An overview of frequency synthesizers for radars

The authors present an overview of frequency synthesizer techniques suitable for radar systems. Various synthesizer architectures and key synthesizer components are considered along with a discussion of advantages and disadvantages. Some architectures are hardware intensive and, because of their physical size, are more suitable for stationary or shipboard radars. Architectures requiring smaller volume are more suitable for airborne applications. Direct, phase-locked, and frequency-locked architectures are covered, including key building blocks and performance limitations. The direct digital synthesizer (DDS) architecture is considered briefly, as it is not yet widely used in radar systems. Finally, projections are made of advances in components that have a direct effect on frequency synthesis     

A practical method of coefficient computation for a microprocessor-controlled variable recursive digital filter

The synthesis of general-type recursive digital filters from analog prototypes may require complicated computations not suitable for filter structures where the coefficients are to be evaluated by a microprocessor control unit. A general synthesis procedure suitable for the application to such structures is described and some design examples are reported.     

Power and area-optimised Carry-Select Adder architecture for standard cell-based design

A Carry-Select Adder (CSA) is one of the most suitable adders for high-speed applications, but the power and area penalties are greater, because it requires a double Ripple-Carry Adder (RCA) structure corresponding to carry inputs 0 and 1. Current low-power and low-area techniques are not suitable for a standard cell-based design which is one of the widely adopted design methodologies. Our work proposes two simple optimised architectures suitable for standard cell-based designs. A simple decision logic that replaces the RCA for Carry input 1 in a conventional CSA is proposed. One of the proposed architectures reduces power and area significantly with a small delay penalty compared to the existing techniques. Another proposed architecture improves the speed of operation and reduces the power and area considerably. The first one is more suitable for high-speed arithmetic in battery-operated applications where there is a trade-off between speed and power, while the other one is suitable for high-performance applications which also require area and power optimisation. The proposed architectures were implemented in TSMC 0.18um CMOS technology, and compared with conventional Square Root Carry-Select Adders and an existing standard cell-based design.     

A comparison of deconvolution techniques for the ultrasonicnondestructive evaluation of materials

Several major deconvolution techniques commonly used for seismic applications are studied and adapted for ultrasonic NDE (nondestructive evaluation) applications. Comparisons of the relative merits of these techniques are presented based on a complete set of simulations on some real ultrasonic pulse echoes. Methods that rely largely on a reflection seismic model, such as one-at-a-time L(1) spike extraction and MVD (minimum variance deconvolution), are not suitable for the NDE applications discussed here because they are limited by their underlying model. L(2) and Wiener filtering, on the other hand, do not assume such a model and are, therefore, more flexible and suitable for these applications. The L(2) solutions, however, are often noisy due to numerical ill conditions. This problem is partially solved in Wiener filtering, simply by adding a constant desensitizing factor q. The computational complexities of these Wiener filtering-based techniques are relatively moderate and are, therefore, more suitable for potential real-time implementations.     

Automation of the synthesis of asynchronous sequential circuits

The automation of a method for synthetising asynchronous sequential circuits is reported. The method is suitable for circuits having transition and level inputs. Inclusion relations between state-pair sets and partitions are used for the selection of suitable partitions for an economic race-free state assignment of minimum transition time.     

用于背投电视的LED光源

发展了一种带初级光学元件的新型LED光源，其亮度水平已适合将来背投电视的要求。讨论与此种LED封装性能密切相关的议题：基础的芯片技术、合适的的封装设计和初级光学元件。同时也介绍了在背投电视中使用LED光源的一些优点。     

Multiwavelength lightwave networks for computer communication

The different approaches being considered to build high-capacity lightwave networks are described. Two kinds of lightwave network architectures are examined: broadcast-and-select networks and wavelength-routing networks. A comparison of the two shows that broadcast-and-select networks may be more suitable for local area networks (LANs) and metropolitan area networks (MANs), while wavelength-routing networks are suitable for wide area networks (WANs). The overall network may then be a combination of broadcast subnets interconnected by a point-to-point wavelength-routing network     

微波设备表面电磁泄漏位置检测方法研究

针对微波设备表面电磁泄漏位置的检测方法进行研究,根据其表面等效辐射源形式的不同,设计了不同的检测方法,并提出了相应的实验测试方案.其中,综合孔径被动辐射计成像的方法适用于表面等效辐射源为非相干源的情况;数字透镜相移成像的方法适用于表面等效辐射源为相干源的情况;物理透镜成像的方法适用于表面等效辐射源为非相干源、相干源和部分相干源的全部三种情况.     

Activity function for DCT coded images

By combining a measure of activity in transform-coded image blocks with frequency sensitivity data, suitable psychovisual coefficient quantisation step sizes can be calculated. A number of possible definitions for an activity function A/sub F/ are proposed. The most suitable of these is determined by comparing results on a subjective basis.<>     

下一代互联网中名系统的研究

学术界近期提出了基于扁平结构的分布式哈希表（DHT）名系统,用以克服现有名系统域名解析系统（DNS）存在的缺陷,如不支持数据的移动、复制等,但由于其解析时延较大,不适于实际应用。为此,综合DNS名系统及DHT名系统的优点,设计了两种新的系统：第一种系统采用One-hop DHT形式,三层环结构实现,适于小环境应用;第二种采用混合结构DHT形式,分域实现,适于全球性应用。经理论分析证明这两套系统在实际应用中是可行的。     

The realization of the effect of nonuniform distribution in semiconductor null networks

Uniform and nonuniform distributed semiconductor devices suitable for null networks were experimentally fabricated and the effect of nonuniform distribution was observed. The temperature sensitivities were measured and compensating circuits are given. The devices are of wide application and suitable for integrated circuit fabrication.     

