Experimental verification of the effect of aperture shape on prompt IRA response

This article presents experimental measurements verifying the relationship between aperture shape and prompt response in an impulse radiating antenna (IRA). Various aperture configurations were realized by constructing a lens IRA with focusing aperture significantly larger than the transverse electromagnetic (TEM) feed structure and then eliminating portions of the aperture with metal blocks. Virtually any prompt response can be realized by a suitable construction. Experimental results agree well with predictions made by evaluating the aperture integral of the TEM mode distribution.     

Effect of defocus on the prompt response of a reflector IRA

Impulse radiating antennas (IRAs) are an emerging class of antenna that are designed to radiate extremely short electromagnetic pulses with multiple decades of instantaneous bandwidth. The most common IRAs are made with a transverse electromagnetic (TEM) transmission line feeding a paraboloidal reflector. The IRA is usually constructed so that the electrical feed point of the TEM transmission line coincides with the focal point of the paraboloid. The paraboloidal reflector converts the spherical wave emanating from the feed point into a plane wave (i.e., a spherical wave centered at -/spl infin/). In many practical cases, the feed point and focal points are not exactly aligned, producing some defocus of the reflector. In this paper, we model the case of hyperbolic defocus because of its analytic form and compare this model with experimental measurements. A hyperboloidal reflector fed from one focus converts the expanding spherical wave into a second expanding wave which appears to emanate from the second focal point of the hyperboloid (which is behind the reflector). Hyperboloidal defocus is roughly equivalent to moving the electrical feed closer to the reflector than the optical focal point. Previous theoretical results from in-focus IRAs predicted that the E- and H-plane temporal responses should be symmetric with respect to the temporal center of the response. The results shown here demonstrate that the defocusing causes these responses to become asymmetric. The new results are in better agreement with experimental measurements of IRAs and provide a physical explanation for experimental results that differ from the original theory.     

Improvement of prompt response from impulse radiating antennas by aperture trimming

Reflector impulse radiating antennas (IRA) traditionally have been constructed by terminating a self-reciprocal, transverse electromagnetic (TEM) transmission-line feed structure into a paraboloidal reflector. The section of the paraboloid used is usually circular in cross-section, with the outer boundary coinciding with the circle of symmetry of the TEM feed. The reflector converts the spherical TEM mode on the feed line into an approximate plane wave in the near field by geometric optics. The prompt radiated electric field in the direction of focus is given in the physical optics approximation in terms of the integral of the electric field of the TEM mode over the aperture plane inside the reflector boundary. Balanced feed structures have TEM modes that provide both positive and negative contributions to this integral in the aperture plane. Determination of the contour where the principal component of the electric field in the TEM mode is zero identifies portions of the aperture that contribute destructively to the integral. These portions are removed, thereby increasing the prompt radiated field without altering the feed structure or the applied voltage waveform. Furthermore, decreasing the size of the TEM feed relative to the aperture size, followed by appropriate aperture trimming, allows an even greater increase in radiated field. Results are presented that predict an increase in prompt radiated fields for all electrode configurations. Improvements are largest for electrode angles that are large (with respect to the vertical). The trends predicted by the numerical results are verified by an experiment conducted on a time-domain antenna range.     

大数值孔径介质结构透镜

提出了一种新型大数值孔径介质结构透镜,能量利用率达到了44%。通过数值仿真FDTD计算证明该聚焦器件能实现高的能量利用率和接近衍射极限的聚焦光斑,且聚焦光斑的旁瓣很小。其次,对该透镜的色散性能进行了研究,发现该透镜具有与普通透镜相反的色散特性。故该透镜可以与普通透镜组合消色差。另外,该透镜克服了最小特征尺寸,实现了大数值孔径,针对波长10.6 m设计了相同口径、不同F数的介质结构透镜,最小F数达到了0.25。     

