Langmuir flow effects in the laser gyro

Langmuir flow effects have been investigated in the laser gyro by measuring the integral of the beat frequency while tuning the frequency of oscillation. The results are in agreement with the traveling-wave Lamb model. The presence of the dc discharge tube walls gives rise to gas circulation in the laser gyro cavity. If the oppositely directed traveling waves see a net gas flow the gyro exhibits a null shift which depends on the magnitude and direction of the discharge current unbalance causing the net gas flow. The null shift is shown to be due to the mode pulling and pushing associated with the anomalous dispersion exhibited by the gain atoms.     

Reactively steered adaptive array using microstrip patch elements at 4 GHz

A reactively steered adaptive array (RESAA) has one element connected by a transmission line to a receiver and a number of closely spaced parasitic elements, each of which is terminated by an adjustable reactive load. The pattern is formed by control of the reactive loads. Experimental results and the theory are presented for a RESAA consisting of five microstrip rectangular patch elements resonant at 4.0 GHz. Using steepest descent control of the reactive loads in a power inversion mode (no reference), we find that a null with a depth of 30 dB (relative to the pattern maximum) and an angular width of about25degcan be steered towards an interferer. Typically, about 40 steps (iterations) are needed for forming the null. With the slow power meter and general purpose minicomputer that served as the controller, adaptation times of several seconds are required; extrapolation to a dedicated microprocessor controller predicts adaptation times of several milliseconds. Operation in a mode using a reference signal demonstrates that the pattern can be shaped to steer a null toward interference and a lobe towards a desired signal. The nulling bandwidth is approximately 40 MHz with this array. The advantages of a RESAA, as compared With a conventional adaptive array, include the elimination of the mixers and other hardware needed to perform the complex weighting of the output of each element at an intermediate frequency, and better pattern control for closely spaced elements. These advantages are obtained at the expense of a more complicated control algorithm.     

四频差动激光陀螺小抖动稳频工作模式判别技术研究

为避免传统光强差稳频方式的缺陷,提出了四频差动激光陀螺小抖动稳频方法。从四频陀螺工作原理出发,分析了小抖动稳频的可行性,其中工作模式判别问题是技术难点。提出三种解决方法：改变左右旋模频率间隔、光强差稳频方式的扫模电路结合、根据陀螺零漂数据来判别,为进一步研究提供了参考。     

Nonlinear two element active antenna array stability analysis

Closed form analytical equations for the stability condition for the two modes available within a two element active antenna linear array as the element separation is increased are presented for the first time. A mathematical explanation to the mode swap characteristics first reported by Stephan and Young (1988) is given with a prediction of within which mode the array will operate as a function of element separation. This knowledge is imperative since the array far-field radiation pattern is different depending on the operating mode, and so a prediction method is desirable (i.e. boresight null or peak). The identical element case is considered, although the analysis can be extended to incorporate similar though non-identical elements     

四频差激光陀螺由于稳频精度局限等引入的零漂

本文分析了四频差动激光陀螺由于稳频精度局限等原因造成其左右旋陀螺在增益曲线上不对称，并导致比例因子不对称和这种不对称的不稳定从而引入零漂的机理；还分析了影响它们的因素；并代入实验测得的稳频精度值，估测了产生的零漂大小。     

Computer analysis of vertical radiation patterns of dipole panelarray antennas

A GW BASIC computer program has been developed to analyze any azimuth vertical radiation pattern of a dipole panel array antenna, fixed on a square tower structure, under different conditions of horizontal progressive quadrature current phase shifting, mechanical panel displacement, beam tilt, feeding current coefficients (null filling) and asymmetric arrangements with and without panel centering. The final effects are singled out by comparing vertical radiation pattern diagrams corresponding to each condition. The result obtained in regard to simultaneous horizontal progressive current phase and mechanical shift show appreciable variations in the vertical radiation patterns, corresponding to arrays of one or two dipole per tower face (omnidirectional arrangement), while for more elements there is a negligible effect on the main beam, but noticeable changes on the sidelobes. On the other hand, for any omnidirectional arrangements under the forementioned conditions of current phase and mechanical shift, almost no vertical radiation is produced by an array of eight dipoles at 0° along the tower (compensation effect). For an array with binomial current coefficients, almost no changes on the beam pattern has been observed     

Single high-order transverse mode surface-emitting laser with controlled far-field pattern

