Coherence length and noise properties of GaAlAs broad-band sources

The coherence length of two types of GaAlAs broad-band sources have been measured as a function of current. The noise properties of these devices were also measured in short path-length difference interferometers.     

Hybrid modes in corrugated conical horns with narrow flare angle and arbitrary length

By comparing the modified field equations of a corrugated conical horn of narrow flare angle (and arbitrary length) with those of a corrugated cylindrical waveguide, a technique to solve the characteristic equation of the horn is developed. It is also shown that the expressions for the far-field radiation pattern of the waveguide are applicable to the horn, except that the propagation constants must be modified.     

Corrugated horns

The corrugated horn has become the preferred choice of antenna for use in high-performance microwave reflector antennas for communications, radar and remote sensing. The principles and attributes of corrugated horns are explained. The analysis, design and manufacturing techniques and types of horns in use are briefly discussed     

Very wideband corrugated horns

An expression for the input impedance of a short-circuited, linearly-tapered transmission line is derived. The use of tapered slots in a corrugated horn is proposed as a means of broadening their bandwidth to greater than 3:1. Test results are presented for an experimental horn operating over the full 7.5?18 GHz range of DR14 waveguide.     

Gain of standard horns

A computer program has been developed to obtain the gain of standard horn aerials in the Fresnel and the far-field regions. The program is the computerisation of Braun's theoretical results on the gain of pyramidal horns, in which he considers the `intrinsic phase? error due to the horn slant heights and the `space phase? error due to the aperture of the horn.     

Phase-matched broad-band Raman amplifiers

The use of angle-tuned phase matching is shown by analysis and computer simulations to reduce limitations an the pump-laser bandwidth in Raman amplifiers of either near-collinear or crossed-beam geometries. This technique requires careful adjustment of the input beam angles and the use of prisms or gratings in the input and output beams. Simultaneous high conversion of multiple spectral lines or a broad-band spectrum can he obtained over a much wider range of temporal- and spatial-pump-intensity variations than in conventional designs. Intensity-phase print-through from multiple-line coupling can be significantly reduced, improving beam quality     

A broad-band twist reflector

Polarization twisting reflectors, or twist reflectors, consisting of a wire grid spaced approximately3 lambda/8from a ground plane [1], [2] have a bandwidth of at most 30 percent. It is shown that the inclusion of an additional wire grid in front of the first grid makes bandwidths of 100 percent possible. Design formulas, theoretical performance in terms of cross polarization attenuation, and some experimental results for a twist reflector with two wire grids are given.     

Self-organizing broad-band transport networks

In a self-organizing system, behavior emerges at the large scale from the collective interaction of simple rules that apply at the smaller scale. The behavior that emerges is not directly apparent from inspection of the local rules or processes operating at the lower level. Few problems in engineering have been addressed with the specific idea of designing simple rules that operate in an isolated local manner to derive a desired self-organizing side effect. Some specific telecommunication network control problems have been addressed with this approach, however, in areas where conventional approaches are suffering from the “software mountain ” phenomenon. In the applications of transport network restoration and traffic adaptation, this self-organizing approach promises better speed, accuracy, autonomy, and robustness than centralized control or explicit messaging-based distributed approaches. A key advance has been the development of a set of nodal rules for game-like operations on information tags (called statelets) borne on every link of the network. These rules spontaneously organize the resources of the transport network into a maximal set of simultaneously feasible paths between named points in the network. This process is adapted for restoration, provisioning, and traffic adaptation in a manner where the network is its own data base. The computational workload is distributed over the network as a whole, and external control is relaxed to focus only on large-scale tuning of what is operationally a self-organizing autonomous transport network. This paper is an applications oriented survey of the self-organizing concept and mechanism and its application to restoration, provisioning, network audit and traffic adaptation     

Deterministic broad-band PMD emulator

We present the architecture for a deterministic broad-band polarization-mode dispersion (DBPMD) emulator based on four stages. The first three stages of flexible frequency-dependent rotation provide the three degrees of freedom for emulating PMD at each frequency, while the fourth stage compensates for the isotropic dispersion created by the first three stages. We describe the algorithm to synthesize the required rotation angle of each stage using the PMD concatenation rules. Using numerical simulations, we demonstrate good fidelity of the DBPMD emulator in approximating randomly selected spectra of PMD vectors.     

Scales for rectangular horns

The scales presented are useful both for design of optimum horns for a given gain, and for finding the gains of rectangular horns from the dimensions. This article further illustrates the relationships among various parameters of rectangular horns. Although the design method started with a waveguide width-to-height ratio of 2:1, the method produces suitable designs for other waveguide ratios.     

