平为-41 dB。该方法为MTD应用提供了一种新思路。     

Optimum approximations to Dolph-Chebyshev data windows

The narrow main lobe widths of Dolph-Chebyshev (1946) spectral windows can be approximated to within about 4%, with sidelobe depression to at least -98 dB, by windows defined with four Fourier series coefficients. Two windows may be particularly attractive, the opt59 and opt71 windows, since the true value of the fourth coefficient is zero     

Sidelobe reduction of asymmetric linear array by spacingperturbation

The sidelobe reduction of asymmetric linear arrays by tuning element spacings is presented. Using appropriate point matching and least square error approximation of the radiation power distribution, further sidelobe reduction may be achieved with slight beamwidth broadening. Two simulation results are given to show the feasibility of the proposed technique     

基于改进SVA和压缩感知的SAL旁瓣抑制算法

针对机载合成孔径激光雷达实测数据成像中旁瓣较高的问题,提出一种新旁瓣抑制算法。压缩感知理论表明,稀疏信号恢复重构过程的同时,信号旁瓣会被压低,但合成孔径激光雷达图像不是稀疏的。针对这一问题,提出了一种基于改进SVA（Spatially Variant Apodization）和压缩感知重构SAL图像的旁瓣抑制算法。首先,利用改进SVA算法将SAL图像变稀疏,然后再利用压缩感知算法对稀疏图像进行恢复。分别对SAL仿真数据和实际高旁瓣SAL复图像进行抑制旁瓣处理。仿真结果表明:该算法能够在保证主瓣不被展宽的前提下有效抑制SAL旁瓣。     

Butterworth Window for Power Spectral Density Estimation

The power spectral density of a signal can be estimated most accurately by using a window with a narrow bandwidth and large sidelobe attenuation. Conventional windows generally control these characteristics by only one parameter, so there is a trade-off problem: if the bandwidth is reduced, the sidelobe attenuation is also reduced. To overcome this problem, we propose using a Butterworth window with two control parameters for power spectral density estimation and analyze its characteristics. Simulation results demonstrate that the sidelobe attenuation and the 3 dB bandwidth can be controlled independently. Thus, the trade-off problem between resolution and spectral leakage in the estimated power spectral density can be overcome.     

一种零陷展宽稳健旁瓣相消算法

受到实际条件的限制,自适应旁瓣相消器通常不可能频繁地更新自适应权值,使得其在对抗空域非平稳干扰时,会出现权值失配现象,严重影响干扰抑制性能。该文从空域密集干扰产生宽零陷的角度出发,提出一种适用于自适应旁瓣相消器的零陷展宽算法。该算法通过对主通道的合成权值和辅助天线间的协方差矩阵同时进行锥削实现零陷展宽,锥削向量和锥削矩阵只与阵元位置和展宽宽度有关,可以离线计算,在线直接调用,实现简单,适合工程实际使用。仿真实验证明,该文方法可以有效展宽自适应零陷,增强自适应旁瓣相消器对抗空域非平稳干扰时的稳健性。     

一种改进窗函数非线性组合法的旁瓣抑制性能研究

为解决在雷达脉冲压缩过程中通过海明窗、汉宁窗等加权方式降低旁瓣而引起主瓣展宽、分辨率下降的问题,提出了一种以常用窗函数为基窗函数的改进窗函数非线性组合法。首先,相较于基窗函数,基于窗函数加权脉冲压缩的原理,证明窗函数线性组合法在主瓣展宽不变时可获得更好的旁瓣抑制能力;并在此基础上进一步证明改进的窗函数非线性组合法具有更优的旁瓣抑制能力。然后,通过对改进的窗函数非线性组合法在三角窗、汉宁窗、海明窗、布莱克曼窗等作为基窗函数时的脉冲压缩性能仿真与分析,验证了该方法使用不同基窗函数均可在主瓣展宽不变、信噪比损失增加低于0.5 dB的前提下,将峰值旁瓣相比凯塞窗降低4 dB以上、相比几种常用窗函数降低7 dB以上。最后,通过多目标的仿真实验验证,相比于不同的基窗函数,改进窗函数非线性组合法具有更优的弱小目标检测能力。     

A Family of Optimal Window Functions for Spectral Analysis with the Spectrum Sidelobe Falloff Rate Multiple of 12 dB per Octave

Journal of Communications Technology and Electronics - A synthesis problem is solved for low-order windows with the sidelobe spectrum falloff rate equal to 12n decibel per octave (dB/oct), where n...     

Figures of merit of windows for power density spectrum estimation with the DFT

The figures of merit of windows for harmonic analysis proposed by Harris [1] are discussed, and other figures of merit are investigated. An interesting result is that for the estimation of the power density spectrum from a limited amount of data, the only relevant characteristic of a window is the spectral sidelobe level.     

