分形环单元八木天线的特性

介绍了应用分形原理设计环八木天线,采用分形环单元来替代传统环八木天线的圆环或方环,利用分形图形的空间填充特性来减小横向设计尺寸,以实现天线的小型化设计.以中心频率为900 MHz的Minkowski分形环单元八木天线为例,说明了天线的设计过程,设计结果表明该天线具有较为理想的技术指标,同时,相对于传统的环八木天线,采用分形结构可以使尺寸明显减小.     

Synthesis of fractal patterns from concentric-ring arrays

A technique has been developed for the synthesis of fractal radiation patterns from concentric-ring arrays. A family of functions known as generalised Weierstrass functions, have been shown to play a key role in the theory of fractal radiation pattern synthesis. The authors examine the self-similarity relation of the array patterns     

Rotary traveling-wave oscillator arrays: a new clock technology

Rotary traveling-wave oscillators (RTWOs) represent a new transmission-line approach to gigahertz-rate clock generation. Using the inherently stable LC characteristics of on-chip VLSI interconnect, the clock distribution network becomes a low-impedance distributed oscillator. The RTWO operates by creating a rotating traveling wave within a closed-loop differential transmission line. Distributed CMOS inverters serve as both transmission-line amplifiers and latches to power the oscillation and ensure rotational lock. Load capacitance is absorbed into the transmission-line constants whereby energy is recirculated giving an adiabatic quality. Unusually for an LC oscillator, multiphase (360°) square waves are produced directly. RTWO structures are compact and can be wired together to form rotary oscillator arrays (ROAs) to distribute a phase-locked clock over a large chip. The principle is scalable to very high clock frequencies. Issues related to interconnect and field coupling dominate the design process for RTWOs. Taking precautions to avoid unwanted signal couplings, the rise and fall times of 20 ps, suggested by simulation, may be realized at low power consumption. Experimental results of the 0.25-μm CMOS test chip with 950-MHz and 3.4-GHz rings are presented, indicating 5,5-ps jitter and 34-dB power supply rejection ratio (PSRR). Design errors in the test chip precluded meaningful rise and fall time measurements     

一种新型类Vicsek分形多频天线的设计

在Vicsek结构的分形理论基础上进行了改进, 提出了一种具有良好空间填充性和自相似特性的新型类Vicsek分形天线, 并在接地板上引入缺陷地结构(Defected Ground Structure, DGS)来改善频率、抑制谐波, 得到了可以运用在无线局域网(Wireless Local Area Networks, WLAN)、全球微波互联接入(Worldwide Interoperability For Microwave Access, WiMAX)以及C波段卫星通信的四个频段.天线的谐振频率分别为2.45 GHz、3.46 GHz、5.8 GHz和7 GHz, 相应带宽为0.2 GHz(2.37~2.57 GHz)、0.49 GHz(3.2~3.69 GHz)、0.75 GHz (5.52~6.27 GHz)和0.56 GHz(6.68~7.24 GHz), 增益最高达到4.89 dB.天线的小尺寸及全向性辐射特性表明该天线能很好地满足便携式多频段移动设备的要求.     

Reactance-loaded short-backfire arrays: new results

The letter presents experimental data for modified reactance-loaded short-backfire arrays. It is shown that the use of a rectangular subreflector, in conjunction with a half-wave-length rim around the edge of the main reflector, results in a smaller and simpler structure having larger power gain, smaller beamwidth, and lower sidelobe levels.     

Planar arrays with square lattices and circular boundaries: sumpatterns from distributions with uniform, amplitude or very lowdynamic-range ratio

A combination of simulated-annealing methods with Kim and Elliott's (1988) generalization of the Tseng-Cheng (1968) distribution allows rapid synthesis of planar arrays with rectangular lattices, circular boundaries, and a very low dynamic-range ratio. These generate sum patterns with satisfactory characteristics     

Modulating transistor: a new class of semiconductor device

A new negative resistance transistor n+-p-p?-p structure, consisting of four layers with three electrodes, is reported. The negative resistance effect is due to bulk conductivity modulation. Common emitter, common collector and common base characteristics are described.     

Tunneling injection lasers: a new class of lasers with reduced hotcarrier effects

In conventional quantum-well lasers, carriers are injected into the quantum wells with quite high energies. We have investigated quantum-well lasers in which electrons are injected into the quantum-well ground state through tunneling. The tunneling injection lasers are shown to have negligible gain compression, superior high-temperature performance, lower Auger recombination and wavelength chirp, and better modulation characteristics when compared to conventional lasers. The underlying physical principles behind the superior performance are also explored, and calculations and measurements of relaxation times in quantum wells have been made. Experimental results are presented for lasers made with a variety of material systems, InGaAs-GaAs-AlGaAs, InGaAs-GaAs-InGaAsP-InGaP, and InGaAs-InGaAsP-InP, for different applications. Both single quantum-well and multiple quantum-well tunneling injection lasers are demonstrated     

A new construction of two-dimensional arrays with the windowproperty

It is shown how row-complete Latin squares and Tuscan squares can be used to construct nonbinary 1-D and 2-D arrays that have the u ×v horizontal and/or vertical window property for all sufficiently large windows. It is shown how binary arrays with a similar property can be derived. Since an array can only be a perfect map for one particular size of window, the arrays that are constructed are not perfect but nevertheless have several practical applications, among others in connection with the coding and transmission of pictures. The method is deterministic rather than stochastic, and the arrays derived contain an effectively random selection of the windows of each relevant size     

Aromatic polyureas: a new class of nonlinear optical polymer with large second-harmonic generation

