A compact wideband balun design using double‐sided parallel strip lines with over 9:1 bandwidth

A simplified miniaturized wideband balun design covering (0.38‐3.5 GHz) is presented. The broadband balun structure occupies a small area of 20.7 mm × 20.8 mm. The balun is designed using low loss double‐sided parallel strip lines and is comprised of a two‐stage Wilkinson divider followed by loading, symmetrically, the two output ports. One port with a phase inverter circuit; while a very similar but non‐inverting circuit is placed in the other port for loading‐balance compensation. To realize the balun's function, different smooth transitions have been employed and were accounted for. The fabricated balun circuit demonstrated phase and amplitude imbalance of less than ±5° and ± 0.4 dB, respectively, over the band.     

一种紧凑型和差比较器的设计

提出了一种应用于X波段的紧凑型和差比较器,其设计采用矩形同轴线形式。通过对实物的测试结果看出:该和差比较器在1 GHz的工作频带宽度内各端口电压驻波比不大于1.25,幅度不平衡度不大于0.2 dB,相位偏差不大于±3°;同时,其结构紧凑,易于工程实现,具有较强的实用性。     

应用多索引加法量化编码的近邻检索算法

目的 海量图像检索技术是计算机视觉领域研究热点之一,一个基本的思路是对数据库中所有图像提取特征,然后定义特征相似性度量,进行近邻检索。海量图像检索技术,关键的是设计满足存储需求和效率的近邻检索算法。为了提高图像视觉特征的近似表示精度和降低图像视觉特征的存储空间需求,提出了一种多索引加法量化方法。方法 由于线性搜索算法复杂度高,而且为了满足检索的实时性,需把图像描述符存储在内存中,不能满足大规模检索系统的需求。基于非线性检索的优越性,本文对非穷尽搜索的多索引结构和量化编码进行了探索新研究。利用多索引结构将原始数据空间划分成多个子空间,把每个子空间数据项分配到不同的倒排列表中,然后使用压缩编码的加法量化方法编码倒排列表中的残差数据项,进一步减少对原始空间的量化损失。在近邻检索时采用非穷尽搜索的策略,只在少数倒排列表中检索近邻项,可以大大减少检索时间成本,而且检索过程中不用存储原始数据,只需存储数据集中每个数据项在加法量化码书中的码字索引,大大减少内存消耗。结果 为了验证算法的有效性,在3个数据集SIFT、GIST、MNIST上进行测试,召回率相比近几年算法提升4%~15%,平均查准率提高12%左右,检索时间与最快的算法持平。结论 本文提出的多索引加法量化编码算法,有效改善了图像视觉特征的近似表示精度和存储空间需求,并提升了在大规模数据集的检索准确率和召回率。本文算法主要针对特征进行近邻检索,适用于海量图像以及其他多媒体数据的近邻检索。     

Study of compact microstrip lowpass filter with improved performance using defected ground structure

A compact lowpass filter (LPF) with wide stopband which uses four non‐uniform cascaded defected ground structure (DGS) units along with a 50 Ω microstrip line is reported in this article. Each DGS unit, which consists of a combination of three isosceles U‐shaped DGSs is analyzed in terms of an equivalent RLC circuit model. Every DGS of the DGS unit along with microstrip line provides one attenuation pole. It is found through performance comparison of the proposed U‐shaped DGS with dumbbell‐ and fork‐shaped DGSs that the proposed U‐shaped DGS is compact and provides higher quality factor. Further, the modeling of the proposed LPF is carried out using equivalent RLC circuit model. The results obtained through numerical and circuit simulations are compared. The proposed LPF has size of 14.44 mm × 3.4 mm, 3‐dB cut‐off frequency of 14.2 GHz, and greater than 40 dB and 22 dB stopband rejection up to 21.8 GHz and 30 GHz respectively. The proposed LPF is fabricated and experimentally tested. The experimental results are nearly in agreement with corresponding numerical/circuit simulation results.     

A folded dual‐mode bandpass filter with circular waveguide

In this article, a folded circular waveguide dual‐mode filter without tuning screws is designed for the fifth‐generation (5G) mobile communication system. The folded filter is composed of two stacked circular cavities operated at 3.5 GHz. Each cavity has two resonant modes, which can generate and control two transmission zeroes at specific frequencies. Through a coupling iris, the two single‐cavity filters are connected together, and can control four poles, which helps to expand the 3dB fractional bandwidth to 11.4%. The measured insertion losses are around 0.5 dB in the passband (from 3.4–3.6 GHz). The experiment results show an excellent agreement with the simulation results. Such folded filters have the advantages of very low insertion loss, compact size, high frequency selectivity, and low cost.     

跨入21世纪的高效节能新光源

自70年代以来,研究的新光源有带有红外反光镜的卤钨灯、紧凑型荧光灯、细管径直管荧光灯、陶瓷管金属卤化物灯、无电极放电灯和微波硫灯等,这些新光源将成为21世纪的主要光源     

算法到固定规模脉动阵列映射的有效方法

研究了算法到固定规模脉动阵列的映射过程,从提高处理器效率的角度对阵列进行优化,构造了阵列划分的代数表达式和算法,并证明了其正确性．研究表明,根据处理器效率,处理器间的通讯成本硬件开销等来优化处理器的数目,是实现算法到固定大小脉动阵列映射的有效方法．     

小波与多尺度分析

给出了小波的定义以及多分辨率分析的特点,指出了尺度函数与小波一起,决定了小波函数族的性质和特点,并给出了紧支集正交小波函数的构造特性,以及紧支集正交小波的性质,从而得出求解偏微分方程分层解的一种新方法,在解梯度变化较大的区域,可局部细化而不必对整个问题重新划分。     

500 kV紧凑型输电线路的舞动原因及防治措施

针对华北电网发生多条次500 kV紧凑型输电线路导线舞动掉闸故障,以500 kV海万紧凑型输电线路设备参数为依据,对紧凑型输电线路发生舞动的原因及治理措施进行分析和探讨。     

Scalability of a Hybrid Extended Compact Genetic Algorithm for Ground State Optimization of Clusters

We analyze the utility and scalability of extended compact genetic algorithm (eCGA)—a genetic algorithm (GA) that automatically and adaptively mines the regularities of the fitness landscape using machine learning methods and information theoretic measures—for ground state optimization of clusters. In order to reduce the computational time requirements while retaining the high reliability of predicting near-optimal structures, we employ two efficiency-enhancement techniques: (1) hybridizing eCGA with a local search method, and (2) seeding the initial population with lowest energy structures of a smaller cluster. The proposed method is exemplified by optimizing silicon clusters with 4-20 atoms. The results indicate that the population size required to obtain near-optimal solutions with 98% probability scales sub linearly (as Θ(n^0.83)) with the cluster size. The total number of function evaluations (cluster energy calculations) scales sub-cubically (as Θ(n^2.45)), which is a significant improvement over exponential scaling of poorly designed evolutionary algorithms.