非谐振单元加载的宽带超表面透镜天线设计

传统标准增益喇叭天线测试系统在测试物体的电磁特性时,由于要满足入射波为平面波的要求,通常要满足天线的远场条件,这样在测试过程中会产生绕射等现象,影响测试结果.通过在天线波导口处加载相位补偿的非谐振超表面单元可以改变电磁波的传播方向,使其在近场处也可以产生近似平面波的效果,可解决在测试过程中绕射等现象导致的测试结果不准确...     

任意角入射到非均匀等离子体的WKB法

用WKB法研究了以任意角入射的电磁波在非均匀非磁化等离子体中的衰减特性,给出了电磁波在非均匀非磁化等离子体中的双程衰减公式。选用抛物线型等离子体密度分布进行计算,基于等离子体共振吸收概念分析了双程衰减与入射电磁波频率、等离子体碰撞频率、等离子体最大密度和电磁波入射角等的关系。对等离子体隐身研究有一定的参考价值。     

A directed search for extraterrestrial laser signals

This paper analyzes the technical feasibility of interstellar communication at infrared frequencies, both in its own right and in comparison with communication at radio frequencies. The analysis considers both the practical and fundamental limits affecting communication over interstellar distances and concludes that for specified transmitter and receiver locations communications at infrared and radio frequencies can be equally effective. On this basis a search for extraterrestrial signals at infrared wavelengths is equally as valid as any planned microwave effort. Work is now in progress to adapt a 10 micrometers heterodyne spectrometer to search for CO2 laser signals from 200 nearby stars.     

Eigen Ultra-Low-Frequency Magnetosonic Oscillations of the Near Plasma Sheet

A critical analysis of existing theories of the magnetospheric resonator for fast magnetosonic waves is performed. A new variant of the theory is suggested, according to which the near-Earth part of the plasma sheet plays the role of the resonator. It is shown that the magnetosonic wave is locked inside this region over its entire boundaries. The eigen frequencies of resonator modes are in a good agreement with observed values (0.8, 1.3, 1.9, 2.6, 3.4, ... MHz), both when estimated in the order of magnitude and when calculated exactly in the context of a simple model.     

碰撞等离子体的宽频带电磁波吸收特性

针对具有金属反射面的非均匀等离子体对电磁波的反射、吸收问题,采用求解波动方程的方法构造相应的边界条件,详细研究各种参数等离子体对电磁波的吸收特性,讨论对等离子体参数及波动方程进行归一化的方法,得到归一化条件下的等离子体宽频带吸收特性。计算分析表明,对于电子密度为某种渐进分布的有碰撞的低温等离子体,当碰撞频率与最大电子密度处的等离子体频率相近或略大,且等离子体层的厚度足够大时,在一个较宽的频带内,等离子体对电磁波有较强的吸收作用。研究结论可以用于等离子体参数的选择,及等离子体隐身的参数设计。     

一种多通道高隔离度毫米波发射组件的设计

随着雷达技术的发展,毫米波单片集成电路技术日趋成熟,小型化、轻量化、多功能的毫米波雷达在国内外得到了深入的研究和应用。为满足毫米波雷达的需求,设计了一种多通道高隔离度毫米波发射组件。采用普通FR4多层板实现电源和控制信号走线,其中功分器芯片、电容、电阻等器件装配在FR4多层板的表层;采用低损耗的Rogers 5880微波板材进行毫米波射频传输。为提高通道间和级联功放间的隔离度,进行金属隔墙处理,以获得更好的物理隔离。通过对腔体进行电磁仿真,使腔体的谐振频率高于工作频带。该组件质量仅为41 g,输出功率不低于35.5 dBm,发射效率大于16%,可应用于毫米波SAR和固态发射机等场景。     

遥测信号差分解调仿真

非相干解调由于不需要产生同频同相的本地载波,避免了因为本地载波的不精确导致的解调信号失真,降低了在实际系统中接收端实现的复杂度。文章分析了遥测信号的一种非相干解调的算法,并进行了仿真,得出高斯白噪声（AWGN）信道中的误码曲线。     

Comparison of the effects induced by the ordinary (O-mode) and extraordinary (X-mode) polarized powerful HF radio waves in the high-latitude ionospheric <Emphasis Type="Italic">F</Emphasis> region

