SAW滤波器简化衍射频响的计算方法

提出了由一个变迹ＩＤＴ叉指换能器和一个均匀ＩＤＴ组成的ＳＡＷ滤波器简化衍射频响的计算方法，即将均匀ＩＤＴ简化成单根指计算其衍射频响。该方法与未简化衍射频响的计算方法相比，计算量大为减小，前者约为后者的（Ｎ为均匀ＩＤＴ的指对数）。并给出了一个实例，用未简化与简化方法分别计算了其衍射频响，结果表明，两者符合得较好。     

离散傅里叶变换在SAW滤波器衍射补偿中的应用

在Fresnel积分和各向异性抛物线近似下,用δ函数模型分析了由一个变迹IDT和一个均匀IDT组成的声表面波(SAW)带通滤波器衍射频响的计算方法,推导了滤波器采样频响的离散傅里叶反变换与变迹IDT叉指交叠长度序列的对应关系,并根据衍射频响和理想频响的差值计算出需要修正的变迹IDT叉指交叠长度序列的大小,通过迭代校正对衍射效应进行补偿。数值仿真结果表明,由衍射效应引入的滤波器频响带外恶化基本得到消除。     

多对叉指换能器耦合波型的分析

本文主要目的是详细地研究使用数百对乃至千对的多对叉指换能器的表面声波谐振器,并阐述多对典型叉指换能器的理论分析结果。在多对叉指换能器中,由电极指所产生的周期扰动对叉指换能器的特性影响极大,如本文中考虑到周期扰动的影响,则根据耦合波型理论进行分析,叉指换能器中的表面波与自由表面中的前进波和后退波近似一次结合,其结果可求出叉指换能器的 S 参数和表面声波谐振器的频率特性。例如,计算了 ST 切割的晶体基片上的多对叉指换能器的输入阻抗和传输特性,表明与实验结果完全一致。而且与此结果比较,晶体基片上的多对叉指换能器中的电极指的声周期扰动对叉指换能器特性的影响是很明显的。     

体声波宽带声光偏转器

本文给出了体声波宽带声光偏转器的计算和实验研究结果。体声波是借助于叉指换能器这一简便方法激励的。结果表明,在给定的叉指换能器周期和指对数条件下,可获得最佳的偏转器频带,在此频带内可得到最大衍射效率。经对该偏转器的工作进行分析表明,这种器件能成功地运用于射频信号的频谱分析和匹配滤波,并可作光计算机中的线性代数处理用声光处理器。     

声表面波式小波变换处理器衍射问题的研究

传统声表面波式小波变换处理器存在衍射问题。该文通过改变叉指换能器结构的方法解决衍射问题,即输入换能器存在衍射问题区域的指条采用宽度加权;不存在衍射问题的区域结构不变。推导了实现新结构无衍射问题的声表面波式小波变换处理器的函数关系。在压电基片材料X-112°YLiTaO3上设计和制作了尺度2-1和2-2两种声表面波式小波变换处理器样品。通过数值计算和测量,论证了新结构声表面波式小波变换处理器不存在衍射问题。     

ZnO—SiO2—Si层状结构中叉指换能器的声体波激励研究

当叉指换能器在基片上激励声表面波模式时，同时伴随有声体波的激励。文章根据已有的叉指换能器声体波激励理论，对层状结构ＺｎＯ－ＳｉＯ２－Ｓｉ中叉指换能器的声体波激励进行了研究，通过计算表面有效介电常数εｅｆ（ｓ）的虚部，得到了声体波的激励强度与层状结构参数之间的定量关系。文中所采用的分析方法，适用于其他层状结构中叉指换能器的声体波激励研究     

基于LCP基板的平面叉指电容研究

平面叉指电容作为电路系统中的重要器件,对电路性能影响极其重要。本文在50μm厚度双面覆铜的液晶聚合物(Liquid Crystal Polymer,LCP)基板上加工了多款平面叉指电容,系统研究了平面叉指电容的叉指长度、宽度和间距的变化对其电容值的影响规律。结果表明:叉指长度从3 mm增加到4 mm,叉指电容容值增加1.63 pF;叉指宽度从0.2 mm增加到0.3 mm,叉指电容容值增加2.35 pF;叉指间距从0.1 mm增加到0.2 mm,叉指电容容值减少0.75 pF。通过集总参数等效,建立了平面叉指电容的等效电路,分析了等效电路中集总器件和不同平面叉指电容物理结构参数的对应关系,为LCP工艺中电容的设计提供了技术参考。     

