1891_车厢自动调平机构的研究和设计
1891_车厢自动调平机构的研究和设计,车厢,车箱,自动,机构,研究,钻研,以及,设计
黄河科技学院毕业设计(文献翻译) 第 1 页原文:Very Large Scale Integrated Circuit TechnologyThe future of high performance digital and analog signal processing subsystems for radars will be closely intertwined with the tremendous advances in semiconductor integrated circuit technology. VLSI chips are capable of combining over 100000 devices on a single chip of silicon.A 250 megahertz bipolar random access memory (RAM) is designed by Hughes Radar System Group. To demonstrate the density of a VLSI chip, this would have the equivalent density of the VLSI wafer with a minimum feature size of o.5 micrometer. The small size of the features on the VLSI chips allow tens of thousands of computer circuits to be put on one chip.VLSI chips will be used to develop radar signal processors with throughputs of over 1 billion computations per second (1 gigahertz)! These special purpose computers are designed to carry out computations on algorithms which in turn derive information from the radar return or echo. Higher throughput allows the radar to detect objects at longer ranger with ever more accurate tracking and enhanced mapping functions.The development of advanced signal processing computers requires a highly integrated approach involving many disciplines. The VLSI chips which will form these processors are themselves small systems which would normally require many men-years of engineering to complete. Powerful computer-aided design (CAD) systems are being developed which allow the entire chip operation to be simulated to assure correct operation, then guide the engineer through a series of programs to a complete chip design with the errors. In addition, new ultra high speed test systems are being developed which receive their test programs from the central CAD system. The development of these CAD and test systems is s challenge comparable to the design of the chips themselves. 黄河科技学院毕业设计(文献翻译) 第 2 页Analog-to-Digital Converter (ADC)An analog-to-digital (ADC) is a device that converts a signal that is a function of a continuous variable into a representative number sequence. Typically, an ADC consists of a sampling unit, a quantization unit, and an encoding unit (as shown in Fig C40).AnlogWavefrmSpi UtQuanzoEcdig UtDalCeF.40-vrFormats. The most frequently used digital format is the power-of-2 binary forms: E=k(bN2N-1+bN-12N-2+bN-22N-3+b120 Where E=analog voltageN=number of binary digits Bi=state of the binary digitThe encoded word usually is applied to a general-purpose computer in serial form, but is applied to special-purpose high-speed computer in parallel form. The Grey code is used in certain of asynchronous converters where encoded data is read out of the converter continuously. This code allows all adjacent transitions to be accomplished by the change of a singly digit only. Use of the Grey code greatly reduces the magnitude of transient errors in such cases.Converters in radar systems normally have a complemented power-of-2 format for negative inputs. This simplifies both the converter and subsequent and subsequent computations. In the