共查询到20条相似文献,搜索用时 31 毫秒
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If modern airborne radar systems are to function properly, the radar antenna radiation patterns must meet certain specifications. Until recently, most radar antennas were designed and tested in a clean antenna environment, i.e., there is no near field scattering from host structures or radome effects. However, these higher order effects are the matter of increasing concern with added performance demands in the ever-increasing jammer and clutter interference environments. We investigated the capabilities and limitations of currently available analysis techniques and computer codes for installed performance of airborne radar antenna systems. Then we developed an extended ray-optical technique that could predict total installed performance of airborne radar antenna systems, i.e., the near field scattering from aircraft structures and radome effects. The new analysis technique utilized a ray-tracing method in both airframe and radome simulation. Thus, it can efficiently predict the total installed performance of large radar antenna systems on an aircraft structure 相似文献
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Nowadays, more and more attentions are paid to electromagnetic incremental forming(EMIF), especially for a part with a large-scale size, e.g., an integral panel with stiffened ribs. In this work, the bending of a panel into a double-curvature profile via EMIF is carried out experimentally and evaluated by comparing the formed profile with the desired profile. During the process,discharges at four positions along different discharge paths are designed. The effects of forming parameters on the die-fittingness of the workpiece are discussed, for which two evaluation indices are used to judge forming results. The results show that a discharge voltage in an incremental mode is helpful to improve the fittingness and avoid the collision rebound against the die at the same time.Discharging at the diagonal positions with the ‘‘X" discharge path exhibits the minimal shape deviation and the best forming uniformity. On the contrary, discharging at the parallel positions with the ‘‘Z" discharge path obtains the worst forming quality. Overlap of the coil at different positions should be given during EMIF; however, a lower overlap rate of the coil helps improve the forming quality. The results obtained in this work are useful for forming integral panels with stiffened ribs via the EMIF process. 相似文献
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研究了射频感性耦和等离子体(ICP)中悬浮电位在模式转化过程(E-H模式)的变化多样性。实验研究了射频功率在5W-1000W,气压在2Pa-50Pa的范围内,通过改变导电地面积、匹配网络、气压等参数,使用Z-Scan系统、电流电压探头以及静电探针进行测量的等离子体悬浮电位在模式转化过程中随功率变化的多种形式,同时给出了r型射频匹配网络的正负反馈区的区别,并对产生的多种现象进行了的理论解释。 相似文献
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An optimization problem of an antenna coverage pattern for a regional communications satellite when an antenna-pointing error exists is discussed. A new performance measure is introduced to evaluate the coverage pattern. This measure is defined as the statistical mean of the ratio between two areas, the full service area and the part of it covered by the antenna. The optimum coverage pattern which maximizes this measure under certain constraint is obtained. The results of numerical calculations are included to demonstrate the technique. 相似文献
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Pulse chasing is a technique implemented by a bistatic or multistatic radar system that allows rapid and efficient search of a desired volume of space whereby the receiving antenna is made to follow or “chase” the transmitted pulse as it travels radially outward from the transmitter antenna. An expression for receiver antenna scan rate requirements is derived that corrects an error in the prior literature. The results give significantly reduced scan rates in the forward scatter region near the baseline showing that pulse chasing is more easily implemented using conventional analog beamformer phased array technology than was suggested by prior work 相似文献
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D. A. Gurnett A. M. Persoon R. F. Randall D. L. Odem S. L. Remington T. F. Averkamp M. M. Debower G. B. Hospodarsky R. L. Huff D. L. Kirchner M. A. Mitchell B. T. Pham J. R. Phillips W. J. Schintler P. Sheyko D. R. Tomash 《Space Science Reviews》1995,71(1-4):597-622
The Plasma Wave Instrument on the Polar spacecraft is designed to provide measurements of plasma waves in the Earth's polar regions over the frequency range from 0.1 Hz to 800 kHz. Three orthogonal electric dipole antennas are used to detect electric fields, two in the spin plane and one aligned along the spacecraft spin axis. A magnetic loop antenna and a triaxial magnetic search coil antenna are used to detect magnetic fields. Signals from these antennas are processed by five receiver systems: a wideband receiver, a high-frequency waveform receiver, a low-frequency waveform receiver, two multichannel analyzers; and a pair of sweep frequency receivers. Compared to previous plasma wave instruments, the Polar plasma wave instrument has several new capabilities. These include (1) an expanded frequency range to improve coverage of both low- and high-frequency wave phenomena, (2) the ability to simultaneously capture signals from six orthogonal electric and magnetic field sensors, and (3) a digital wideband receiver with up to 8-bit resolution and sample rates as high as 249k samples s–1. 相似文献
