2MHz窄带晶体滤波器的研制

介绍中心频率2MHz,3dB带宽180～200Hz,通常波动小于0.5dB,阻带衰减大于70dB,矩形系数B_(60)/B_3<2,插入损耗小于3dB,输入、输出阻抗均为75Ω,体积为长81mm×宽31mm×高29mm的晶体滤波器的研制.该晶体滤波器的技术指标达到日本MWS-672型抖晃校准仪上用的同种晶体滤波器的技术指标.     

75MHz高衰减小矩形系数晶体滤波器的设计制作

介绍中心频率75MHz、6dB带宽9～10kHz,通带波动小于idB、阻带衰减大于65dB、矩形系数B40/B6<2、插入损耗小于6dB、输入输出阻抗均为50Ω、体积为42mm×20mm×18mm的晶体滤波器的设计制作。该晶体滤波器用综合法设计,采用三节六晶体窄带差接桥式带通晶体滤波器的电路结构,用比高频滤波器效果更好的电容分压的方法进行阻抗变换,不用常用的差接变量器进行阻抗变换。该晶体滤波器的技术指标优于用户提出的技术指标,接近北京无线电仪器二厂1986年引进的西德R/S公司生产的ESH3型电磁干扰测试接收机上所用同种晶体滤波器的技术指标。整机用后认为该滤波器性能良好,满足了整机的设计要求,样机于1989年12月通过设计定型鉴定。     

宽带石英晶体滤波器

一、引言宽带石英晶体滤波器的相对带宽超过1％。为了实现这样宽的通带,就必须在晶体滤波器电路中加展宽线圈。展宽线圈电感是组成宽带石英晶体滤波器的重要部分。使用基频晶体的宽带滤波电路,大都在电路中加并联展宽线圈,而使用泛音晶体的宽带滤波电路,大都在电路中加串联展宽线圈。本文介绍我们研制的中心频率2.4MHz、3dB带宽70kHz宽带通石英晶体滤波器。在火箭,     

全通型带阻晶体滤波器的设计和制造

叙述了500kHz全通型带阻晶体滤波器的设计原理,电路元件值的计算公式。通过实例描述了设计过程和调试方法。     

低频晶体滤波器的设计

主要介绍以19.2kHz为例的低频晶体滤波器设计制造的全过程及如何减小低频晶体滤波器的体积。选用衰减特性比较陡的对称两节差接桥式晶体滤波器电路,保证了19.2kHz低频晶体滤波器矩形系数小。     

短期频率稳定度自动测量装置

本文介绍了授率稳定度的表征,研制的一台频率短期稳定度测量装置和一个测时精度为0.1ns的时间间隔计数器,它可实现短稳时域阿伦方差无间隙采样。通过IEEE—488接口总线实现了对频综的多点连续和对振荡器的跟踪自动测量。本装置频率稳定度测量范围为0.2～500MHz,(并可扩展到10GHZ)。自校准σ_y(τ)=5E一6/τ.S_φ(0.1Hz)=-135dB/Hz,S_φ(1Hz)=—138dB/Hz,S_φ(10Hz)=-140dB/Hz,S_φ(100Hz)=-150dB/Hz。本装置经多次实测实验,性能可靠,测量数据可信。     

5.5—12兆赫单片晶体滤波器设计

本文介绍5.5—12MHz单片晶体滤波器的工作原理、设计方法及改善阻带特性的方法。采用这种设计所制作的滤波器,在5.5—7MHz频段内最大阻带衰减为60db,矩形系数B_(40)/B_3=4。在8—12MHz频段内,最大阻带衰减为70db,矩形系数B_(40)/B_3=2.6。这两种滤波器都封装在J_1金属壳内,外形尺寸为22×12×22mm。因此它具有体积小,温度稳定性好,机械稳定性好,造价低廉等优点,适合于无线电设备集成化的需要。     