complemented format, the converter counts up form the most positive value to zero and then continues to count up form zero to the most positive 黄河科技学院毕业设计(文献翻译) 第 3 页value. A sign bit indicates which half of the range applies.Applications. Analog-to-digital converters find numerous applications in modern radar systems. The trend toward processing of radar data has resulted in a demand for fast converters that are able to convert date in ream time.Digital MTI is an example of technique requiring such high-speed converters. Here, the synchronous-detector output is sampled at a rate not less than the receive bandwidth, and the digital result is stored in a large digital memory. Data is read form the memory to allow comparison with corresponding returns form subsequent radar “looks”. The flexibility of this method has permitted MTI velocity response characteristics previously unobtainable with analog memory devices.Many tracking radars use a converter to encode the echo in the tracking gate. In this case, a general-purpose computer provides all computer all computations required to track a target and to provide range and velocity outputs. Precise data-smoothing and stabilizing characteristics are provided by the computer.High-speed converters have been used to encode the height information form a stackedbeam radar.Another application of converters is in the field of digital recording. This is used where cast quantities of data are to be analyzed or where an isolated event is to be analyzed. In this case, the encoded data is stored on magnetic tape. The results are then analyzed in non-real time with arithmetic accuracy. 黄河科技学院毕业设计(文献翻译) 第 4 页Radar AntennasThe basic role of the radar antenna is to provide a transducer between the free-space propagation and the guided-wave propagation of electromagnetic waves. The specific function of the antenna during transmission is to concentrate the radiated energy into a shaped directive beam which illuminates the targets in a desired direction. During reception the antenna collects the energy contained in the reflected target echo signals and delivers it to the receiver. Thus the radar antenna is used to fulfill reciprocal but related roles during is transmit and receive modes. In both of these modes or roles, its primary purpose is to accurately determine the angular direction of the target. For this purpose, a highly directive(narrow)beamwidth is needed, not only to achieve angular accuracy but also to resolve targets close to one another. This important feature of a radar antenna is expressed quantitatively in terms not only of the beamwidth but also of transmit gain and effective receiving aperture. These batter two parameters are proportional to one another and are directly related to the detection range and angular accuracy.The above functional description of radar antennas implies that a single antenna is used for both transmitting and receiving. Although this holds true for most radar systems, these are exceptions: some monostatic radars use separate antennas for the two functions; and, of course, bistatic radars must, by definition, have