宽带消色差红外光学超构透镜研究进展（特邀）

超构透镜是由亚波长散射单元结构排列而成的具有聚焦功能的平面二维超构表面。超构表面能够在亚波长尺度上操控光场的振幅、相位、色散和偏振态,是近年来迅速发展起来的新型光场调控载体。亚波长共振纳米结构使得高阶衍射被抑制,入射光场可以完美地被调制到设计的衍射级次上,从而确保了超构表面器件具有高的光子调控效率。同时,超构单元在设计上的灵活性及其特定的电磁响应使得超构表面可以实现对光场多个维度的定制化操控。不同于传统光学透镜依赖光传播的相位累积效应,宽带消色差超构透镜通过对光场相位和相位色散的同时独立调控解决了传统通过级联多个透镜修正色差造成的光学系统复杂和体积庞大限制,为发展小型化片上集成光学提供了全新的思路。文中围绕超构透镜的相关研究,首先介绍了超构表面调控光场振幅、相位和偏振态的基本原理,在此基础上,重点回顾了近年来关于超透镜的研究发展,包括通过单一参量调控的单波长超透镜的实现,以及通过对光场偏振、相位及相位色散的多参量联合调控的多功能宽带消色差超构透镜的发展现状,最后讨论其进一步发展的可能挑战与应用前景。     

频域宽带波束形成器优化设计

将常规频域宽带波束形成运用到电子战侦察系统存在一个问题：分块DFT处理会造成时域输出波形在块衔接处产生周期性失真,影响系统对信号时域参数的检测。为解决上述问题,在分析失真产生原因的基础上提出采用交叠DFT处理对传统方案予以改进,该方法首先对预处理数据进行交叠分段,再完成DFT运算及后续窄带处理。最后的仿真通过对比改进前后方案时域输出波形的保真度,验证改进后方法能有效缓解时域输出波形失真对系统的影响,并为工程实现提供了依据。     

宽波段凸面闪耀光栅优化设计

凸面闪耀光栅是研制高光谱分辨率成像光谱仪的关键元件之一,一般凸面闪耀光栅的有效波段范围较窄,较难满足宽波段成像光谱仪对光栅衍射效率的需求。为拓宽仪器观测波段,对其中凸面闪耀光栅进行了优化设计。以0.4~2.5 m波段Offner型成像光谱仪为例,研究了凸面光栅单衍射级和双衍射级共路两种色散结构,采用分区闪耀光栅和双角闪耀光栅来提高宽波段范围内的衍射效率。优化设计了两种双闪耀光栅在不同色散结构下的槽形,用标量理论和有限元分析等方法对光栅衍射效率进行了计算。结合仪器信噪比,给出了满足成像光谱仪不同需求时所适用的光栅。     

Data gathering via mobile sink in WSNs using game theory and enhanced ant colony optimization

Optimal performance and improved lifetime are the most desirable design benchmarks for WSNs and the mechanism for data gathering is a major constituent influencing these standards.Several researchers have provided significant evidence on the advantage of mobile sink (MS) in performing effective gathering of relevant data. However, determining the trajectory for MS is an NP-hard-problem. Especially in delay-inevitable applications, it is challenging to select the best-stops or rendezvous points (RPs) for MS and also to design an efficient route for MS to gather data.To provide a suitable solution to these challenges, we propose in this paper, a game theory and enhanced ant colony based MS route selection and data gathering (GTAC-DG) technique.This is a distributed method of data gathering using MS, combining the optimal decision making skill of game theory in selecting the best RPs and computational swarm intelligence of enhanced ant colony optimization in choosing the best path for MS. GTAC-DG helps to reduce data transfer and management, energy consumption and delay in data delivery. The MS moves in a reliable and intelligent trajectory, extending the lifetime and conserving the energy of WSN. The simulation results prove the effectiveness of GTAC-DG in terms of metrics such as energy and network lifetime.

     

基于最坏情况性能优化的稳健自适应宽带波束形成

针对期望信号导向矢量失配会导致自适应波束形成算法的性能急剧下降这一问题,提出了一种新的基于最坏情况性能优化的稳健自适应宽带波束形成方法。该方法通过将实际期望信号的导向矢量约束于不确定集合中,来提高算法的稳健性;同时增加阵列空间响应偏差的二次型约束,可避免引起信号有较大失真。计算机仿真结果表明:该方法不仅能够抑制导向矢量偏差所带来的影响,有效控制波束主瓣区域内信号的畸变和旁瓣区域电平,还改善了阵列输出的信干噪比,使其更接近最优值。     

N-channel depletion-mode InP FET with enhanced barrier height gates

The fabrication of an n-channel depletion-mode InP field-effect transistor (FET) with enhanced barrier height gates, using a surface passivation technique that substantially increases the barrier height (Φ_b=0.83 eV) of InP, is reported. The transistors demonstrate characteristics with excellent pinch-off, flat saturation, transconductance in the range of 60-68 mS/mm, and no indication of the onset of breakdown for drain-source biases in excess of 35 V. They are shown to be highly stable, with no observable drain current drift over a period of more than 24 h of testing under DC bias. The high stability and performance of these devices demonstrate the potential for the gate metallization of InP     

5G enhanced mobile broadband multi-criteria scheduler for dense urban scenario

Telecommunication Systems - Mobile communication networks have entered a new age by introducing fifth-generation technologies (5G). The International Union of Telecommunications (IUT) proposes new...     