用于数字用户传输系统的定时槽路机械滤波器

本文阐述定时槽路机械滤波器的设计方法和实验结果。复合纵模变换器通过附加一层恒系数合金片至压电陶瓷片的每一个电极表面而被做成夹层结构。对变换器的等效电路常数和三次纵模引起的寄生响应的抑制作了分析。实验滤波器的尺寸是:20L×12W×5Hmm,它与14脚双列直插式集成电路的尺寸相同。滤波器的中心频率为200KHz,其插入损耗低达0.5～0.7dB,而3dB带宽为2.1～2.4KHz。在中心频率下输入输出的相位差约为40°,相位线性度非常好,其相位斜率低达0.07～0.08/Hz。在0～1.5MHz频率范围内衰减频带为30dB或更大,改善了设备的信噪比。滤波器的输入/输出阻抗在8.5～8.9KΩ之间,它与CMOS电路的阻抗匹配是满意的。温度特性表明,在5～60℃之间插入损耗的变化为0.6dB,而相位变化为11°。     

3GHz低噪声倍频器的结构设计

一、引言 3GHz低噪声倍频器主要用于三座标雷达发射和接收系统捷变频率合成器中。它具有极好的短期频率稳定度及频谱纯度。文中着重介绍了倍频器结构的设计方案。在设计中采用了微带技术,封闭式隔离屏蔽及三板线传输带型式,经测试获得了较好效果。实验结果达到;短期频率稳定度σ_y(τ)优于1.7×10~(-10)/ms;5.5×10~(-11)/10ms;￡(f):—105dB/Hz(1kHz);-115dBc/Hz(10kHz)。杂波抑制度大于60dB。上述指标相当于或超过美国HP8672频率综合器中倍频器的技术水平。     

甚低噪声FET输入放大器

本文介绍了一种甚低噪声 FET 共源一共栅输入放大器的设计、原理和特性。这种放大器在频率为500Hz～500kHz 范围内的噪声指标小于1.2nV/Hz~(1/2)和0.25fA/Hz~(1/2)。适当加以变化,可用千1Hz～30MHz 频率范围的各种要求低噪声增益的场合。     

Learning in an immersive digital theater

The Houston Museum of Natural Science, in collaboration with Rice University has an outreach program taking portable digital theaters to schools and community sites for over five years and has conducted research on student learning in this immersive environment. By using an external independent evaluator, the effectiveness of NASA-funded Education and Public Outreach (EPO) projects can be assessed. This paper documents interactive techniques and learning strategies in full-dome digital theaters. The presentation is divided into Evaluation Strategies and Results and Interactivity Strategies and Results. All learners from grades 3–12 showed statistically significant short-term increase in knowledge of basic Earth science concepts after a single 22-min show. Improvements were more significant on items that were taught using more than one modality of instruction: hearing, seeing, discussion, and immersion. Thus immersive theater can be an effective as well as engaging teaching method for Earth and Space science concepts, particularly those that are intrinsically three-dimensional and thus most effectively taught in an immersive environment. The portable system allows taking the educational experience to rural and tribal sites where the underserved students could not afford the time or expense to travel to museums.     

Stochastic particle acceleration by the forced interaction of relativistic current sheets

We address the problem of interacting relativistic current sheets in self-consistent kinetic plasma simulations within the framework of the Particle-In-Cell model. The interaction is enforced in head-on collisions of up to 10 current sheets at relativistic bulk speeds. The simulations are motivated by the general problem of Poynting flux dissipation in ‘striped wind’ configurations presumably governing the relativistic outflows pervasive in pulsar winds and gamma-ray bursts. We identify the generation of non-thermal particles and formation of a stable power-law shape in the particle energy distributions f(γ) dγ ∝ γ^−s dγ. In 1D, a spectral index s ∼ 2 is observed and attributed to a stochastic Fermi-type acceleration mechanism. In 2D, the generic index of s ∼ 3–4 is retained as in previous simulations of individual current sheets. Whereas in 2D the high energy cut-off is constrained by the limited dissipation of magnetic energy, in 1D the process converts the bulk motion of current sheets towards directed particle momentum of an exclusive class of non-thermal particles.     

