A compact bandpass filter with enhanced stopband characteristics by an asymmetric cross-shape defected ground structure

In this paper, we present an effective technique to enhance stopband bandwidth for a bandpass filter by using an asymmetric, cross-shape defected ground structure (CSDGS). A single CSDGS can provide a higher attenuation rate near passband and broader stopband bandwidth. Moreover, with the asymmetric CSDGS, two different resonant frequencies can be excited and controlled independently, resulting in synthesizing a passband. The synthesized bandpass filter can be modeled by parallel LC resonant circuits in connection with T-networks. The bandwidth and insertion loss of this bandpass filter at 4.2 GHz is 28.6% and -1.44 dB, respectively, and 20 dB rejection in the stopband is up to four times the central frequency. All the synthesized bandpass filters have been measured and are in good agreement with simulated results.     

Low radar cross-section and high performances of microstrip antenna using fractal uniplanar compact electromagnetic bandgap ground

By using surrounding periodic second-uniplanar compact electromagnetic bandgap (UC-EBG) ground plane, a microstrip patch antenna working at X-band with low radar cross-section (RCS) and high performance was designed. The main parameters such as return loss, impedance bandwidth, RCS, radiation patterns and gains are presented and discussed. Comparison of the patch antenna with the surrounding periodic second-UC-EBG ground suggests that the second-UC-EBG has much lower RCS than the standard patch antenna at a band range 2-18 GHz. In addition, gain, bandwidth and radiation patterns of the former are all improved when compared with those of the latter.     

基于CPLD的超声相控阵高精度相控发射系统的实现

超声相控阵发射波束形成中的关键环节是对各阵元的发射相位延时进行精确控制，以得到灵活可控、指向性良好、焦点尺寸细小的聚焦声柬，从而获得被检物体的清晰成像。本文研制了基于复杂可编逻辑程器件（CPLD）和可编程数字延迟线（AD9501）的超声相控阵系统中的高精度相控发射系统。该系统可同时控制16通道，它的延时分辨率可达1ns，最大延时值达到655μs。     

Blocked element compensation in phased array imaging

In clinical applications using large apertures, a significant number of phased array elements may be blocked due to discontinuous acoustic windows into the body. These blocked elements produce undesired beamforming artifacts, degrading spatial and contrast resolution. To minimize these artifacts, an algorithm using multiple receive beams and the total-least-squares method is proposed. Simulations and experimental results show that this algorithm can effectively reduce imperfections in the point spread function of the imager. Combined with first-and second-order scatterer statistics derived from multiple receive beams, the algorithm is modified for blocked element compensation on distributed scattering sources. Results also indicate that compensated images are comparable to full array images, and that even full array images can be improved by removing undesired sidelobe contributions. This method, therefore, can enhance detection of low contrast lesions using large phased-array apertures.     

相控阵超声绝对声时法测量底面开口裂纹

针对工件内表面开口裂纹单面单侧定量检测困难的问题,采用相控阵超声绝对声时法(Absolute Arrival Time Technique,AATT)从单面单侧对不同厚度试块中的底面人工开口裂纹自身高度测量进行了数值仿真和实验,并对焊缝中的自然裂纹进行了AATT测量。对比AATT测量结果与常规衍射时差法超声检测(Time of Flight Diffraction,TOFD)测量结果并分析,发现AATT从单面单侧对底面开口裂纹进行定量测量可以达到与常规TOFD同样的测量精度。AATT操作简便,可单面单侧定量测量2 mm以上底面开口裂纹的自身高度。     

相控线阵声源在套管井中的应用

在常规的单极子套管井测井中,由于过套管测量,即使在I、II界面均胶结好的状况下,测量的地层波信息也比较弱。利用相控线阵声源的声束偏转和能量聚焦技术,可大大提高声源的辐射强度和信噪比。采用FEM有限元软件建立了套管井和相控声源的二维模型,计算了点声源和相控线阵声源在套管井中的声压波形。计算结果发现当控制相控线阵阵元间延迟时间使其辐射主声束偏转角满足地层纵波发生临界折射时,可以明显增强地层波幅度,即使在I界面或II界面胶结不好时也可观测到地层波,因此利用相控线阵声源的强穿透性可以帮助我们在套管井胶结不好的情况下探测地层。     

Detection performance of a diffusive wave phased array

Diffusive wave phased arrays have been demonstrated to be a sensitive method of detecting inhomogeneities embedded in heavily scattering media. However, the increase in sensitivity is coupled with an increase in noise, so that the optimum performance may not be obtained when the sources are modulated in antiphase. The performance of a range of configurations in the presence of Gaussian noise is investigated by using probabilistic detection theory. A model of diffusive wave propagation through scattering media is used to demonstrate that the phase performance can be improved by controlling the relative phase difference between the two sources. However, the best performance is obtained by using the amplitude response of a single source system. The major benefit of a phased array system is therefore the rejection of common systematic noise.     