Using the results of coordinated experiments on the modification of the high-latitude ionosphere by powerful HF radio emission of the EISCAT/Heating facility, effects of the impact of powerful HF radio waves of the ordinary (O-mode) and extraordinary (Х-mode) polarization on the high-latitude ionospheric F region have been compared. During the experiments, a powerful HF radio wave was emitted in the magnetic zenith direction at frequencies within the 4.5–7.9 MHz range. The effective power of the emission was 150–650 MW. The behavior and characteristics of small-scale artificial ionospheric irregularities (SAIIs) during O- and X-heating at low and high frequencies are considered in detail. A principal difference has been found in the development of the Langmuir and ion–acoustic turbulence (intensified by the heating of the plasma and ion–acoustic lines in the spectrum of the EISCAT radar of incoherent scatter of radio waves) in the О- and Х-heating cycles after switching on the heating facility. It has been shown that, under the influence on the ionospheric plasma of a powerful HF radio wave of the Х-polarization, intense spectral components in the spectrum of the narrow-band artificial ionospheric radio emission (ARI) were registered at distances on the order of 1200 km from the heating facility.     

Synchronized SETI-the case for "opposition"

If the signals being sought in search for extraterrestrial intelligence (SETI) programs exist but are brief (for example, they are produced intermittently to conserve energy), then it is essential to know when these signals will arrive at the Earth. Different types of transmitter/receiver synchronization schemes are possible, which vary in the relative amount of effort required by the transmitter and the receiver. The case is made for a scheme that is extremely simple for the receiver: Make observations of a target when it is at maximum angular distance from the Sun (i.e., "opposition"). This strategy requires that the transmitter has accurate knowledge of the distance and proper motion of the Sun and the orbit of the Earth. It is anticipated that within the next 10-20 years it will be possible to detect directly nearby extrasolar planets of approximately terrestrial mass. Since extraterrestrial transmitters are expected to have significantly more advanced technology, it is not unreasonable to expect that they would be able to detect the presence of the Earth and measure its orbit at even greater distances. This strategy is simple to implement, and opposition is also typically the time when observations are easiest to make. Limited opposition surveys contained in a number of all-sky surveys have already been performed. However, full-sky opposition surveys are best suited to detectors with very large fields of view.     

The Role of Wave–Particle Interactions in the Dynamics of Plasma in the Polar Cusp

This paper presents a review of observations of low-frequency plasma waves together with plasma particles performed by Interball 1 and its subsatellite Magion 4 and by the Freja satellite in different cusp regions. The detailed study of the wave spectra together with the electron distribution functions indicates the correlation between the presence of lower-hybrid waves and of particles with energies higher than in the surrounding space. These experimental facts suggest that strong coupling between waves and particles is responsible for plasma heating. The Freja data with a high time resolution allow identification of the process of energy transport via a cascade from low frequency waves to high frequency waves accompanied by electron energization.     

Features of wave excitation of the electrostatic ion cyclotron type in the auroral ionosphere

Broadband electrostatic noise in the auroral ionosphere can be identified as a version of waves of an electrostatic ion cyclotron type, excited by plasma instability resulting from an inhomogeneous distribution of wave energy density. Broadband waves are generated due to both electric field inhomogeneities and plasma density inhomogeneities. The effect of the form of the distribution of electric field and plasma density inhomogeneities on the excitation of instabilities is studied. Also there is shown the role of the characteristic scale of inhomogeneities in the generation of electrostatic ion cyclotron waves due to the development of instability of this kind. The study of these issues, which are important for understanding the processes in the auroral region, is the subject of this paper. The work presents also a comparison of numerical results obtained using both satellite data and model approximations.     

星间链路发射机时延零值的数字标定算法

The traditional absolute calibration based on oscilloscopic observation is not suitable for crosslink transmitter. A new calibration algorithm is developed by using a digital signal processing technique. The output signal of crosslink transmitter and the pulse per second signal are sampled in synchronization. At first, the delay reference is determined according to straight line fitting for the signal level stepping segment. The sampling data of crosslink transmitting signal is decimated and then phase acquisition processing is made to determine the initial synchronization point. A fine search for the start of the pseudo random code has been processed between front and rear of the initial synchronization point. Finally, the transmitter delay can be obtained according to the sampling frequency and the calibration delay of the test cable and attenuator. Compared with the oscilloscopic observation method, the analysis and test results show that the proposed technique has overcome the faults caused by whole chip ambiguity and the calibration accuracy can be improved by an order of magnitude.     