Concept options for the aerial survey of Titan

Various aerial platforms intended for long endurance survey of the Titan surface are presented. A few novel concepts are introduced, including a heated methane balloon and a balloon with a tethered wind turbine. All the concept options are predicted to have lower scientific payload fractions than the Huygens probe. It is concluded that the selection of the best aerial platform option depends on more accurate mass estimates and a clear decision on whether, or not, in situ surface composition measurements are required in conjunction with aerial remote sensing.     

Heterogeneous solid/gas chemistry of organic compounds related to comets,meteorites, Titan,and Mars: Laboratory and in lower Earth orbit experiments

To understand the evolution of organic molecules involved in extraterrestrial environments and with exobiological implications, many experimental programs in the laboratory are devoted to photochemical studies in the gaseous phase as well as in the solid state. The validity of such studies and their applications to extraterrestrial environments can be questioned as long as experiments conducted in space conditions, with the full solar spectrum, especially in the short wavelength domain, have not been implemented. The experiments that are described here will be carried out on a FOTON capsule, using the BIOPAN facility, and on the International Space Station, using the EXPOSE facility. Vented and sealed exposition cells will be used, which will allow us to study the chemical evolution in the gaseous phase as well as heterogeneous processes, such as the degradation of solid compounds and the release of gaseous fragments.     

基于LuGre模型的电液加载系统摩擦补偿

为了提高电液加载系统控制精度,针对摩擦问题提出了基于LuGre摩擦模型的前馈补偿方法.建立了用于摩擦仿真分析和补偿器设计的电液加载系统数学模型;通过实验获取并分析了相关的摩擦数据;基于实验数据进行LuGre模型参数辨识,把LuGre模型和辨识结果引入电液加载系统数学模型,并进行仿真结果与实际摩擦数据的对照,证明了LuGre摩擦模型的准确性.设计前馈补偿器,进行了实验对比,实验结果表明前馈补偿器可将摩擦产生的控制误差有效地降至未补偿时的30%左右.      

CoRoT and Kepler results: Solar-like oscillators

The space-borne observatories CoRoT (Convection Rotation and planetary Transits) and Kepler have provided photometric time series data of unprecedented precision for large numbers of stars. These data have revolutionized the fields of transiting exoplanets and asteroseismology. In this review some important asteroseismic results obtained using data from the CoRoT and Kepler space missions concerning stars that show solar-like oscillations are discussed. These results comprise, among others, measurements of the location of the base of the convection zone and helium second-ionization zone in main-sequence stars, the presence (or not) of core-helium burning in red-giant stars, as well as differential rotation in these stars.     

The ESA scientific programme

The ESA scientific programme has, so far, provided several significant astrophysics experiments and further important missions are scheduled for execution during the next decade. These missions are briefly summarised together with several astrophysics investigations presently under study.     

HELIO: The Heliophysics Integrated Observatory

Heliophysics is a new research field that explores the Sun–Solar System Connection; it requires the joint exploitation of solar, heliospheric, magnetospheric and ionospheric observations.     

Radioactivity of the Moon and planets

In this report the main results of the study of radioactivity of the solar sistem bodies are considered. The radioactivity of the Moon and planets was measured by means of vehicles in situ. The radioactivity of the lunar samples, brought to the Earth was studied with laboratory equipment.     

应用于毫米波反射计的多项式校准方法

为了在毫米波波段准确测量波导器件的反射系数,提出了一种应用在反射系数测试前端(反射计)中的校准方法.该校准方法采用基于多项式的误差模型,使得每一个误差项的求解都转化成一个求解轨迹圆圆心的问题,同时不影响求解精度.采用一个滑动负载、一个滑动短路和一个短路器,在毫米波波段降低了对标准件理想程度的要求.实验中搭建了一个Ka波段的反射计,图解误差项的求解过程,分析了误差项的物理意义.把校准后的测量结果与商用矢量网络分析仪(VNA,Vector Network Analyzer)进行比较,吻合较好.同样比较了一组W波段反射计对波纹喇叭的测量结果,进一步验证了方法的合理性.