自主创新导向下的宽带无线通信网络优化及发展策略思考

历经“．COM”泡沫及全球电信产业低迷之后，人们对“宽带”、“宽带无线”及“3G”、“WiMAX”等技术已开始持较理性的态度进行分析、思考与处理。当今，围绕NGN问题的讨论，人们探索了一系列以IP为基础的新一代网络的重要课题，包括：QoS性能、安全性、智能网管改进、可赢利商业模式及向FMCIMS／SIP多业务网络平滑演进的务实途径，这是一种前后向兼容、有效创造增值效益的演进。而下一代或新一代宽带无线移动（NGBWM）亦将按这一概念向前发展，特别是从个性化与个体化含义上看，未来NGN及GII的接入与应用层面，必将是包括卫星通信及其应用在内的无线通信的世界。     

基于凸优化的宽带雷达波形优化方法

针对宽带雷达目标识别波形优化中多类目标方位和初相不确定问题,在高斯色噪声背景下提出一种基于凸优化的波形优化方法。该算法通过半正定松弛方法对目标识剐波形优化这个非凸问题进行近似求解,较好地解决了多类目标方位和初相不确定情况下的波形优化问题。仿真结果表明：该方法可以有效增加各类目标之间的可分性,从而提高目标识别性能。     

城市宽带网络服务质量优化方法研究

随着网络承载业务的不断增加,对网络服务质量进行优化很有必要。文中简述了城市宽带网络服务质量的概念与衡量指标,以中小城市宽带网络优化为背景,分析网络服务中存在的问题,研究各种网络优化技术,探讨网络服务质量模型,为实现更好的宽带网络服务质量保证机制提供理论依据。     

Wide-ratio broadband SiGe HBT regenerative frequency divider enhanced by differential TIA load

A regenerative frequency divider with a differential transimpedance amplifier (TIA) active load using 0.35 mum SiGe HBT technology is demonstrated. The differential TIA is beneficial for higher frequency and lower sensitivity operation, and the inductive peaking enhances the bandwidth of the output buffer. From the experimental results, the operating frequency ranges from 5 to 27 GHz (fmax/fmm =5.2) for a supply voltage of 5 V and core power consumption of 49.5 mW. The chip size is 0.86 x 0.822 mm.     

Gradient-based adjoint-variable optimization of broadband microstrip antennas with mixed-order prism macroelements

This paper describes a new finite element method (FEM)-based adjoint-variable approach to design and optimization of planar microwave circuits using sensitivity analysis, with respect to small variations of their design parameters. The implementation is based on a specially developed class of mixed-order prismatic macroelements, suitable for an efficient analysis of planar microwave structures. Their use, combined with a simple probe feed model, not only reduces the overall computational effort but also facilitates a straightforward derivation of port parameter sensitivities. Explicit expressions are given for the adjoint solution and S-parameter sensitivity and the process is verified through the design and optimization of two slotted broadband microstrip patch antennas.     

Comments on "Surface wave enhanced broadband planar antenna for wireless applications"

For original paper see K.M.K.H. Leong et al., ibid., vol. 11, pp.62-4 (2001). The above paper claims to present "a new class of broadband antenna in which TE/sub 0/ surface-wave is used as the primary source of free space radiation". After reviewing the references, and analyzing the parameters published, it does not appear that the antenna can operate in the manner claimed.     

海洋背景下雷达测高优化的一种方法

雷达辐射波在传播过程中受海面对流层波导效应以及回波多径影响,波导效应导致雷达波束偏离真实位置;多径效应导致雷达阵面端回波幅度、相位矢量叠加,限制了雷达的测高精确度。针对岸基雷达海面方位测高精确度误差大,提出通过反演大气修正参数的方法提高雷达测高精确度。基于目标一次航迹信息、二次雷达高度信息,通过雷达测高公式拟合大气修正参数,将拟合后的大气修正参数代替雷达数据处理测高公式中的原k系数。通过Matlab软件统计海面方位大气参数修正前后雷达测高精确度的变化,实验结果表明,大气参数修正后雷达测高精确度提高了50.8%。     

Differential space-frequency modulation via smooth logical channel for broadband wireless communications

