Theoretical study of two-element array of equilateral triangular patch microstrip antenna on ferrite substrate

The radiation characteristics of a two-element array of equilateral triangular patch microstrip antenna on a ferrite substrate are studied theoretically by considering the presence of bias magnetic field in the direction of propagation of electromagnetic waves. It is found that the natural modes of propagation in the direction of magnetic field are left- and right-circularly polarized waves and these modes have different propagation constants. In loss-less isotropic warm plasma, this array antenna geometry excites both electromagnetic (EM) and electroacoustic plasma (P) waves in addition to a nonradiating surface wave. In the absence of an external magnetic field, the EM- and P-waves can be decoupled into two independent modes, the electroacoustic mode is longitudinal while the electromagnetic mode is transverse. The far-zone EM-mode and P-mode radiation fields are derived using vector wave function techniques and pattern multiplication approaches. The results are obtained in both plasma medium and free space. Some important antenna parameters such as radiation conductance, directivity and quality factor are plotted for different values of plasma-to-source frequency.     

Artificial antenna systems

The work describes experimental and theoretical results on the water oxidation in absence of an externally added potential, on the charge transport in organized microporous media and on the transport of excitation energy in an antenna system. Water oxidation to O₂ takes place at the solid/water phase boundary of a thin AgCl layer in the presence of a small excess of Ag⁺. This water oxidation step shows self-sensitization as the reaction proceeds, the sensitivity is extended from the near-UV-visible towards the red range. The quantum yield per redox equivalent for O₂ evolution upon illumination with near UV light (340–390 nm) is ∼ 0·8 and it is the same upon illumination with blue light (420–480 nm). In the green range it is ∼ 0·5. We discuss parameters controlling these reactions. Zeolite microcrystals are investigated as hosts for supramolecular organization of clusters, complexes and molecules. The possibility to arrange zeolite microcrystals of good quality and narrow size distribution as dense monograin layers on different types of substrates allows the discovery of specific properties. In the present context, three functionalities are of special importance intrazeolite ion transport, intrazeolite charge transport and intrazeolite excitation energy transport. All of them have been clearly demonstrated experimentally although there are still some controversies going on. Highly concentrated dyes have the tendency to form aggregates which generally show very fast radiationless decay. In natural antenna systems the formation of aggregates is prevented by fencing the chlorophyll molecules in polypeptide cages. A similar approach is possible by enclosing dyes inside a microporous material such that the volume of the cages and channels is able to uptake monomers only, but not aggregates. We know a number of materials bearing linear channels running through the whole microcrystal which allow the formation of highly anisotropic, monomeric dye assemblies. A few cases based on zeolite L as a host and the cationic dye molecules pyronine and oxonine have been investigated experimentally to some extent for this purpose. While the molecules can penetrate the channels, the geometrical constraints of this system excludes aggregation and therefore self-quenching up to very high concentrations, namely 0·2 M. Microcrystals with cylinder morphology and a size in the range of 100 nm have been found to be optimal for realizing collection efficiencies in order of 99%.     

Enzyme immobilization to ultra‐fine cellulose fibers via amphiphilic polyethylene glycol spacers

Ultra‐high specific surface cellulose fibers with an average diameter of 500 nm were generated from electrospinning and alkaline hydrolysis of cellulose acetate and used as porous supports for enzyme immobilization. The cellulose fiber surfaces were reacted with polyethylene glycol (PEG) diacylchloride to simultaneously add amphiphilic spacers and reactive end groups for coupling with a lipase enzyme. The quantity of reactive carboxylic acid on the fiber surfaces could be readily controlled by COCl/OH molar ratios and PEG lengths. The highest free acid (COOH) content of 1.0 mmol per gram of cellulose was obtained at 10 COCl/OH ratio with the 600‐Da PEG diacylchloride. Enzyme coupling on such PEG‐attached cellulose was optimal in the presence of a water‐soluble carbodiimide [1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC)] at a very low EDC/COOH molar ratio of 0.2 under acidic condition and at ambient temperature. Whereas the free lipase retained only 25% of its original activity, the fiber‐bound lipase possessed much superior retention of catalytic activity after exposure to cyclohexane (81%) and toluene (62%) and hexane (34%). The fiber‐bound lipase also exhibited significantly higher catalytic activity at elevated temperatures than the free form, that is, 10 times at 70 °C. The ultra‐fine, fibrous, and porous structures were retained throughout alkaline hydrolysis, activation, coupling, and activity assays. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4289–4299, 2004     

