小型雷达环境模拟器双波段快速跳频模块设计

设计了一种雷达环境模拟器高性价比双波段宽带快速跳频模块。采用DDS+倍频链技术,实现了输出射频信号在C、X波段的频率跳变。其频带较宽,跳频时间小于5μs,输出杂散抑制优于-50dBc,相位噪声优于-70 dBc/Hz@10 kHz,频率分辨率小于10 Hz,输出功率可控。该系统体积小、成本低,易于生产实现,可广泛应用于部队雷达的抗干扰训练和检测。     

宽带低噪遥感卫星模拟信号频综源技术研究

介绍了直接频率合成(DDS)的结构和原理;将DDS与杂散抑制技术应用于遥感卫星模拟信号源.在分析DDS谐波杂散信号影响的基础上,通过外部滤波网络和"余弦修正"等技术有效抑制了谐波杂散和噪声;实现了一种基于DDS+FPGA内置式可编程宽带低噪的频综源;实验表明该频综源具有频带宽(1 MHz～400 MHz)、频率分辨率高、切换速度快、相位噪声低等优点,满足通用型遥感卫星数据模拟源系统设计的需求.     

跳频通信宽频段频率合成器的分析与实现

设计和实现了一种高分辨率、低相位噪声、可用于快速跳频的基于∑-Δ调制的小数分频宽频段跳频频率合成器。主工作频率范围为1 800 MHz～1 900 MHz,辅助工作频率范围为600 MHz～820MHz,在偏离主频10 kHz时相位噪声优于-80 dBc/Hz,非谐波杂散小于-60 dBc,频率分辨率小于100Hz,换频时间小于50μs,这种新型频率合成器简单实用、性价比高,有广阔的应用前景。     

基于改进DDS算法的任意信号发生器设计

针对传统直接数字频率合成(DDS)算法存在的幅度量化误差、相位截断误差问题,提出了一种混合利用信号对称性+Sunderland构造对数据ROM进行压缩的方法,用来增大数据ROM的存储量,同时采用改进型相位抖动注入法抑制相位截断误差.硬件电路部分设计了幅频校正电路,对信号进行校正,保证了信号幅度的稳定输出.测试结果表明,信号发生器可以输出高速、稳定、低衰减、低杂散的任意波形,输出信号频率范围为1 MHz～30 MHz,幅度峰峰值为40 mV～6.7 V.     

基于DDS芯片的相位相关双通道信号源设计

采用直接数字频率合成(DDS)芯片AD9854设计了一种任意相位相关双通道信号源,利用FPGA可编程器件实现逻辑控制。该信号源可输出两路相干、同频、相位差可设定的正弦信号。同时,利用DDS器件内置的高速比较器及外围信号调理电路,也可同时输出三角波和方波信号。其输出频率范围为0¹50 MHz,频率分辨率为1μHz,相位调节分辨率可达0.022°。实测结果表明,该系统输出信号频率稳定度高、相位差精确。     

DDS杂散分析及抑制方法研究

频率源是现代雷达电子系统的重要组成部分,是整个雷达的心脏。直接数字频率合成器（DDS）具有频率转换快、频率分辨率高、输出频率相对带宽较宽、产生波形灵活、相位连续及体积小等优点,缺点是工作频率有限,杂散较高。分析在理想条件下DDS输出信号的频谱,在此基础上,分析并仿真影响DDS杂散噪声的原因,提出几种有效地抑制DDS杂散的办法,对改进DDS电路的杂散有很大的促进作用。     

神经网络正弦信号发生器

针对正弦信号发生器设计中，直接数字频率合成技术存在相位截断误差的问题，以神经网络为技术基础，以FPGA为硬件核心，提出了一种新型的高频正弦信号发生器设计方案，有效克服了上述问题。阐述了这种方案的工作原理、电路结构以及设计思路和方法。经过设计和仿真测试，系统的主时钟频率可以达到95 MHz且不占用ROM存储空间，输出的正弦信号为2.5 MHz时，输出信号的杂散抑制为80 dB，可见该方案资源占用率低，无相位截断，输出信号杂散小且输出频率较高。     

新型双环900M Hz、1800M Hz频段数字调谐系统

研究了DDS+双PLL构成的新型数字调谐系统:A环产生DDS所需的时钟信号,B环产生高频输出。B环使调谐器输出频率f0作较大变化,A环和DDS使f0作小变动。该系统工作频率为850MHz￣925MHz和1700MHz￣1850MHz,频率分辨率可达25kHz。在单片微机控制下,可实现跳频。     

基于DSP的短波跳频频率合成器的设计

针对传统跳频通信系统跳频器的频率转换速度慢、分辨率低等不足,设计了基于现代数字信号处理和直接数字频率合成技术的高性能跳频器,采用高速数字信号处理器(DSP)和直接数字频率合成器(DDS)来完成跳频器的功能,以m序列为跳频序列;DSP采用TI公司的TMS320VC5402,它一方面作为DDS芯片的控制器,控制DDS芯片的工作;另一方面产生m序列;DDS芯片采用ADI公司的AD9852,它在DSP的控制下完成频率合成,同时还可以实现数字调制;跳频信号输出后经测试系统进行检测,输出幅度随频率变化的阶梯波,以此来测试系统输出跳频信号的性能.     