separate transmit and receive antennas.Radar antennas can be classified into two broad categories, optical antennas and array antennas. The optical category, comprises antennas based on optical principles and includes two subgroups, namely, reflector antennas and lens antennas. Reflector 黄河科技学院毕业设计(文献翻译) 第 5 页antennas are still widely used for radar, whereas lens antennas, although still used in some communication and electronic warfare (EW) applications, are no longer used in modern radar systems.RadomesRadomes are used when it is necessary to protect antennas from adverse environmental effects. Ldeally, a radomes should be perfectly transparent to the RF radiation form (or to) the antenna and yet be able to withstand such environmental effects as wind, rain, hail, snow, ice, sand, salt spray, lightning, and (in the case of high-speed airborne applications) thermal, erosion, and other aerodynamic effects. In practice, these environmental factors determine the mechanical design of the radome, and the desire for ideal RF transparency must be compromised because mechanical and electrical requirements are often in conflict.Radomes cause four major electrical on antenna performance. Beam deflection is the shift of the electrical axis which is critical for tracking radar. Transmission loss is the measure of energy lost by reflection and absorption. The reflected power causes antenna mismatch in small radomes and sidelobes in larger radomes. Secondary sffects include depolarization and antenna in small rsdomes and sidelobes in larger radomes. Swcondary effects include depolarization and antenna noise additions.Radome design is a specialized art, and many books are devoted to its intricate details. This section makes to attempt to provide radome design information as but instead is aimed at making the radar system designer aware of the basic concepts behind the types of radomes available for various applications.These are two main categories of radomes for radar antennas: radomes for ground-based or shipboard systems and radomes for airborne or missile. Although these two differ significantly in size and form, they have some general characteristics in common.Types of Radomoes and General Considerations. These general classes of radome are of interest: feed covers, which often have to endure pressure, high voltage, 黄河科技学院毕业设计(文献翻译) 第 6 页and heating; covers attached to the reflector, which alter the pattern in a fixed manner; and external radomes, within which the entenna moves. Within each class, a variety of skin and shin-supporting designs is available to minimize the electrical effects under the constraints of the environment. The radome skin may be sigid supported by a framework, or air-supported.The most common rigid radome-wall structures are known as homogeneous single layer, A-sandwich, B-sandwich, C-sandwich, multiple-layer sandwich and dielectrics with metal inclusions.Single Layer . The homogeneous single-layer radome has been used in many radome applications. Materials for this type have included fiberglass-reinforced plastics, ceramics, elastomers, and monolithic