Single transverse mode vertical-cavity surface-emitting lasers (VCSELs) with high output power are important for high-speed data links, optical recording, laser processing, and so on. We demonstrate a single high-order transverse mode VCSEL with narrow trenches formed on its top surface by using a focused ion beam. The formation of four straight cross trenches resulted in the selection of a stable LP/sub 41/ mode oscillation. A large far-field angle of the LP/sub 41/ mode, which causes a low coupling efficiency even with a multimode fiber, was drastically reduced by loading a phase shift layer. A single-lobe far-field pattern with low scattering loss was realized by loading a spatial phase shift of SiO/sub 2/. We evaluated a coupling efficiency with a single-mode fiber including its alignment tolerance. The controlled far-field pattern enables lens-free direct coupling with a single-mode fiber even for large active-area VCSELs.     

利用贴片天线的奇偶模实现宽频带辐射零点扫描

设计了一款方向图分集的宽频带贴片天线。该天线由矩形贴片与共面波导馈电结构组成。贴片工 作在偶模或奇模状态,分别对应边射和水平全向辐射方向图。两个辐射模式由一个尺寸为35 mm×14. 5 mm 的馈电 网络激励。馈电网络中的微带线-槽结构和共面波导(CPW)结构分别产生同向和反向电场,从而分别激励贴片的奇 模和偶模,实现宽频带和高隔离。测试结果显示,天线的工作频段为2. 17~2. 95 GHz,工作带宽为780 MHz(31%)。 基于这两个辐射模式,天线可在特定角度产生辐射零点以对抗恶意干扰,且零点的角度随工作频率的变化呈线性变 化规律。该天线可用于MIMO 等智能通信系统。     

一种基于遗传算法的唯相位宽零陷波束赋形方法

传统阵列方向图宽零陷形成技术需要对阵元施加复加权或者阵元位置扰动等复杂操作,实际实现比较困难。提出了一种基于遗传算法的唯相位波束赋形方法,针对宽零陷特点,结合均匀线阵方向图数学模型,设计一种适应度函数,优化阵元相位扰动值,最终获得符合要求的宽零陷阵列方向图。仿真结果表明,该方法可以在唯相位条件下形成较深的宽零陷,且零陷较平坦,收敛速度较快,稳健性较好。     

激光陀螺电路系统对其精度影响的实验分析

在四频激光陀螺高精度数字一体化电路的基础上,通过控制激光陀螺两臂放电电流差值、两臂电流和值、两对模式的光强差值分别按照预定程序进行精确的改变,从而得到以上参量与陀螺零漂之间的关系系数.对陀螺进行长时间的测试,根据实际工作中各参量的精度计算得出电路系统对激光陀螺精度的影响.实验中为保证结论的一般性,选取两个精度相差较大的激光陀螺进行实验,结果表明,在现有方式下工作的高精度数字一体化电路系统对激光陀螺精度的影响在1%以内.     

斩波稳零下自适应干扰对消系统的性能分析

分析了实际模拟自适应干扰对消系统中权值控制支路存在零漂时权值和误差的时域特性.零漂的存在易造成稳态权值偏离最优权值,导致干扰对消比显著下降,但不影响系统的平均收敛速度.斩波稳零法是克服零漂的主要方法,对采用基波斩波下系统的性能进行了理论推导,并通过仿真进行了分析.基波斩波导致系统成为时变系统,克服了零漂的同时,在权值中增加了新的频率分量,引入了新的干扰并导致干扰对消比有所降低.     

Solar panel scattering effects on reflector antenna performance

The effects of solar panel scattering on a Ku-Band reflector antenna performance are analysed. It is shown from computation and experiment that the solar panel scattering interference causes mainlobe gain decrease and sidelobe gain increase on the sum patterns, as well as null position shift and null depth decrease on the difference patterns     

The coaxial beam-rotating antenna (COBRA): theory of operation andmeasured performance