GHz级SAW滤波器的实现—双谐频叉指换能器

为了提高叉指换能器的工作频率和克服亚微米工艺带来的困难，科研工作者提出许多不同的设计方法。在１９９５年的《准谐频叉指换能器》一文的成功设计方法的基础上，我们进一步改进提出了双谐频叉指换能器ＤＨＩＤＴｓ的设计方法，使得工作频率同时处于元因子和阵因子的谐频上。由于其更宽的指条宽度，更好的旁瓣抑制性能和低损耗，使之更适合于高频ＳＡＷ器件。本文给出了双谐频叉指换能器的设计过程，理论计算与实验结果，表明理论     

柔性基底印刷叉指电容的阻抗特性研究

为降低电容制作成本,采用丝网印刷的方式在柔性PET基底上印制出可用于较高频段范围的叉指电容。首先利用电磁仿真软件设计出叉指电容的结构;然后通过实验研究了工艺参数对印刷薄膜电阻值的影响和油墨种类对印刷叉指电容阻抗特性的影响,确定合适的丝网印刷工艺参数和导电性能良好的油墨;最后,采用上述油墨和工艺参数印制了不同结构参数的叉指电容,测试了其阻抗特性,分析了不同结构参数对其阻抗特性的影响。实验结果表明:印刷叉指电容的阻抗特性与理论仿真结果一致;叉指电容所有结构参数中,指的长度和指的个数对其阻抗特性影响较大,印制的叉指电容在100~600 MHz范围内具有较好的阻抗特性。     

声表面波式指宽变长小波变换处理器的设计

为消除声表面波式小波变换处理器压电基片对频率特性的影响,以及输出换能器的指条数对带宽的影响和解决衍射问题,研制了声表面波式指宽变长小波变换处理器。该处理器选取机电耦合系数为0.64%的X-112°Y LiTaO_3压电基片,输出换能器指条数为36,输入换能器采用指宽变长且声孔径均匀的叉指换能器。设计和制作了尺度2-2声表面波式指宽变长小波变换处理器样品。实验结果表明,声表面波式指宽变长小波变换处理器频率特性曲线光滑,-3dB实验带宽为1.072 MHz,与理论带宽值一致,且不存在衍射问题。     

全息照片的显微结构

文章披露了全息光栅，散射物体的离轴全息和彩虹全息图片，在５０００倍扫描电子显微镜下的照片。并从理论上解决了它们的显微结构。指出它们是散射在体干版上的菲涅尔变换频谱与参考光相干淑的结果。旨出这种显微结构是散射物体全息照片衍射效率低于全息光栅的根本原因，并提出了改进拍摄办法，以增加衍射效率。     

散射物体全息照片的显微结构与拍摄参数的选择

文章披露了全息光栅，散射物体的离轴全息和彩虹全息图片，在５０００倍电子显微镜下的照片，并从理论上解释了它们的显微结构。指出它们是散射物体在干板上的菲涅尔变换频谱与以考光相干涉的结果。指出这种显微结构是散射物体全息照片衍射效率低于全息光栅的根本原因，并提出了改进拍摄办法。以增加衍射效率和提高信噪比。     

Comparative study of lateral profile knife-edge diffraction and raytracing technique using GTD in urban environment

In an urban environment, radio wave interaction with buildings may affect considerably the propagation of radio waves, mainly because of multipath, diffraction, and shadowing effects. This paper outlines the effect of two-dimensional (2-D) (vertical and lateral) diffraction and compares a Fresnel-Kirchhoff scalar approach to a vectorial geometrical theory of diffraction (GTD) approach applied to a four-ray system. The former can be considered as a generalization of conventional knife-edge diffraction theory while the latter (GTD) is useful in the context of ray tracing. A very good agreement between the Fresnel-Kirchhoff and GTD results is found within the limits of validity of both methods. Moreover, it is shown that conventional knife-edge diffraction theory can largely overestimate attenuation (10-15 dB) behind tall buildings in the center of a city environment. Different frequency bands have been tested for the sake of comparison, and emphasis has been put on the radio communications frequency bands used for the global system for mobile communications (GSM) and DCS/DECT systems at 900 and 1800 MHz     

One watt average power by second harmonic and sum frequencygeneration from a single medium scale copper vapor laser

Ultraviolet (UV) powers of over 1 W have been obtained by second harmonic and sum frequency generation from a single medium scale (20 W) copper vapor laser (CVL) using a new focal geometry in which the CVL beam is focused in only one direction to produce a line focus within a BBO crystal. High optical conversion efficiencies, 20 and 30%, are observed for the low divergence (~-10 times the diffraction limit) and diffraction-limited components of the CVL output, respectively. Wall-plug efficiencies for UV generation are up to 0.04%. Efficient frequency conversion has also been demonstrated for CVL operating conditions unsuited to the generation of diffraction limited output     