Digital phased array beamforming using single-bit delta-sigma conversion with non-uniform oversampling

Digital beamforming based on oversampled delta-sigma (ΔΣ) analog-to-digital (A/D) conversion can reduce the overall cost, size, and power consumption of phased array front-end processing. The signal resampling involved in dynamic ΔΣ beamforming, however, disrupts synchronization between the modulators and demodulator, causing significant degradation in the signal-to-noise ratio. As a solution to this, we have explored a new digital beamforming approach based on non-uniform oversampling ΔΣ A/D conversion. Using this approach, the echo signals received by the transducer array are sampled at time instants determined by the beamforming timing and then digitized by single-bit ΔΣ A/D conversion prior to the coherent beam summation. The timing information involves a nonuniform sampling scheme employing different clocks at each array channel. The ΔΣ coded beamsums obtained by adding the delayed 1-bit coded RF echo signals are then processed through a decimation filter to produce final beamforming outputs. The performance and validity of the proposed beamforming approach are assessed by means of emulations using experimental raw RF data     

Finite-difference time-domain simulation of a liquid-crystal optical phased array

Accurate modeling of a high-resolution, liquid-crystal-based, optical phased array (OPA) is demonstrated. The modeling method is extendable to cases where the array element size is close to the wavelength of light. This is accomplished through calculating an equilibrium liquid-crystal (LC) director field that takes into account the fringing electric fields in LC OPAs with small array elements and by calculating the light transmission with a finite-difference time-domain method that has been extended for use in birefringent materials. The diffraction efficiency for a test device is calculated and compared with the simulation.     

相控阵天线的测试技术

介绍了相控阵天线的基本原理，并以线阵为例，给出了相控阵天线的方向图函数，由此导出线阵的波束指向、波束宽度、天线增益、波束零点、副瓣位置及副瓣电平等基本特性。针对相控阵天线的这些基本特性，提出了对其进行测试的原理和方法。     

超声相控阵系统中PCI驱动开发研究

超声相控阵系统的数据传输速率很大程度上决定着其检测速度,因而在PCI总线的超声相控阵系统中,PCI驱动执行效率至关重要。详细阐述了利用Win Driver、Driver Studio和WDK(Windows Driver Kit)三种工具开发PCI驱动程序的方法及实现。在驱动效率和兼容性等方面上比较这三种不同的驱动开发方案。分析及测试结果表明,使用Driver Studio开发的驱动能够高速稳定地工作,满足超声相控阵系统对于数据传输速率和稳定性的要求。由于不同的应用有着不同的开发需求,提出根据特定的开发需求选择不同的开发方案,从而得到需要的驱动及其应用程序。     

曲轴R区域超声相控阵检测方法研究

针对曲轴结构复杂的特性,开展超声相控阵技术在某型曲轴R区域检测中的应用研究。首先,建立曲轴R部位的声束覆盖模型,研究超声相控声束对曲轴R部位的覆盖及反射特点;然后,用超声相控阵方法对曲轴R区域进行检测实验,采用弧面楔块,改善声耦合效果;用VB编写的辅助检测软件,对回波信号进行定位和分析。实验对象为带人工缺陷的三拐曲轴,利用相控阵多角度声束扫查功能对其进行检测,将相控阵系统得到的回波信号数据输入辅助软件对缺陷进行定位,其定位绝对误差2 mm,并且缺陷位置显示直观,有利于判别。实验研究结果表明:利用超声相控阵成像技术和辅助检测软件相结合的手段有助于曲轴R区域缺陷的快速检测和准确评价。     

相控聚焦超声与圆孔交互作用的散射特性研究

相较于传统超声检测,相控阵技术的声束聚焦控制能力使得相控超声检测的分辨率、信噪比和灵敏度等性能得到有效提升。但针对相控超声与缺陷的交互作用认识不足,导致目前检测技术无法对缺陷进行准确定性和精确定量。为此,建立了一维线阵相控超声检测圆孔缺陷的有限元模型,重点研究相控聚焦波束与圆孔缺陷交互作用的声场散射特性。结果表明,圆孔散射L模态的能量主要集中于正反射区和正透射区,且在透射区的能量大于反射区的能量,而在与入射声束垂直的方向上能量极其微弱,几乎没有散射能量;散射L模态沿入射方向呈轴对称分布;对于不同直径的圆孔缺陷,直径越大,在相同方向上散射波的能量越大;对于相同直径的圆孔,聚焦波与平面波入射时,散射波的分布规律相同,但聚焦波散射的能量明显高于平面波入射时散射的能量。     

