Ka波段低温低噪声放大器的设计

介绍了Ka波段低温低噪声放大器的设计和试验结果。在物理温度20K的环境下,在4GHz频率范围内,噪声温度小于27K,增益大于18.5d B。     

带STC控制系统的RF-IF放大器组件的研制

介绍了带STC控制系统的RF-IF放大器组件的研制工作。该组件包含有多个功能单元,有低噪声放大器、镜像抑制混频器、前置中频放大器、STC控制电路、PIN电调衰减器等。介绍了组件整体和各功能单元的设计思路和设计结果。     

一种制冷射频接收前端的研究

概述了制冷射频前端的组成,对其中关键器件真空窗及隔热波导组件、低温低噪声放大器和超导滤波器的设计进行描述。给出了真空窗及隔热波导组件、低温低噪声放大器和超导滤波器主要性能测试实例,制冷射频前端主要指标噪声温度≤10 K,带外抑制≥120 dB。     

深空探测用超导滤波器及滤波放大组件

研制了针对深空探测的超导滤波器和超导滤波放大组件,该超导滤波器在无需后期调谐的情况下,回波损耗大于25.16dB,驻波比小于1.12,插入损耗约0.04dB,阻带抑制达到了115dB以上;超导滤波放大组件的增益为30dB±0.2dB,回波损耗约为20dB;而组件的噪声温度仅为8K~9K。     

X波段接收机低噪声放大器设计

设计了一种采用Ga As p HEMT管芯的小型化宽带超低噪声放大器,利用ADS微波仿真软件进行原理图设计、优化。其中管芯采用单电源加电,避免了双电源输入端隔直电容对噪声的引入;另外,电路结构采用电阻负反馈拓展了带宽,同时也增加了电路的稳定性,实现较好的输入输出匹配特性。设计的低噪放在7GHz—10GHz频率范围内噪声系数小于0.7d B,增益大于30d B,输入输出回波损耗小于-10d B。低噪声放大器的尺寸仅为23mm×18mm×10mm。     

上海光源储存环主支撑减振研究

 上海光源是一台在建的第三代同步辐射光源,对束流轨道稳定性要求很高。由磁铁和支架组成的支撑组件的机械稳定性是影响束流轨道稳定性的重要因素。对主支撑组件样机的测试结果表明,其最低共振频率处放大倍数为50左右,超过要求5倍。因此,需要研究相应的减振措施。利用阻尼减振原理设计了一种约束阻尼结构。在样机上的测试结果表明,安装该装置后,支撑组件的共振放大倍数最大可以降低91.8%,对应的功率谱密度的峰值可以降低25 dB。因此,该装置可以用来增加支撑的稳定性。     

上海光源储存环主支撑减振研究

上海光源是一台在建的第三代同步辐射光源,对束流轨道稳定性要求很高。由磁铁和支架组成的支撑组件的机械稳定性是影响束流轨道稳定性的重要因素。对主支撑组件样机的测试结果表明,其最低共振频率处放大倍数为50左右,超过要求5倍。因此,需要研究相应的减振措施。利用阻尼减振原理设计了一种约束阻尼结构。在样机上的测试结果表明,安装该装置后,支撑组件的共振放大倍数最大可以降低91.8%,对应的功率谱密度的峰值可以降低25 dB。因此,该装置可以用来增加支撑的稳定性。     

X波段高灵敏度超导前端组件

X波段超导前端组件应用于高灵敏度接收机,选频放大微弱信号,抑制发射泄露信号干扰,能够显著提高接收机的灵敏度和抗干扰能力。该组件主要包括三种器件:高温超导滤波器、低温低噪声放大器和低温隔离器。组件在15K温度平台下,主要性能指标为:等效噪声温度小于13K,增益31dB,发射频率抑制度大于110dB,承受阻带连续波功率3W,输入输出驻波比均小于1.25。     

接收平台的低噪声放大器设计

设计了一种用于天文台VLBI天文观测系统的超宽带低噪声放大器,并给出了仿真及测试数据。此低噪放采用了TRIQUINT公司的TGA2525型单片级联结构,为了能够调节增益的大小及平坦度,在单片级间加入了均衡和衰减电路。在2-14GHz频率范围内实现了噪声系数优于3.2d B,增益大于35d B,平坦度小于3.3d B,输入输出回波损耗小于-10d B,1d B功率压缩点输出功率大于17d Bm。     

UHF波段宽阻带高温超导滤波器设计

在分析电容加载的微带线谐振器模型的基础上,提出一种基于叉指电容、块状电容和弓形折线电感的新颖谐振器,其第一谐频位于5.6f_0外。利用该谐振器,在28mm×12mm×0.5mm的YBCO/MgO高温超导基片上设计制作了4节超导滤波器,中心频率为500MHz,相对带宽为1%。测试结果表明该滤波器具有优异性能,带内插损小于0.3d B,反射损耗优于15d B,通带与5.6f_0处寄生通带之间的抑制度大于75d B,实现了宽阻带和高抑制度的带外抑制特性。     

低温低噪声放大器测试平台的结构设计

本文介绍了低温低噪声放大器的应用情况,以及确保它正常工作所需的结构设计方面的一些问题。     

The Coulomb Gas at low temperature and low density

We study the quantum Coulomb Gas ofN particles with HamiltonianH at low temperature and negative values of the chemical potential. If is sufficiently negative the Coulomb gas is approximately a perfect rare gas of charged particles, as expected. The interesting fact is that for higher (but still negative) values of the gas changes to a rare gas of some atom or molecule (which is most likely neutral). The type of molecule is determined by the ground state of the HamiltonianH —N with center of mass motion removed.Dedicated to Roland DobrushinWork partially supported by U.S. National Science Foundation grant DMS 8600748 (J.C.), PHY 85-15288-(A03) (E.L.) and DMS-8601978 and DMS-8806731 (H.-T.Y.)     