Field Theory Design of Rectangular Waveguide Broad-Wall Metal-Insert Slot Coulplers for Millimeter-Wave Applications

A design theory for broad-wall metal-insert slot couplers suitable for an inexpensive and very accurate metal-etching manufacturing technique is described. The method of field expansion into suitable eigenmodes used considers the effects of finite insert thickness and higher order mode interaction at the step discontinuities. Computer-optimized design data for -3-dB couplers in the Ka- and W-bands are given. The data of the Ka -band design are transferable into the U- and V-bands by suitable frequency scaling calculation. Since the metal-etching technique is also advantageously applicable for couplers in the centimeter wavelength range, optimized design data for E-plane slot couplers in the often used Ku- and R120-waveguide-bands are included in the tables given. A Ku-band metal-etched four-slot coupler prototype achieves a +-1dB bandwidth of the -3-dB coupling of about 2 GHz, together with -36-dB isolation. The measurements show good agreement with theory.     

Investigation of Simulated annealing, ant-colony optimization, and genetic algorithms for self-structuring antennas

A self-structuring antenna (SSA) is capable of arranging itself into a large number of configurations. Because the properties of the configurations are generally unknown at the onset of operation, efficient search algorithms are required to find suitable configurations for a given set of environmental and operational conditions. This paper investigates the use of ant-colony optimization, simulated annealing, and genetic algorithms for finding suitable antenna states. The implementation of each algorithm for SSA searches is described, and the performance of each algorithm is compared to a random search.     

Active inductances using current conveyors and their application in a simple bandpass filter realisation

An active grounded inductance using a single second generation current conveyor (CC II) as the active element and three passive components is proposed. The inductance is seen to be suitable for moderate-Q applications. For high-Q with independent Q-controlled inductances suitable circuit techniques pertaining to the introduction of a second CC II as a voltage follower are also presented.     

Optimization of Multi-layer AR Coatings for GaInP／GaAs Tandem Solar Cells

The AR coatings for GaInP/GaAs tandem solar cell are simulated. Results show that, under the condition of the lack of suitable encapsulation, a very low energy loss could be reached on MgF2/ZnS system;in the case of glass encapsulation,the Al2O3/ZrO2 and Al2O3/TiO2 systems are appropriate choice; for AlInP window layer,the thickness of 30nm is suitable.     

A superconducting magnet system for free-electron cyclotron maser

A superconducting magnet system for free-electron cyclotron maser is developed. This system includes a main superconducting magnet, a gradient superconducting magnet, a normal magnet, a cryostat and some accessories. The designed magnet system has the advantages of having a small size, high stable magnetic field and suitable field profile. It is very suitable for a 4mm wavelength free-electron cyclotron maser. The design and some experimental results are given.     

Coherent lasers turn up the power

Three categories of multiwatt, coherent laser designs are discussed. The designs are single-mode waveguides suitable for output powers in the order of 200 mW, single-mode operation of multimode lasers, which are suitable for operation between 0.5 and 1.0 W, and the monolithically integrated master-oscillator power amplifier (M-MOPA) designs that have demonstrated 4.5 W of spectrally coherent output power and more than 0.8 W of single-lobe diffraction-limited output power in a technology that is scalable to even higher output powers. Laser-diode design architectures and the unique properties of semiconductor materials are reviewed     

Iterative reconstruction-reprojection and the expectation-maximization algorithm

The iterative reconstruction-reprojection (IRR) algorithm is a method for estimating missing projections in computed tomography. It is derived as an expectation-maximization (EM) algorithm that increases a suitable likelihood function. The constraint that the data form a consistent set of projections is loosened to require only that the means of the data form a consistent set, thereby suggesting that the algorithm is suitable for use with noisy data. Proofs of convergence to a stationary point and of monotonicity of the sequence of iterates are given. Simulations supporting these results are described.     

Iterative Soft Parallel Interference Cancellation for Convolutional-coded DS-CDMA System

We propose the use of soft feedback estimates for the PIC detector in aDS-CDMA system with FEC. The soft estimates are computed by the a posterioriof the log-MAP decoder. We compare this method with the conventional methodof using tentative hard decisions to perform interference cancellation at eachstage. Simulations under AWGN and multipath asynchronous channels areperformed for comparison. We supply a suitable a posteriori for the log-MAPdecoder, and obtain a suitable soft feedback from the decoder.     

Nonnumeric applications of microprocessors

Two nonnumeric applications of microprocessors are described. It is shown that commercially available products allow an economical design of a small private automatic branch exchange (PABX). The second application considers a laboratory data aquisition system. Microprocessor characteristics are assessed on the basis of our experience with these applications. In view of some of the shortcomings of current products, some sugsestions are made which would make microprocessors more suitable for the nonnumeric environment. To demonstrate the feasibility of these suggestions, a design of a suitable micro-processor is proposed.