基于FPGA的并行DDS

介绍一种提高直接数字合成器(DDS)系统时钟频率的并行处理方法。给出了一个基于现场可编程门阵列(FPGA)的具有400MHz系统时钟频率DDS电路的实现方法和实验测试结果。采用直接中频输出方式,输出频率范围250MHz～350MHz,频率分辨率6Hz,寄生信号抑制50dB。该DDS电路具有接口简单、使用灵活等优点,可用于雷达、电子战领域的宽带信号产生。     

Assessing Ideational and Evaluative Skills and Creative Styles and Attitudes

This article describes the rationale for the multiphase creative problem solving process, and reports the findings from an empirical investigation conducted to facilitate the problem solving of managers. The ideational skills of the managers were assessed before and after training in a complete process of creative problem solving, along with their ideational attitudes, creative problem solving style (i.e., generator, conceptualizer, optimizer, or implementor), and evaluative skill (i.e., ability to recognize original ideas). The most important findings indicated that the training had a significant impact on the evaluative accuracy of the managers. They were significantly more accurate in their judgments about original ideas after training, both in their identification of original ideas and their recognition of unoriginal ideas. After training, the managers also gave more solutions and more original solutions to problems. Finally, several variables (e.g., the “preference for active divergence” attitude, and the conceptualizer process style) seemed to moderate the impact of training. Training was therefore effective, with specific effects that can be predicted from pre-training individual differences in attitudes and process style.     

高等院校行政分析与决策系统的设计与实现

为提高高等院校的管理水平和决策水平,充分利用校园网资 源,开发了高等院校行政财政分析与决策系统。解决了诸如数据的动态查询、自动生成报表 、网络环境下数据共享等技术问题,具有网上数据共享、图形界面友好和安全的保密措施等 特点。     

Stochastic balancing and approximation-stability and minimality

A new method of stochastic model reduction has recently been introduced by Desai et al. [1], [2]. The stability of the reduced order model has not previously, been considered. In this paper, we show that the stability of the reduced order model follows directly from the results of Pernebo and Silverman [3]. It is also shown that the reduced order model is minimal, in the controllability/observability sense. The relevance of this notion of minimality to stochastic minimality is made clear.     

Semantics and verification of monitors and systems of monitors and processes

In this paper we present a sound and complete semantics for the monitor concept of C.A.R. Hoare. First a method for specification of monitors, introduced by O.-J. Dahl, is reviewed. This method is based on the relation between the historic sequence of monitor procedure calls and the historic sequence of monitor procedure exits. Based on such specifications and our new monitor semantics we present a method by which it is possible to prove that a concrete monitor is an implementation of an abstract one. In the last part of the paper an axiomatic semantics for systems of concurrent processes and monitors is introduced. The method supports verification by separation of concerns: Properties of the communication to and from each process are proven in isolation by a usual Hoare style axiomatic semantics, while abstract monitors are also specified in isolation by the method reviewed in the first part of the paper. These properties of the components of the system are then used in a new proof rule to conclude properties of the complete system. Stein Gjessing received a Ph.D. (actually a Dr. philos.) from the University of Oslo (Norway) in 1985. Presently he is an Associate Professor at the Institute of informatics, University of Oslo, Norway. Dr. Gjessings research interests are in the area of concurrent and distributed programming, operating systems, formal specification and verification and programming languages.     

Integrating and automating analysis and optimization

The development of an interface coupling program on personal computers for an analysis software system such as ANSYS, SAP, etc. and an optimization software system, MOST, is presented. By controlling and directing the communications the interface coupler integrates the two programs while retaining their versatility and interactive features. The integrated system is used to solve a numerical example of active noise control for a three-dimensional enclosure, in which an energy density level of control points is minimized by adding the sound source to cancel the unwanted noise. The interface coupling program automates with relatively low cost the iterative process for designing an engineering system, remaining flexible in acoustical modelling and efficient in equation solving. Also, the coupling interface is developed in a general-purpose way so that it can be expanded easily to integrate more analysis software packages of different kinds.