foam. The optimum thickness for a single layer is a multiple of a half wavelength in the dielectric material at the appropriate incidence angle, but many single-layer radomes are simply thin-wall approximations to the zero-thickness case.A-Sandwich. A commonly used radome-wall cross section is the A-sandwich, which consists of two relatively dense thin skins and a thicker low-density core. This configuration exhibits high strength-to-weight ratios. The skins are generally fiberglass reinforced plastics, and the core is a foam or honeycomb. Inorganic skin and core sand-wiches also have been developed for high-temperature applications. As a rule, the skins of the sandwich are made symmetrical or of equal thickness to allow midband cancel-lation of reflections.B-Sandwich. In contrast to the A-sandwich, the B-sandwich is a three-layer configuration whose skins have a dielectric constant lower than that of the core material. This wall cross section is heavier than that of the A-sandwich because of the relatively dense core. The B-sandwich is not commonly used because the core dielectric constant is quite high for a proper match.C-Sandwich. The C-sandwich is a five-layer design consisting of outer skins, a center skin, and two intermediate cores. The symmetrical C-sandwich can be thought of as two back-to-back A-sandwiches. This configuration is used when the ordinary A-sandwich will not provide sufficient strength, or for certain electrical performance 黄河科技学院毕业设计(文献翻译) 第 7 页characteristics, or when one layer is to serve as a warm-air duct for deicing.Multiple-Layer Sandwich. Multiple-layer sandwiches of 7, 9, 11, or more layers are sometimes considered when great strength, good electrical performance, and lightweight are required. Some of these designs have used thin layers of fiberglass laminates and low-density cores to attain high transmission performance over large frequency bands. Dielectric Layers with Metal Inclusions.Metal inclusions have been considered for use with dielectric layers to achieve frequency filtering, broad-frequency-band performance, or reduced-thickness radomes. Thin layers of metal inclusions exhibit the characteristics of lumped circuit elements shunted across a transmission line. For example, a grid of parallel metal wires exhibits the properties of a shunt-inductive susceptance. 黄河科技学院毕业设计(文献翻译) 第 8 页翻译为中文超大规模集成电路技术未来的高性能数字和模拟信号处理子系统雷达将密切交织在一起的巨大进步。超大规模集成电路芯片,可结合超过 100000的设备在一个硅芯片。 一个 250兆赫的双极型随机存储器(内存)是由休斯雷达系统设计组设计的。为了证明超大规模集成电路芯片的密度,这将需要有同等密度与最小特征尺寸的 o.5千分尺的超大规模集成电路晶片。小规模的功能上的超大规模集成电路芯片,允许成千上万的计算机电路放在一个芯片中。超大规模集成电路芯片将被用于开发吞吐量超过 1000000000每秒运算(1兆赫)的雷达信号处理器中!这些特殊用途的计算机通过设计好的算法经行计算,从而获取雷达回波或呼叫的信号。更高的吞吐量,使雷达探测在较长的游侠与以往任何时候都更准确的跟踪和映射函数。发展先进的信号处理电脑需要一个高度集成的方法,这将涉及许多学科。超大规模集成电路芯片,将形成这些处理器自己小的系统,通常需要很多 men-years工程完成。功能强大的计算机辅助设计(计算机辅助设计)系统正在开发,使整个芯片操作模拟保证正确的操作,然后指导工程师通过一系列的程序,一个在误差范围内的完整的芯片设计完成了。此外,新的超高速度测试系统正在开发,中央计算机辅助设计系统将接受他们的测试程序。发展这些计算机辅助设计和测试系统的挑战相比设计的芯片本身将要高出许多倍。 黄河科技学院毕业设计(文献翻译) 第 9 页模拟数字转换器(模数转换器)一个模拟数字(模数转换器)是一个转换装置的信号,是一个以功能可以连续变化为代表的数字序列。通常,一个模数转换器由采样单元,量化单元,和一个编码单元组成(如图所示变化) 。