基于发射站触发脉冲延时的双站时间同步模型

提出了一种双基地雷达的时间同步方法模型。基于距离跟踪与处理,通过调整发射站发射机触发脉冲的延迟时间,可保证接收站在单站和双站工作时目标信号都能重合。仿真结果表明:该模型正确。     

基于最佳检测的雷达发射-接收极化联合优化方法

基于最佳检测准则,提出了一种新的雷达发射-接收极化联合优化方法。首先,建立了全极化雷达目标回波模型,设计了基于纽曼-皮尔逊(Neyman-Pearson)准则的雷达目标全极化检测算法,推导分析了检测性能;其次,提出了雷达发射-接收极化的联合优化方法,提高了雷达目标的检测性能;最后,仿真试验结果表明,本算法能够显著提高雷达目标的检测性能。     

Recent experiments in laser supported absorption waves

Recent experimental studies with laser supported absorption waves, arising from intense laser radiation incident upon various surface materials, are discussed. The propagation characteristics of both subsonic (laser supported combustion), intensity about 10⁵ W/cm², and supersonic (laser supported detonation), intensity greater than 10⁶ W/cm², waves are described, including the dependence of wave speed on laser intensity, beam diameter, gas density and laser wave length. Measurements of the plasma properties in such waves are described, and the analysis of these data allows conclusions identifying the dominant transport mechanism in such waves. It is also concluded that in the LSC (subsonic) case, radial flow ahead of and within the wave are dominant features of the wave structure. The equipment and laser facilities used in the experiments are also discussed.     

框架结构模态分析的行波方法

基于空间框架结构的行波动力学模型，给出获取结构模态参数的一个新方法，将由一维波导组装成的框架结构的振动作为弹性波研究。弹性波在波导上传播，在结点处反射和散射。结构的模态特性在结构呈自由振动状态时得以体现，据此建立一个关于结构内行波的特征值总理问题，并由此求得结构的固有频率及振型。文中还给出了与有限元方法结果的比较。     

降低电磁波在再入等离子体中衰减的仿真分析

对电磁波在再入等离子体中的衰减特性进行了分析。在不减少辐射口面处等离子体电 子总数的条件下,提出一种极化方向电子密度周期变化分布降低电磁波衰减的方法。对于电 子密度均匀分布与再入过程中实际分布的等离子体模型,采用发射与接收天线,对电磁波在 等离子体中的传播特性进行仿真。得到了电子密度均匀分布与周期变化时的电场分布图,分 别计算了电子密度均匀分布与实际分布时的电磁波衰减,对原分布与周期变化分布时产生的 电磁波衰减进行比较。仿真结果表明,极化方向电子密度的周期变化,可有效改善电磁波的 传播特性,使电磁波衰减降低。
     

卫星通信地面终端射频一致性测试及仿真分析

介绍了卫星通信系统体制、地面终端的基带处理过程,以及发射机射频指标和测试算法,利用MATLAB和ADS软件搭建了基带信号生成模块、发射机模块,对终端发射机的发射功率、误差矢量幅度、占用带宽、邻道干扰进行了仿真。仿真结果表明,上变频器的射频带宽过小会使调制信号的误差矢量幅度增大,放大器工作在非线性区会对占用带宽和邻道干扰有较大影响,使发射机不满足射频一致性要求。本文的研究结果对设计卫星通信地面终端具有一定的借鉴意义。     

S波段超小型调频发射机

介绍Ｓ波段超小型调频发动机方案的选择，电路设计，结构安排，并对该发射机的稳定性和质量进行了分析，该发射机已通过机载环境条件试验和地面接收机的对接试验，并已通过鉴定，具有９０年代国外同类产品的水平。     

超声电喷推力器的驻波特性

为研究超声电喷推力器(UAET)驻波尺寸特性的相关变化规律，建立发射极液面的液体振动数值模型，并开展驻波尺寸测量试验对数值模型进行验证。对比驻波间距的测量值与计算值发现，两者在变化趋势上可认为一致，且计算误差在6.55%以内。在此基础上，利用数值模型对不同波源频率、振幅下的驻波相关参数进行计算。实验结果表明，随波源频率升高，驻波间距、高度以及半径均下降，其影响机制在于频率主要对波纹形成时间产生影响；而振幅的升高对间距几乎不产生影响，仅会导致驻波高度和半径升高，其影响机制在于振幅对波纹形成应力产生影响。