高频海态雷达双环天线调谐电容的计算

调谐双环天线是美国ＣＯＤＡＲ海态雷达探测天线的基本组成单元，适用带宽为２～３０ＭＨｚ．利用矩量法，结合网络理论，推导出其调谐电容和电流分布的计算公式，计算结果与有关文献实际测量的结果相符合．     

Tunable Chirped Fiber Grating Based Variable Time-Delay Network for Phased-Array Antenna Beamforming

In this paper, we present a photonics continuous beamforming system for optically controlled phased-array antenna based on a tunable fiber ring laser source and a novel variable true-time delay network consisting of one single-mode fiber delay line and four tunable chirped grating delay lines. The chirp rate of each chirped grating is tuned by bending a uniform fiber Bragg grating (FBG) bonded at a slant onto the lateral surface of a simply supported beam. This kind of variable true-time delay network can provide five-channel time-delayed signals that can be fed to an antenna array to achieve continuously beam scanning. The proposed true-time-delay unit with 5-element phased array steerer is suitable for phased-array antenna beamforming at frequencies up to 12 GHz.     

等离子体有源透镜天线的特性分析

 应用高功率微波大气传输机理和等离子体物理理论，提出了一种新概念天线-等离子体有源透镜天线。简要概述了其实现方法，并对其反射、透射、吸收、工作带宽和最佳工作频率等特性参数进行了分析与计算。该天线根据需要可聚束ＨＰＭ工作波，也可将外来入侵的ＨＰＭ波聚束后发送回原处，可形成空间有源滤波等器件。     

10 GHz,9 ps Pulses Generation from an Actively Mode-locked Fiber Ring Laser

１ＩｎｔｒｏｄｕｃｔｉｏｎＨｉｇｈｓｐｅｄａｎｄｌａｒｇｅｃａｐａｃｉｔｙａｒｅｔｈｅｅｖｉｄｅｎｔｆｅａｔｕｒｅｓｏｆｔｈｅｉｎｔｅｒｎａｔｉｏｎａｌｏｐｔｉｃａｌｃｏｍｍｕｎｉｃａｔｉｏｎｒｅｓｅａｒｃｈ．Ｈｏｗｅｖｅｒ，ｔｈｅｈｉｇｈｅｓｔｂ...     

Artificial Neural Networks for Resonant Frequency Calculation of Rectangular Microstrip Antennas with Thin and Thick Substrates

Neural models based on multilayered perceptrons for computing the resonant frequency of rectangular microstrip antennas with thin and thick substrates are presented. Eleven learning algorithms, Levenberg-Marquardt, conjugate gradient of Fletcher-Reeves, conjugate gradient of Powell-Beale, bayesian regularization, scaled conjugate gradient, Broyden-Fletcher-Goldfarb-Shanno, resilient backpropagation, conjugate of Polak-Ribiére, backpropagation with adaptive learning rate, one-step secant, and backpropagation with momentum, are used to train the multilayered perceptrons. The resonant frequency results obtained by using neural models are in very good agreement with the experimental results available in the literature. When the performances of neural models are compared with each other, the best result is obtained from the multilayered perceptrons trained by Levenberg-Marquardt algorithm.     

螺旋天线轴向长度对螺旋波传播、吸收的影响

采用有限元法数值求解Maxwell方程组,分析H-1仿星器实验参数下螺旋天线的轴向长度对螺旋波传播、吸收的影响。计算结果表明：随着螺旋天线轴向长度的增加,天线总辐射能量和辐射电阻逐渐增大;在H-1等离子体中螺旋天线主要激发m=±1模式波,其中m=-1模式波一般在等离子体边界传播;全波螺旋激发的波能量主要沉积在等离子体边界,导致等离子体径向能量较强的非均匀吸收,加热效果不理想;半波螺旋天线激发的波可深入主等离子体区域传播,等离子体径向能量吸收相对均匀,加热效果好。