A new optimal window [signal processing]

An optimal window that can provide the best tradeoff between the peak sidelobe level and the total sidelobe level is presented. Necessary and sufficient conditions are established for the optimal window. A design algorithm is presented, and examples are discussed. The examples demonstrate that the window is capable of much better performance than previously available windows, such as the Hamming window. Relationships between the maximum error and the mean-squared error are explored for the window optimization problem. It is concluded that the minimax and least squares approximations are both fundamentally inefficient. This conclusion is supported by experimental evidence and mathematical analyses     

变量切趾技术在SAR/ISAR图像处理中的应用

SAR/ISAR图像处理需要进行二维傅里叶变换,傅里叶变换本身具有较高的旁瓣电平,虽然通过加权处理可以降低旁瓣电平,但是主瓣的分辨率会降低.变量切趾技术在SAR图像处理中能够抑制旁瓣电平,同时保持图像的高分辨率。该文分析了传统的变量切趾技术和算法,通过加强约束条件,提出了改进的变量切趾算法.与原有方法相比,获得更高的分辨率和低的旁瓣电平,对一幅二维ISAR图像进行处理证明了这种方法的正确性.     

New hyperbolic function window family

A new window family is introduced, whose normalised half mainlobe width falls between those of rectangular and Hamming windows. The proposed window has two variable parameters by which the mainlobe width and the sidelobe levels can be controlled and used for many digital signal processing applications. This window is compared with a Kaiser-Bessel window, and a tanh window     

单脉冲脉内互补低距离旁瓣雷达波形设计

雷达脉冲压缩的距离旁瓣较高将会导致遮蔽效应的产生,已有的低旁瓣波形设计都是基于全脉冲相关进行处理。本文利用波形组合的方法进行波形设计,基于单脉冲脉内分段脉压信号处理方式和互补码自相关求和零旁瓣特征相结合,利用频域正交设计,将两个或多个互补序列调制至不同频点以子脉冲的形式分段合并为恒模单脉冲雷达波形。仿真试验表明,本文设计的单脉冲脉内互补低旁瓣波形脉压后的峰值旁瓣电平和积分旁瓣电平较低,分段脉压结合互补码零旁瓣特征的信号处理方式虽然会导致0.89 dB左右的信号处理增益损失和主瓣展宽,但却能够突破部分相位编码信号的峰值旁瓣电平下限。强弱目标场景仿真表明,与线性调频信号相比,本文提出的雷达波形不会导致强目标的副瓣对弱目标的遮掩。恒虚警检测仿真表明,在剔除强目标峰值后,本文所提波形对弱目标的检测概率要优于传统的线性调频信号。     

Sidelobe Suppression in Low and High Time-Bandwidth Products of Linear FM Pulse Compression Filters

The peak sidelobe suppression of unweighed linear FM surface acoustic wave filters limits the dynamic range of pulse compression systems. Using a discrete inverse Fourier transform "sampling technique" and complex Fresnel integral algorithms, this paper extends previous results of other authors from a time-bandwidth product of 50 up to the high value of 720. In the present work, the weighting is applied in the frequency domain, employing an external Hamming weighting function. The output waveforms are determined for different sampling rates. The results show that a peak sidelobe suppression of -38 dB from the main Iobe is achieved for high time-bandwidth product (TB = 720) at a sampling rate of 512 with broadening in the main lobe, while it is -41 dB for a low time-bandwidth product of TB = 50. Also, the paper contains charts showing the sidelobe suppression of unweighed and Hamming externally weighted linear FM pulse compression filters at different values of time-bandwidth products TB (50,100,250,370,510,720) with different central frequencies, dispersion times, and bandwidths B. The skirt steepness, sidelobe ripple rejection, Gibbs ripples of the wave spectrum, reduction of the insertion loss, and suppression of Fresnel ripples are also compared.     

层析SAR系统基线优化设计

自然场景3维影像重构是层析合成孔径雷达(TomoSAR)的重要应用。传统方法在沿高程维进行层析处理时,均通过对等距线阵模型进行加权的方式,以主瓣展宽为代价来抑制方向图旁瓣水平。针对该问题,该文建立一种基于非等距线阵的峰值旁瓣比极小极大优化模型,即在约束主瓣宽度一定的情况下,通过阵元位置的优化配置来获取观测场景视角范围内任意指向的最优旁瓣水平;提出一种目标函数离散栅格化方法,进而采用序列二次规划(SQP)方法并结合差分进化算法特有的全局记忆能力,以获取最优阵元配置方案。对PolSARpro全极化层析SAR仿真数据的处理结果表明该方法能够有效地应用于自然场景的3维影像重构。