以霍尔电流传感器提高开关电源的效率

许多开关电源中需要使用电流传感器,将电流大小以电压形式反馈至开关电源控制器,用以调节输入脉冲的占空比或进行电源保护。以往的开关电源往往使用一个串入电流通道的电阻作为电流传感器,利用电阻的压降反馈电流的大小。由于电阻是耗能元件,其将产生功耗。为克服电流传感电阻的功耗,本文采用霍尔传感器作为开关电源的电流传感器,并详细论述了霍尔传感器在开关电源中的设计使用方法。霍尔传感器的使用大大降低了因电流检测而产生的功耗,提高了开关电源的转换效率。     

如何提高非线性编辑的工作效率

视音频非线性编辑系统 (Ｖｉｄｅｏ＆ＡｕｄｉｏＮｏｎ -ｌｉｎ ｅａｒＥｄｉｔｉｎｇＳｙｓｔｅｍ简称非线性编辑 )以低成本、高效率、高质量进入广播电视领域 ,对传统的线性编辑造成了极大冲击 ,面临制作方式的变革也给许多电视从业人员带来了新的机遇和挑战。目前 ,国产的广播级非编系统都是基于加拿大Ｍａｔｒｏｘ公司的Ｄｉｇｉｓｕｉｔｅ系列套卡开发的 ,很多系统都能完成同一项任务 ,我们关注的是在现有的硬件和软件条件下 ,如何高质量、高效率地完成节目制作任务。1　编辑前的准备工作对单机非编用户来说 ,除了一套非编系统外 ,最好…     

提升AOl检测PCB效率的方法研究及应用

随着PcB的高多层化发展的需要,制程中广泛应用AOI设备进行图形质量检测,如何提升昂贵的AOI设备的使用效率,成为PcB生产中的一个重要课题。简要介绍根据AOI设备检验的原理规则,通过对AOI设备光学系统的技术改良,提升AOI设备对图形电镀亮板和全板电镀暗板等特殊材料板的检测能力,大幅改善AOI设备的检测效率,节约了PCB生产中的检验成本和流程时问,取得显著的应用实效。     

A method to improve the efficiency of CMP process

There are two important things when doing the CMP, one is the high removal rate, and the other is low nonuniformity. The factors, which may effect the result of polishing process, are pressure applied to wafer and the rotation speed of the wafer. In this study, the best polishing pressure distribution was studied. The effect of different boundary conditions between wafer and wafer carrier on the polishing pressure distribution was analyzed. The clearance between pad and wafer also analyzed     

Spectral switching of Gaussian-Schell model beams passing throughan aperture lens

Starting from the propagation equation of partially coherent light, the spectral switching of Gaussian-Schell model (GSM) beams passing through an aperture lens is studied. Our detailed theoretical and numerical results have shown that the spectral switching of GSM beams is mainly dependent on the truncation parameter, coherence parameter and Fresnel number. By a suitable choice of the system parameters, the position, number, and transition amplitude of the spectral switch can be varied     

厄米双曲余弦高斯光束通过光阑透镜的位相奇点

对厄米双曲余弦高斯光束通过光阑透镜的位相奇点进行了研究。数值计算结果表明截断参数δ和离心参数b都会影响厄米双曲余弦高斯光束通过光阑透镜的位相奇点分布。随着截断参数的增大,通过光阑透镜的厄米双曲余弦高斯光束的位相奇点发生产生和湮灭,在整个过程中总的拓扑电荷守恒。当b≤0.97时,奇点A,B互相靠近而湮灭;0.97相似文献   

高分辨率大孔径手机镜头设计

为了满足目前人们对手机镜头的大孔径和高分辨 率的要求,本文在几何光学理论基础 上,应用光学设计软件Zemax设计出一款1300万 像素手机镜头。在设计中采用扩展奇次非球面来校正系统像差。该镜头由4块 扩展奇次非球面镜片和1块滤光镜片组成,结构简单紧凑;它的F数为2.17,全视场角为 73.2°,有效焦距3.93 mm,镜头总长6.00 mm;最终实现中心视场在中间频 率处(即223 lp/mm)的子午和弧矢方向MTF值分别大于 0.33,在高频处(即446 lp/m m)分别大于0.13;另外,0.8视场在中间频率的子午和弧矢MTF值分别大于0.33,研究表明优化设计后的手机镜头 成像效果完全可以满足使用要求。     