Coupled structural-electromagnetic-thermal modelling and analysis of active phased array antennas

The electromagnetic performance of an active phased array antenna (APAA) is obviously degraded because of structural distortion caused by thermal power consumption and exterior load. The coupled structural-electromagnetic-thermal (SET) model of APAA is developed on the analysis of the phase difference of radiating elements in the aperture field caused by structural displacement including load-displacement and thermal distortion of structure. Based on the cascade coupled finite element analysis of antenna structure, thermal distortion and other structural distortions are obtained. The coupled SET model is verified by analysing the degradation of the electromagnetic performances of a planar hexagonal APAA operating under different temperature distributions and structural constraints.     

Metric tensor approach to surveillance analysis of phased array radar

The author shows that the metric tensor gab is sufficient to accurately derive some of the most important system surveillance characteristics of static and rotating phased array radars. The author presents a novel and generalised method using metric spaces on Riemann manifolds as a viable approach for investigating phased array radar system design characteristics that is mathematically tractable and avoids complex iterative and non-analytic procedures.     

Functional properties of microstrip Si detector structures with implanted p-n junctions

The basic properties of microstrip Si detector structures with p-n junctions and the technological procedures for their production are described. Some results of manufacturing strip detectors with 200 μm and 20 μm strips are presented.     

Beam shaping with limited amplitude weight values for satellite active phased array antenna

针对星载DBF有源相控阵天线发射波束赋形的实际需要,提出了一种基于有限幅度加权的波束赋形方案。采用双重编码遗传算法实现了该方案。分别采用有限位长度的二进制编码和实数编码对阵列加权矢量的幅度和相位进行编码,使得阵列加权矢量的幅度仅在几个离散的台阶上变化,限制了阵列加权矢量幅度的动态范围,该方案在方向图旁瓣和功率放大器的效率之间取得了折衷,更适合于实际应用。与复数编码遗传算法相比,在保持最优解的精确度的同时,由于幅度维上搜索空间的减小,加快了算法的收敛速度。为了进一步提高算法收敛速度和避免算法“早熟” ,提出了一种基于”物种多样性“选择保留策略,并对算法采用了自适应交叉和变异概率,使算法更有把握得到全局最优或准最优解。     

Far field intensity of a partially locked optical phased array

The effects of imperfect frequency locking on the performance of an optical phased array were investigated. An analytic expression was obtained for the far field intensity pattern in terms of the degree of mutual coherence between lasers. The results of the analytical study were applied to determine the Strehl ratio of an injection coupled optical phased array for different degrees of slave resonator length control, ratios of injected to slave laser intensities, and pulse durations.     

柔性相控阵动态聚焦理论与仿真

曲面构件被广泛应用在各个领域的关键部位,一旦出现质量问题将造成不可估量的后果,为确保曲面构件在服役期间安全可靠,对其定期进行无损检测尤为重要。因超声相控阵技术检测灵敏度高、速度快,适用于曲面构件的快速检测,特别是柔性相控阵换能器的成功研制满足了复杂曲面构件的检测需求,但目前仍缺乏相应的理论支撑。因此,提出了复杂曲面柔性相控阵动态聚焦理论,并建立有限元声场时域仿真模型。结果表明,基于所提出的聚焦理论,采用柔性相控阵换能器可解决复杂曲面构件内部微小缺陷检测难题,为柔性相控阵换能器参数设计提供了理论依据,推动了柔性相控阵换能器的应用与发展。     

超声相控阵回波信号相位偏差的研究

在相控阵超声检测技术中,系统检测分辨率是系统性能的重要指标。影响该指标的因素是相控精度,即超声发射相控偏转聚焦与接收相控偏转聚焦的精度。但是在声束相控发射与接收的过程当中,检测材料以及检测系统等方面存在的扰动因素引起了超声检测信号的相位偏差。通过对造成检测信号产生相位偏差原因的具体分析,给出了偏差信号的模型,同时仿真研究了相位偏差对检测效果造成的影响。结果证明由于检测信号相位偏差的存在,系统的信噪比大大降低,系统性能下降。