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Waters William M. Eikenberg Andrew F. 《IEEE transactions on aerospace and electronic systems》1968,(6):886-892
This paper describes the design, construction, and performance of an experimental radar, in which an electronically scanned X-band array is employed as the receiving antenna. Backscatter from targets uniformly illuminated from a separate transmitting antenna is intercepted by 128 horn antennas, unequally spaced over a nine-foot circular aperture. The received signals are processed electronically to provide a complete scan of a 30X30 degree field every ten milliseconds. Resulting target images were displayed on a cathode ray tube and recorded on 16-mm motion picture film, for varying conditions of target motion using monochromatic and frequency-modulated X-band illumination. Sequences of motion picture frames obtained from a rotating copper cone are presented, which demonstrate significant changes in the image and side-lobe interference patterns for small changes in target aspect angle. Side-lobe interference effects were reduced by integrating many antenna scans as the target rotated; a clear image of a foil letter R is presented that demonstrated this result. The main objective of this work was to test this radar technique as an approach to target recognition. 相似文献
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针对国内外高温励磁绕组存在的缺陷与不足,提出了一种新型的迷宫形励磁绕组结构,首先通过电火花线切割制造出单层迷宫形线圈,并在线圈匝间和层间充分均匀地填充耐高温绝缘材料;然后通过真空钎焊工艺实现多层迷宫形线圈的牢固焊接,最后将焊接成型的多层线圈封装成迷宫形绕组,并应用于单自由度高温磁悬浮轴承试验台中,实现了550℃被悬浮物体近20h的稳定悬浮.研究结果表明:线圈焊缝的高温电阻值小,抗剪切强度满足要求,焊缝的金相组织致密均匀;绕组匝间和层间绝缘性能良好;迷宫形励磁绕组在原理和工艺上是可行的.对高温悬浮试验后的迷宫形绕组内部形貌进行观察后发现封装线圈的高温绝缘材料存在一定的缺陷,有待进一步研究. 相似文献
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为了分析射频离子推力器热特性,建立了射频离子推力器整体热模型,基于二维流体模型,对11cm射频离子推力器开展了放电室等离子体仿真,获得了电子温度、电势分布等关键参数;以等离子体仿真结果和实测束电流为输入,获得了各热源的热通量;通过有限元计算获得了关键部组件的温度分布,与实验结果进行了对比分析。研究结果显示:放电室内电子温度约为3.6eV~3.9eV,等离子体电势最高20V,发热损耗主要来自带电粒子轰击放电室壁面和栅极造成的能量沉积、激发原子的热辐射以及射频线圈自身的发热损耗,温度仿真与实测结果一致性良好,最大误差7%,仿真得到的温度分布可以作为输入参数进一步研究栅极受热形变及对束流的影响。 相似文献
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The author presents a new technique of steering an array antenna by introducing time-varying phase weights. It is shown that the technique is equivalent to placing a linear phase and linear frequency offset across the array when transmitting a linear frequency modulated (LFM) waveform. The technique reduces array dispersion and increases the operating bandwidth. An element level signal generator is presented as a possible way of implementing the time-varying weights. A possible array implementation is also shown.<> 相似文献
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拖曳天线力学特征和控制是飞机对潜通信系统进一步深入论证需要解决的关键问题之一,而对其稳态动力学研究是进行拖曳天线力学特征和控制的基础。文章通过对其运动状态及其受力进行分析,建立机载甚低频拖曳天线稳态动力学模型。运用打靶法进行求解,计算出了在不同空气阻尼情况下天线稳定构型,分析了绳索的张力分布情况并比较了空气阻尼对天线稳... 相似文献
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Mavroides William G. Dennett Lancer G. Dorr Leon S. 《IEEE transactions on aerospace and electronic systems》1966,(3):323-331
A height-finding technique utilizing the relative phase between a series of point sources of a traveling-wave array is described. The point sources in the focal region of a torus antenna are used to control the phase of the antenna elevation pattern in space. Signals received from a given beam angle will arrive at each terminal of the traveling-wave feed with a different phase. By comparing this phase with a reference phase, the angular direction of an arriving plane wave can be measured with considerable accuracy. Thus a radar system with a single antenna and feed structure can be employed to yield instantaneous height coverage along with the usual range data. 相似文献
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The described method of antenna null steering makes use of calibrated and stored weight distributions for each solid angle increment of a radar search volume. Based upon direction measurement to an interference source, the appropriate weight distributions are calculated for each relative antenna position. In addition to the programmed part an adaptive inner loop is included for fine null adjustment. The major parameters and characteristics of the null steering technique are studied and evaluated through computer simulation programs. 相似文献
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N. D. Akhmetov M. M. Gimadeev V. N. Drulis V. A. Krivosheev T. V. Rzaeva 《Russian Aeronautics (Iz VUZ)》2011,54(1):108-113
A technique for calculating the energy parameters of shock waves at electrical discharge in water is presented for the transition
region of discharge channel expansion using as the base the predetermined characteristics of discharge circuit. The technique
is based on the solution of energy transport equation that is similar in form to that of radiative transfer. The validity
of the presented approach was experimentally verified. 相似文献
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A direction-finding technique is presented that is capable of simultaneously estimating the arrival angles of multiple signals. Pulsed as well as continuous signals can be handled with the signal form only approximately specified. An adaptive antenna array is used as a processing device in the estimation technique. The effect of input signal and feedback loop parameters upon estimate bias is discussed. 相似文献
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The technique of adaptive filtering as applied to the design of a frequency-reuse receiving antenna which can provide optimum isolation from signals of unwanted polarization. 相似文献