利用LDO改善白光LED的匹配度

白光LED与荧光灯相比具有使用简单、成本低的优势,与白炽灯相比可以提供真正的白色光,因此,其用量在最近几年呈现出稳步上升的趋势,在手持式产品中被广泛用作闪光灯、显示器背光等。当然,在实际应用中针对白光LED也存在一些有待解决的技术问题。 选用白光LED最明显的问题是产品的匹配性差,按照白光LED的典型规格,电流为20mA时正向电压的最小值为3.0V、典型值为3.5V、最大值为4.0V。显然,稳压源不是合理的解决方案。当然,利用相同的电流驱动每只LED可以获得均匀亮度,但成本很高。在许多应用中只是简单地用一个固定偏置电压和镇流电阻驱动LED,如图1所示。     

Method to improve thermal poling efficiency in silica glasses

For the first time, thermal polings are performed on Suprasil I samples (Heraeus) under square alternating voltages at variable frequency. Experimental results exhibiting a large increase (×13 compared to a continuous voltage poling) of the second-harmonic signal generated within a sample poled at a frequency of 1 mHz are presented     

引用新技术提高用电检查效率

随着我国经济的迅速发展,人们对用电的需求也越来越高,因此需要加强安全用电的意识,提高用电检查效率。管理好用户如何用电,这个问题不仅仅与用户用电安全密切相关,而且还关系到供电企业的形象以及管理水平。本文从用电管理工作的重要性、用电检查工作存在的问题以及利用新技术提高用电检查效率三个方面进行详细论述。     

浅析如何提高变电倒闸操作效率的措施

变电倒闸是电力操作中的关键部分,同时它也是电力稳固运行的前提与保障.所以,本文针对变电倒闸操作中的一些问题,对如何提高倒闸操作效率提出建议.     

用D类放大器提高音频放大效率

D类采用脉宽调制(PWM)信号取代AB类放大器通常采用的线性信号。PWM信号包括音频信号以及PWM开关频率与谐波。D类音频放大器比AB类放大器效率高得多,因为输出MOSFET可从极高阻抗转变为极低阻抗,从而在作用区操作只有几纳秒。利用上述技术,输出级上损失的功率极低。此     

T300扫描电镜物镜光阑加热电路故障与维修

为了防止物镜光阑污染，T300扫描电镜在高真空状态下，物镜光阑加热电路给物镜光阑加热，以免造成其污染。由于观察样品时，电子束通过物镜光阑孔，因此要求物镜光阑加热电路保持稳定输出电流和电压，否则将会造成图像不稳。     

平顶高斯光束通过光阑透镜的焦移

从Collins公式出发,研究了平顶高斯光束通过光阑透镜的焦移,并用大量数值计算例予以说明。研究表明,截断平顶高斯光束的焦移不但由光束的阶数N、光束菲涅耳Fw决定,还与孔径菲涅耳数Fa有关。与无光阑情形比较,对于光阑透镜,即使在Fw很大的情况下,仍然存在焦移。     

不同空间分布光束通过聚焦光学系统传输特性的比较

基于柯林斯公式和ABCD传输矩阵理论，在相同激光功率和初始束宽下，研究了不同空间分布光束通过聚焦光学系统的传输特性，结果表明，入口处不同阶次的超高斯光束在距离光学系统焦点一半的位置（z=f/2)，光强分布的差别很大，轴上光强随着阶次的增加，先增加，然后减小至固定值；聚焦光学系统入口处超高斯光束的阶次越大，即光强分布越均匀，在光学系统的焦点位置（z=f)，光轴上激光强度越大，直至趋于固定值，但光强分布的差别不大。     

Shaping of subreflectors in cassegrainian antennas for maximum aperture efficiency

This paper describes a systematic technique for obtaining high aperture efficiency in a Cassegrainian feed system by special shaping of the subreflector. Theoretical expressions are derived that determine the subreflector shape, which gives a uniform illumination of a paraboloid for a given primary feed pattern. Experimental data are then presented, which demonstrate the enhanced performance of a Cassegrainian feed system using a subreflector shaped according to the theoretical expressions.