In this letter, a differential space-frequency modulation (DSFM) scheme is proposed for multiple input multiple-output (MIMO)-orthogonal frequency-division multiplexing (OFDM) systems in broadband wireless communications. We assume that the fading channels keep constant only within each OFDM block, and may change independently from one OFDM block to another. The differential schemes proposed for MIMO-OFDM systems in the literature cannot successfully decode with such a rapidly fading channel, since the successful decoding of the previously existing schemes relies on the assumption that the fading channel keeps constant within a period of several OFDM blocks, and it changes slowly from a period of several OFDM blocks to another. In our proposed DSFM scheme, the transmitted signals are differentially encoded in the frequency domain within each OFDM block. Thus, the differential decoding can be performed over subcarriers within each single OFDM block. Furthermore, if a statistical channel power-delay profile (PDP) is known at the transmitter, we propose to create a smooth logical channel to improve the performance of the DSFM scheme. We obtain the smooth logical channel by sorting the channel frequency responses over subcarriers from a statistical point of view. If the logical channel is not smooth enough, we further consider a pruning process in which we use only the "good" part of the channel and get rid of the "bad" part of the channel. Simulation results show that the proposed DSFM scheme over a smooth logical channel (with pruning, if necessary) performs well for various channel PDPs.     

Design of broadband microwave amplifiers with mixed-elements via reflectance data modeling

A practical method is introduced, to design single-stage broadband microwave amplifiers with mixed lumped and distributed elements via modeling the reflectance data obtained from lumped-element input and output matching network prototypes. The same transducer power gain level is obtained by using less number of lumped-elements in the mixed-element amplifier than that of the lumped-element amplifier prototype. A mixed-element amplifier design is presented, to exhibit the utilization of the method. It is expected that the method will be employed, to design microwave amplifiers for broadband communication systems.     

Integrating users into the wider broadband network via high altitude platforms

An overview of CAPANINA, a project funded by the European Commission's 6th Framework Programme, is presented. The project is developing communications technologies for use with aerial platforms with the aim of integrating users in hard to reach areas and those disadvantaged by geography into the wider broadband network. The article discusses the three broad areas of the project. Specific aspects covered include broadband applications and services selection, along with appropriate integrated delivery configurations to deliver the required capacity and upgradeability; and the associated trials, along with the required wireless and free space optical equipment. Longer-term research underway into delivering broadband backhaul to high-speed trains from aerial platforms, enabling integration with onboard WLAN access points, is also discussed.     

Nearly ideal enhanced barrier height Schottky contacts to n-InP for MESFET applications

The author reports the substantial enhancement of the Schottky barrier height of n-InP, using a new surface passivation process. Au contacts on the passivated surface resulted in nearly ideal Schottky diodes with barrier heights as large as 0.83 eV, ideality factors between 1.02 and 1.17 and high breakdown voltages. The passivation is found to promote the formation of a phosphorus oxide at the interface, which is believed to be responsible for the enhancement of the barrier height. The high quality of the contacts makes them ideal for InP MESFET gate electrodes.<>     

Low-complexity video coding via power-rate-distortion optimization

Wireless multimedia sensor networks (WMSNs) have been potentially applicable for several emerging applications. The resources, i.e., power and bandwidth available to visual sensors in a WMSN are, however, very limited. Hence, it is important but challenging to achieve efficient resource allocation and optimal video data compression while maximizing the overall network lifetime. In this paper, a power-rate-distortion (PRD) optimized resource-scalable low-complexity multiview video encoding scheme is proposed. In our video encoder, both the temporal and interview information can be exploited based on the comparisons of extracted media hashes without performing motion and disparity estimations, which are known to be time-consuming. We present a PRD model to characterize the relationship between the available resources and the RD performance of our encoder. More specifically, an RD function in terms of the percentages for different coding modes of blocks and the target bit rate under the available resource constraints is derived for optimal coding mode decision. The major goal here is to design a PRD model to optimize a “motion estimation-free” low-complexity video encoder for applications with resource-limited devices, instead of designing a general-purpose video codec to compete compression performance against current compression standards (e.g., H.264/AVC). Analytic results verify the accuracy of our PRD model, which can provide a theoretical guideline for performance optimization under limited resource constraints. Simulation results on joint RD performance and power consumption (measured in terms of encoding time) demonstrate the applicability of our video coding scheme for WMSNs.     

Heuristic optimization techniques for self-orientation of directional antennas in long-distance point-to-point broadband networks

A self-orientation system for a directional antenna is capable of determining the best orientation to receive the strongest wireless signal. In the event of two antennas being deployed randomly or deployed in a dense space where the effects of multipath and other wireless interference exist, efficient search algorithms are required to find the best orientation. Therefore, this paper presents four heuristic optimization techniques for the self-orientation of directional antennas in such events: Pattern Search method, Downhill Simplex method, DIRECT method, and Genetic Algorithm. The modification of each technique for this orientation problem is described, and the performance of each algorithm using different test cases with real world experiments is also described. From our study, we show that the Pattern Search method is the most suitable optimization technique for the self-orientation of directional antennas in long-distance point-to-point broadband networks.