The second-order nonlinear optical properties of aromatic polyureas are reported. From Maker fringe measurements, the nonlinear d/sub 33/ coefficient of poled polyurea films with and without pendant chromophores was found to be 20*10/sup -9/ esu and 12*10/sup -9/ esu, respectively, at 1.064 mu m. Aromatic polyurea having no pendant chromophores shows a cutoff wavelength of transmission at 307 nm which is the first example of organic NLO materials to be optically transparent at such low wavelengths.<>     

On a new class of quasi-orthogonal filters

In this article, a new class of quasi-orthogonal filters, based on the Legendre and Malmquist-type quasi-orthogonal polynomials, is presented. These filters are generators of quasi-orthogonal functions for which we derive and present all important properties and relations. Our article is based on the classical theory of orthogonality and orthogonal functions, and also on new results in this field of mathematics. Based on theoretical results, we design schemes for the realisation of these filters. Finally, a trail quasi-orthogonal filter is practically realised and its quasi-orthogonality is proven by performing experiments. Quasi-orthogonal filters can be successfully used for signal approximation as well as for modelling, identification, analysis, synthesis and simulation of dynamical systems.     

Complete class of perfect binary arrays for 144 elements

A method has been proposed for building the complete class of perfect binary arrays having the size of 12×12 and its cardinality has been estimated.     

Grammar-based codes: a new class of universal lossless source codes

We investigate a type of lossless source code called a grammar-based code, which, in response to any input data string x over a fixed finite alphabet, selects a context-free grammar G_x representing x in the sense that x is the unique string belonging to the language generated by G_x. Lossless compression of x takes place indirectly via compression of the production rules of the grammar G_x. It is shown that, subject to some mild restrictions, a grammar-based code is a universal code with respect to the family of finite-state information sources over the finite alphabet. Redundancy bounds for grammar-based codes are established. Reduction rules for designing grammar-based codes are presented     

Spectral self-coherence restoral: a new approach to blind adaptivesignal extraction using antenna arrays

A new approach to blind adaptive signal extraction using narrowband antenna arrays is presented. The approach has the capability to extract communication signals from cochannel interference environments using only known spectral correlation properties of those signals, i.e. without using knowledge of the content or direction of arrival of the transmitted signal, or the array manifold or background noise covariance of the receiver, to train the antenna array. The class of spectral self-coherence restoral (SCORE) objective functions is introduced, and algorithms for adapting antenna arrays to optimize these objective functions are developed. Using the theory of spectral correlation, it is shown by analysis and simulation that these algorithms maximize the signal-to-interference-and-noise ratio at the output of the narrowband antenna array when a single communication signal with spectral self-coherence at a known value of frequency separation, along with an arbitrary number of interferers without spectral self-coherence at that frequency separation, are impinging on the array     

对一种具分形特征的电磁吸波材料的初步分析

研究了一种基于Salisbury屏的微波吸收材料,提出了一种具有Minkowski分形特征、表面加载阻抗的双方环形电磁带隙结构的吸波材料。该种材料具有薄、轻、吸收频带范围宽的优点,且吸波深度深于同等条件下没有分形特征的吸波材料。     

Possible new applications of periodic linear arrays

When the physical dimensions are adjusted properly periodic linear arrays, commonly known as Yagi-Uda arrays, may possibly be used as open waveguides or directional antennas operating at two or more widely separated frequency bands. Other applications include open low-pass or bandpass filters and open resonators.     

Adaptive arrays: A new approach to the steady-state analysis

Our main goal is a closed-form expression for the steady-state output signal-to-noise ratio (SNR) of ann-element adaptive array excited by one desired narrow-band signal andK - 1narrowband jammers. This is facilitated by representing each excitation by a complexn-dimensional vector-the excitation vector. We show that the important system parameters are functions of scalar products of pairs of these exctiation vectors. In particular, the normalized output SNR of the array is shown to be the ratio of determinants whose elements involve these scaler products. Such determinants are also shown to be involved in the expressions for the optimal array weights.     

对一个新的平方混沌类的研究

该文提出一个新的平方混沌类,计算了混沌类的李雅普诺夫指数,并对混沌类中结构III所表现出的环面破裂产生混沌和倍周期分岔产生混沌的现象进行了初步的研究,在同一个系统中可以观察到环面破裂和倍周期分岔两种不同的通向混沌的路线,这尚属首次报道。     

一种新型共边矩形环嵌套的分形多频天线设计

提出了一种新型分形结构的天线,该分形结构由多个共用一条边的矩形环嵌套构成。由于结构的自相似特性,使天线能够在多个频段工作。研究表明,天线的通频带个数由分形结构的矩形环个数控制,且各谐振频点与相应辐射单元的尺寸密切相关。设计了能同时工作在蓝牙、WLAN和WiMAX频段的三频天线,天线仿真的谐振频点分别为2.44GHz、3.55GHz和5.59GHz,相应的带宽分别为7.0%(2.35GHz-2.52GHz)、15.0%(3.28GHz-3.81GHz)和30.1%(5.13GHz-6.95GHz)。实物的测试结果与仿真结果基本吻合,符合设计要求。     

Electromagnetic reflection and transmission from a new version of Cantor fractal nonlinear multilayers

In this paper, we put forward a new version of Cantor fractal multilayers, which are nonlinear medium, and investigate its properties of reflection and transmission when a plane wave is obliquely incident upon it. A new exact self-similarity algorithm that make use of the self -similarity of these structure are developed. The results for different stages of fractal growth within the first-order nonlinear approximation are found. Compared with the traditional chain-matrix approach, the scheme provides the reflection and transmission coefficients for any stage (S) with much less calculation time on a personal computer.