Many microwave generators, especially high-power sources, utilize an azimuthally symmetric output mode such as the TM₀₁ circular waveguide or the coaxial TEM mode. If such a mode is projected into an antenna aperture and radiated directly, then a doughnut-shaped radiation pattern with a boresight null will result. Antenna designs to directly accommodate an azimuthally symmetric output mode and the high electric fields of high-power sources have been considered, but they tend to be low gain, do not radiate a boresight peak along the axis of the source, and the pattern peak direction changes with frequency. Mode conversion techniques to alter the aperture field distribution have also been explored, but losses and weight, size and cost additions impact negatively on total system design. This paper describes a novel antenna we call the coaxial beam-rotating antenna (COBRA) that mitigates many of the problems normally associated with the azimuthally symmetric output modes of high-power microwave sources. The COBRA accepts directly an azimuthally symmetric guided mode of a microwave source and radiates a high-gain pattern with a boresight peak. In addition, the COBRA operates with a wide bandwidth, is compatible with the intense electric fields associated with high-power microwave sources, and the geometry of the antenna can be easily configured to produce an arbitrarily (elliptically) polarized boresight field. This paper presents the fundamental theory of operation, derives pertinent design and performance equations, and gives the measured operating characteristics of a COBRA prototype     

Coupled phase-shift distributed-feedback semiconductor lasers fornarrow linewidth operation

Mode properties of a coupled phase-shift distributed-feedback (DFB) structure are analyzed and the feasibility of narrow-linewidth emission is shown theoretically. The structure consists of a multiple number of phase-shift DFB laser units which are arranged in tandem and coupled with each other through additional phase shift of corrugation. Optimum structure parameters were determined for two coupled laser units so that the frequency detuning is zero and the mode pattern is the flattest. The mode analysis shows that the intensity distribution is flatter and the normalized coupling constant can be larger than those for the conventional DFB laser with a single phase shift. This indicates that the cavity length can be extended with less influence from the longitudinal spatial hole burning effect     

自适应天线方向图干扰零陷加宽方法研究

在自适应天线阵抗干扰的一些应用环境中，往往需要自适应天线方向图在对准干扰的位置形成宽的零陷从而增强算法的稳定性。本文从统计模型的角度出发，导出一种对干扰零陷加宽的自适应波束形成方法，该方法能在由于数据失配引起的干扰位置扰动的情况下有效地抑制干扰，大大增强了算法的稳定性，并且方法简单、所增的运算量很小。计算机仿真结果也证明了该方法的有效性。     

Design of array and line-source antennas for Taylor patterns with a null

An antenna pattern design technique which results in a generalized Taylor pattern, except in a narrow region where a deep null is formed, centered at a preassigned position is presented. It is shown how this technique can be applied effectively to both linear arrays and line sources. The approach is direct so that the technique does not use either iterative sampling or a perturbation procedure. It is particularly useful in the design of a large array with a prescribed deep null. Numerical results indicate that to steer such a null, adjustment of the excitation is necessary near the edges only.     

一种多模馈源的设计

介绍了一种X波段多模馈源的设计方法,采用多种的魔T形成和差网络,多模喇叭的波束宽度、零值深度与边沿照射电平结合天线的系统要求确定其结构尺寸,具有零值深、零点漂移小、隔离度高、驻波系数低及耐大功率的特点。     

A patch antenna for HIPERLAN

A patch antenna suited for indoor HIPERLAN is presented. The antenna operates in T M ₀₂ mode and its radiation pattern is omnidirectional in azimuth and has a null in the normal direction. An experimental prototype has been designed and tested. A 6.1% bandwidth of VSWR2 and 4.2 dB antenna gain were measured at 5 GHz band.     

On the use of kernel structure for blind equalization

The mathematical theory of kernel (null space) structure of Hankel and Hankel-like matrices is applied to the problem of blind equalization of cochannel signals. This approach provides a new perspective on the blind equalization problem and gives insights into the identifiability conditions already presented in the literature. An algorithm is presented that tracks the exact null space of the symbol matrix even in the presence of noise. This work exploits the shift structure in the oversampled channel output and the finite alphabet property of the signals. Previously, these two properties were used independently in a two-step (equalize then separate) process. A contribution of the new approach is that is allows simultaneous exploitation of both the shift structure and the finite alphabet property of the signals     

一种改进的宽零陷天线方向图合成方法

在自适应阵列天线抗干扰的一些应用环境中 ,往往需要天线方向图在干扰的到达方向上形成宽的零陷以增强算法的稳健性。该文对一种宽零陷天线方向图合成方法进行了研究 ,提出了通过对零点矩阵加权处理 ,使不同干扰方向上的零点深度可以分别调节的改进方法 ,降低了方向图的畸变程度。计算机仿真结果证明了改进的效果