模 拟波 形 抽 样单 元 量 子 化单 元 编 码单 元 数 字t模 拟 数 字 转 换 器代 码格式,最常使用模拟数字的数字格式是 power-of-2二进制形式E=k(bN2N-1+bN-12N-2+bN-22N-3+b120 其中: E=模拟电压N=二进制数字的数目 Bi=二进制数字的状态编码字通常是用于通用计算机的串行形式,但也应用于专用电脑高速并行的形式。灰色的代码是用在某些异步转换器在不断读取数据的编码的转换中。这个代码只有允许通过改变一个单独的数字所有相邻数据的过渡。用灰色代码大大降低了在这种情况下的幅度瞬态错误。变频器在雷达系统通常有一个补充 power-of-2负输入的格式,这简化了转换器和后续的计算。在补充格式上,转换计数形式最积极的价值为零,然后继续从零开始计数到最积极的表明价值的一个标志位,这种情况可适用在一半以上的范围中应用程序,发现在现代雷达系统中有许多模数转换器的应用。雷达数据处理的趋势已导致需求可以在实时转换日期得快速转换器。 黄河科技学院毕业设计(文献翻译) 第 10 页数字动目标显示就是一个要求高速转换器技术的例子。在这里,synchronous-detector输出的采样速度不小于接收带宽,和数字结果存储在一个大的数字存储器中。数据读取的内存允许“看起来”与形成后的雷达相应的回报。他这种设计方法的灵活性允许线速度响应特性与以前无法得到的模拟存储器件。多雷达跟踪使用一个转换器编码中的回声跟踪门。在这种情况下,通用计算机提供所有计算机计算需要跟踪目标并提供范围和速度输出。精确的数字平稳性和稳定特性是由计算机提供的。高速转换器还被用于编码聚积束高度雷达的信息。另一个应用程序变换是在国外的数字记录。这是用在对铸造数量的数据进行分析中,或在对一个孤立的事件进行分析中。在这种情况下,编码的数据存储在磁带上。对结果进行分析,保持实时运算精度。 黄河科技学院毕业设计(文献翻译) 第 11 页雷达天线雷达是一种有源装置,它有自己的发射机而不像大多数光学和红外传感器那样依赖于外界的辐射。在任何气象条件下,雷达都能探测或远或近的小目标,并精确测量他们的距离,这是雷达和其他传感器相比具有的主要优势。而雷达传播和接收信号的一种方式则是通过雷达天线。雷达天线的基本作用是实现电磁波的自由空间传播的导波传播之间的转换。发射期间天线的特定功能是在将传输过程中的辐射能量集中到具有某种形状的定向波束中,指导光束照亮一个理想方向的目标。在接收期间天线的能量收集包含在反映目标的回波信号并将之传送到接收器。因此,在以发射方式和接收方式工作时,雷达天线是用来实现互易的,但相关的作用是在发送和接收模式中实现的。在这两种模式或角色中,其主要目的是准确地确定的确定目标的方向角。为实现此目的,需要有高度的定向指令(狭义)波束,从而不仅实现所需角精度的同时能够分辨相互考的很近的目标。雷达天线的这一重要功能不仅可以定量的用波束宽度来表示,也可以表示为发射增益和有效接收孔径。后两个参数相互之间成正比,并且与检测距离和角精度有直接的关系,许多雷达都设计成工作在微薄频率,这时适当物理尺寸的天线就能获得窄的波束宽度。上述雷达天线的功能描述意味着一个单一的天线,既用于发射又用于接收。虽然大多数雷达系统都是这样工作的,但是也有例外:有一些单基地雷达使用不同的天线实现接收和发射信号的功能;当然,双基地雷达根据定义,必须有单独的发送和接收天线。由于雷达天线一般具有定向波束,大范围的角度覆盖要求窄波束快速的往复在空域内扫描,以保证不论目标在哪个方向上都能探测到。这就是警戒雷丹和搜索雷达的功能。有些雷达系统设计成一旦探测到目标便可进行跟踪,这种跟踪功能要求专门设计与警戒雷达天线不同的天线。在某些雷达系统中,特别是机载雷达中,将天线设计成既有搜索又有跟踪的功能。雷达天线可分为两大类,光学天线与阵列天线。顾名思义,光学天线是基 黄河科技学院毕业设计(文献翻译) 第 12 页于天线的光学原理的,它包括两个子类,即反射面天线和透镜天线。反射面天线仍广泛用于雷达中,而透镜天线,虽然仍在一些通信和电子战(对抗)的中应用,但是已经不再用于现代雷达系统中。天线罩天线罩是当有必要时用来保护天线在不利的环境条件中不受影响。理想的说,按照要求,天线罩应是完全透过来自(或到达)天线射频辐射以及能够承受环境影响,如风,雨,冰雹,雪,冰,沙,盐雾,闪电,和(在空载高速应用场合时的)热,侵蚀,和其他空气动力学的影响。在实践中,这些环境因素决定了机械设计的天线罩的性能,理想射频透明度必须不受到损害,对 RF透明的要求必须折中考虑,因为机械和电气要求往往是冲突的。天线罩对天线的电性能主要有四方面的影响。光束偏转是电轴的漂移,这对跟踪雷达是关键的。传输损耗是衡量能量被反射和吸收得量度。反射功率在小天线罩中引起天线失配,在打天线罩中引起副瓣。二次效应作用包括去极化和天线噪声增加。天线罩的设计是一项专业技术,和许多书籍都致力于其复杂的细节研究。这部分不是试图提供天线罩设计信息,但相反的目的是使雷达系统设计师弄懂通常隐藏在为各种应用场合提供的各种天线罩后面的天线罩的基本概念。这些是主要类别的雷达天线罩:陆基或舰载系统的天线罩以及机载或弹载的天线罩。虽然两者有显著不同的尺寸和形状,但他们有一些共同的一般特征。天线罩的种类和一般考虑。这些比较感兴趣的雷达天线罩一般有三类:馈源罩,这往往要耐压力,耐高电压,耐加热;附属于反射面的天线罩,能以一个固定的方式改变方向图;和外部天线罩,天线在其中移动。外部天线罩是最常见的并且将做重点介绍。在每一类中,各种蒙皮和蒙皮支撑功能设计可使电气性能受各种环境的影响最小。天线罩的蒙皮可能是刚性的,由框架支撑,也可以是充气支撑的。最常见的刚性罩壁结构被称为均匀的单层,A-夹层,B-夹层,C-夹层,多层夹层和内含金属的介质层。单层。很多天线罩应用中都使用均匀单层天线罩。此类天线罩的材料是玻 黄河科技学院毕业设计(文献翻译) 第 13 页璃纤维增叩陶瓷人造橡胶和整体式泡沫塑料。对于适当的入射角,单层的最佳厚度是介质材料中半波长的整数倍,但许多单层罩只是一个薄壁,接近零厚度。A-夹层。 A-夹层常用的罩壁截面由两层密度较高的薄蒙皮和一层较厚但密度较低的夹心构成。这种结构强度一质量比高。蒙皮通常是玻璃纤维增强型塑料,夹心是泡沫或蜂窝状。为了适合高温应用,已经研制出无机的蒙皮和夹心层。通常,夹层的蒙皮对称或具有等厚度,以使频带中心频率的反射对消。B-夹层。与 A-夹层不同, B-夹层是蒙皮的介电常数低于夹心材料的三层结构。它的壁截面比 A-夹层的重,因为夹心的密度较大。 B-夹层不常用,因为对于好的匹配,夹心层的介电常数太高。c-夹层。 c-夹层是一种五层设计,由两个外蒙皮、中心蒙皮和两个中间夹心层构成。对称的 c-夹层可看做两个背对背的 A-夹层。当 A-夹层没有足够的强度或者无法满足某些电气性能指标时,采用这种结构。需要一层用做暖气道防冰时,也采用这种结构。多夹层。要求强度高、电气性能好、质量轻时,采用具有 7 , 9 、 11 或更多层的多层夹层。有些这样的设计采用玻璃纤维薄板和低密度夹心薄层,可在很宽的频率范围获得好的传输性能。内含金属的介质层。内含金属的介质层用来实现频率滤波、宽频带特性,或者降低天线罩厚度。内含金属薄层显示出有并联在传输线上的集总电路单元的传输线特性。例如,平行金属线栅格具有并联感性导纳传输线的性质。还有许多关于天线罩设计的其他问题、特殊应用考虑和设计因素,但是这些已经超出了本章的讨论范畴,就不再赘述
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