Rectangular microstrip patch antennas with infinite and finite ground plane dimensions

The rectangular microstrip patch antenna has been extensively analyzed with regard to its input impedance and resonant frequency, both for infinite and finite ground plane dimensions. For infinite ground planes existing formulas have been compared and improved parameters presented. The influence from the side current radiation has been discussed as well. For finite ground plane dimensions the contribution from the ground plane edge diffraction has been accounted for in an equivalent radiation conductance and an equivalent diffraction susceptance. Formulas for these parameters have been developed on the basis of different theories. They are valid under the condition that only one of the ground plane dimensions are finite at the same time. Experimental investigations are carried out to test the accuracy of the developed formulas, showing good accuracy under the given conditions.     

激光衍射法测量表面波的衰减系数与频率的关系

对于频率为几百赫兹的液体表面波,实验上观察到稳定、清晰、反衬度非常高的衍射图样.理论上得到了衍射条纹间距、表面波波矢量与衰减系数之间的解析关系,并建立了表面波衰减特性的检测方法和实验装置.观察到表面波的衰减效应及衰减系数的色散效应,结果表明衰减系数随频率几乎成线性关系,与理论值吻合.     

激光衍射法测量液体粘滞系数

对频率为几百赫兹的低频液体表面波,当激光束照射在表面波上,可以产生清晰的光衍射效应.基于这种低频液体表面波的光衍射效应,提出了一种测量液体粘滞系数的光学方法.理论上导出了粘滞系数与表面波衰减系数和表面波波矢量之间的解析关系,进一步给出表面波衰减系数和波矢量与衍射图样的关系;实验上给出了测量装置,观察到高清晰稳定的液体表面波衍射条纹,衍射图样随表面波传播距离的变化,衍射条纹强度随表面波传播距离的变化,得到了表面波衰减曲线,最后测得水的粘滞系数为(0.746±0.0195)×10-3N*m/s2,与传统的毛细管法相比,本方法具有实时、无损、非接触的优点.     

减小声光频谱仪频率测量方差算法研究

声光器件衍射光峰值偏转位置与输入信号频率成正比是声光频谱仪测频的基本原理,但实际中衍射的非线形效应会引起衍射光峰值偏转误差较大。为减小频率测量方差,需对衍射光强数据做相应处理。对CCD背景噪声的数字特征分析,以背景噪声数学平均值为阈值做去噪处理。根据最小二乘法原理,对衍射光强数据做一次高斯函数拟合,拟合数据与光强数据相关系数为0.997 6。在现有测试光学平台下,根据衍射光强峰值位置估计的频率测量方差为542.5 kHz2,利用拟合高斯函数中心值估计的频率测量方差为31.8 kHz2。为减小声光频谱仪频率测量方差提供了理论支持。     

Integrated magnetooptic Bragg cell modulator in yttrium irongarnet-gadolinium gallium garnet taper waveguide and applications

An integrated magnetooptic (MO) device which consists of an ion-milled collimation-focusing lens pair and a guided-wave MO Bragg cell modulator in a yttrium iron garnet-gadolinium gallium garnet (YIG-GGG) taper waveguide substrate with dimensions of 6.0×16.0 mm ² has been realized for the first time. Performance characteristics of the waveguide lenses including the focal spot size, sidelobe level and throughput, and that of the integrated MO Bragg cell modulator using the magnetostatic forward volume wave (MSFVW) at X-band carrier frequency including the bandwidth, diffraction efficiency, dynamic range, and frequency resolution have been measured at the optical wavelength of 1.303 μm. Scanning of the focused diffracted light beam by varying the carrier frequency of the MSFVW and RF spectral analysis by simultaneous application of multiple microwave frequencies have been demonstrated     

Site shielding of earth-station antennas

This paper concerns interference in satellite earth stations, due to microwave links sharing the same frequency band, and its solution by site shielding. The uniform theory of diffraction (UTD) has been used to analyze the near field of a parabolic-reflector antenna. An extension of the UTD, in which the influence of the surface impedance is taken into account, has been applied, to calculate the diffraction from the top of the barrier. The theoretical model has been verified in a field-measurement exercise, using a three-meter earth-station antenna, located behind an existing free-standing concrete wall, with a simulated source of interference. The undesirable effects of the barrier on the gain, noise temperature, and the radiation pattern have been studied, and criteria for the clearance of the main beam have been established. Methods of improving shielding effectiveness using absorbing materials and, also, specially shaped diffracting edges have been studied, as well. Laboratory measurements of the diffraction loss of absorbers have been made, and relative advantages are presented. Design guidelines have also been given