Acoustic properties of glasses at low temperatures and low frequencies

We generalize the low temperature expressions for the variation of the sound velocity and sound absorption in glasses due to structural defects for the case of arbitrary frequencies. In case ωτ₂ ? 1 our expressions reduce to well known results.     

低温低压氢等离子体的光谱分析

采用螺旋波激发氢等离子体,测得氢的Balmer线系前三条谱线的强度.利用二谱线法求电子温度Te,并由Hβ的Stark展宽得到电子密度Ne,简要分析了Te、Ne以及强度与各种参数之间的关系.     

Augmented low index waveguide for confining light in low index media

Guiding light in the low index region of a high refractive index contrast waveguide can be beneficial for many applications including sensing, nonlinear optics and electro‐optics. Existing methods to achieve this goal suffer from fabrication complexity, large loss, or poor optical confinement. We propose a simple structure to achieve a significant enhancement of light confinement in the low index medium. We explain the guiding principle of this structure using geometrical optics, and suggest a number of applications where this guiding structure can provide significant performance benefits. The combination of simplicity, ease of fabrication, and good confinement makes this waveguide an attractive choice for a wide range of applications. To illustrate this, we consider the integration of a nonlinear polymer with a silicon photonic waveguide, and show that significantly better performance with an easier fabrication process can be achieved using this new scheme.

     

Optical fibers with low nonlinearity and low polarization-mode dispersion for terabit communications

Refractive-index nonlinearities have negligible effect on the performance of short-haul fiber-optic communication links utilizing electronic repeaters. However, in long links, nonlinearities can cause severe signal degradations. To mitigate nonlinear effects, a new generation of fibers, referred to as large effective-area fibers, have been introduced in recent years. This paper reviews the latest research and development work on these fibers conducted by several research groups around the world. Attention is focused on a class of large effective-area fibers that are based on a depressed-core multiple-cladding design. Another important issue in long-haul and high capacity fiber optic systems is the polarization-mode dispersion (PMD) which has been recognized as a serious limiting factor. In this paper, an improved fiber design is proposed which, in addition to providing large effective-area and low bending loss, eliminates PMD due to elliptical deformation in the single-mode wavelength region. Furthermore, this design is allowed to provide a small chromatic dispersion about few ps/nmkm, in order to overcome four-wave mixing effects.     

A low cost PC based card for heat-capacity measurements at low temperatures

We describe a simple, low cost pc based card for the measurement of heat capacity using adiabatic calorimetry at low temperatures. This card provides the control pulse to the sample heater as well as trigger pulse to the nano-voltmeter which monitors the sensor voltage (Ge sensor, Lake Shore Inc., USA). We have also added a 12 bit DAC on this card and this is used for remote setting of the heater current of an old SHE (now Biomagnetic, Inc., USA, model CCS) analog constant current source. Although this card is used here for heat-capacity measurements, the same can also be used for thermo-power and thermal-conductivity measurements.     

Autocorrelation low coherence interferometry

This paper describes the development of a new modality of optical low coherence interferometry (LCI) that is called autocorrelation LCI (ALCI). The ALCI system employs a Michelson interferometer to measure longitudinal autocorrelation properties of the sample optical field and does not require a reference beam. As the result, there is no restrictions applied on the distance between the sample and the ALCI system, moreover, this distance can even change during the measurements. We report experiments using a proof-of-principle ALCI system on a multilayer phantom consisting of three surfaces defining two regions of different refractive indices. The experimental data are in excellent agreement with the predictions of the theoretical model.     

Magnetism in low dimensionality

The collective creativity of those working in the field of surface magnetism has stimulated an impressive range of advances. Once wary, theorists are now eager to enter the field. The present article attempts to take a snapshot of where the field has been, with an eye to the more speculative issue of where it is going. Selective examples are used to highlight three general areas of interest: (i) characterization techniques, (ii) materials properties, and (iii) theoretical/simulational advances. Emerging directions are identified and discussed, including laterally confined nanomagnetism and spintronics.     

g_1 at low x and low Q^2 with Polarized ep colliders

Measurements of at low x and low are expected to provide a sensitive probe of the transition from Regge to perturbative QCD dynamics, offering a new testing ground for models of small x physics. We discuss the potential of polarized ep colliders (Polarized HERA and eRHIC) to investigate this physics – varying between 0.01 and 1 GeV– and to constrain the high-energy part of the Drell-Hearn-Gerasimov sum-rule for polarized photoproduction. Received: 28 August 2000 / Revised version: 9 November 2000 / Published online: 21 December 2000