Subcarrier multiplexed broad-band service network: a flexibleplatform for broad-band subscriber services

The concept of the subcarrier multiplexed broadband service network (SCM-BSN) has been developed in response to the need to provide low-cost integrated broadband services in the local loop. The SCM-BSN architecture incorporates three elements which have been identified over the past few years as key cost-saving features: passive optical splitting, fiber-to-the-curb, and subcarrier multiplexing of video signals. The SCM-BSN concept, a prototype system that has been built at the GTE Laboratories, and some possible evolutionary scenarios to integrated digital services are described     

Gain of corrugated conical horns

The absolute gain of a corrugated horn which is designed as a 100-GHz gain standard for the Crawford Hill 7-Meter offset reflector has been calculated and measured. The measured gain is determined from "three horn" transmission measurements. The other two horns are a TRG Model W869 corrugated horn and a dual mode horn. Correction factors were computed from the near field power transmission formula. The measured gain of the gain standard is30.8 pm 0.16 dB. Comparison between measured and calculated gains indicate very low ohmic loss in a corrugated horn. The condition of maximum gain for a given length has been found to be a half wavelength phase deviation in the horn aperture. Calculated gain data as well as near field correction factors for two identical corrugated conical horns are given here as reference information.     

Pyramidal horns at 460 GHz

Calculations and measurements of the beam patterns of pyramidal horns at 460 GHz are given. The calculated patterns show excellent agreement with experimental results.     

宽带业务的运营模式

从全国来看,宽带网络普遍存在“热建冷用”现象,宽带业务存在的问题主要有：1)在资费方面,目前的宽带计费方式很不灵活,用户对ISP收费存在不满和不信任情绪。收费方式不灵活,一般按时长收费或按包月制收费,用户普遍认为宽带收费过高,而且上网时间少时,包月不划算。2)内容服务方面,宽带网上的内容还是传统窄带业务内容,大大降低了对客户的吸引力,用户除了感到上网速度快以外,并没有体会到宽带网络的更多优势,值得付费的信息少。     

全球宽带管制趋势

介绍了宽带的含义和全球宽带用户分布情况,论述了管制机构应扮演促进宽带发展推广的角色,提出通过引入竞争、促进宽带市场发展的频谱管理机制、调整管制政策等措施,为宽带网络、业务的发展创造有利的环境.     

Design of profiled corrugated horns

The design principles used to realize smoothly profiled corrugated horns are described. The smooth profiling causes power to be converted to higher order HE₁₂ modes which radiate to produce high sidelobes in the copolarization patterns. A computer-aided spherical modal-matching technique is used to study the higher-order mode conversion. The results show good agreement with measurements. A profiled horn using a series of discrete conical sections is proposed to eliminate most of the mode conversion. A horn designed in this way is presented and shown to possess improved performance characteristics in comparison to a smoothly profiled design     

如何组建宽带城域网

讨论和分析了宽带城域网的由来和概念、业务定位、主要技术，并从传统和新兴的两类不同运营商的角度出发，探讨和研究了宽带城域网的技术选择策略、方法以及典型组网模式。     

Radiation from wide-flare-angle scalar horns

The radiation pattern of a wide-flare-angle scalar horn is determined by a modal-expansion technique and also by the Kirchhoff-Huygen method. Both approaches lead to similar results which agree well with experimental patterns obtained previously by Kay.     

单相短柱型直线超声电机的设计

提出了一种单相驱动的立式短柱型压电直线超声电机,论述了该电机的动作原理和设计过程。该电机利用纵向振动和横向振动的耦合模态工作。为获得同一驱动频率的一致的双向运动特性,该电机采用对称结构,利用压电陶瓷在短路和开路时弹性模量存在差异的特性,用单相驱动信号实现了纵向和弯曲耦合模态的有效激发。以增大电机弯曲振动模态前后振幅比为目标,利用三自由度集中质量的简化模型,优化了定子的结构。制作了电机的原理样机,对其进行了输出性能测试。实验结果表明,电机的输出性能良好。电机定子长22 mm,自重3.3 g,0.3 N输出推力下最大速度达140 mm/s,5 N预压力下最大输出推力近1 N。     

Stable broad-band microwave amplifier design

A modified real-frequency technique for designing a broadband microwave amplifier with guaranteed stability is presented. This method generates the two sets of resistive excursions necessary for synthesizing the source and load admittances of the amplifier concurrently, rather than sequentially, while both the stability and realizability requirements are satisfied simultaneously. Regardless of its constrained nature, the method has been formulated as an unconstrained optimization problem. An 8-12-GHz-band amplifier design example is presented to demonstrate its application. The transducer power gain obtained in the example by this method is 11.3±0.4 dB, which is 2.6-dB higher than that obtained by using the real-frequency technique