An Error Equivalent Model of Revolute Joints with Clearances for Antenna Pointing Mechanisms

Joint clearances in antenna pointing mechanisms lead to uncertainty in function deviation. Current studies mainly focus on radial clearance of revolute joints, while axial clearance has rarely been taken into consideration. In fact, own?ing to errors from machining and assembly, thermal deformation and so forth, practically, axial clearance is inevitable in the joint. In this study, an error equivalent model(EEM) of revolute joints is proposed with considering both radial and axial clearances. Compared to the planar model of revolute joints only considering radial clearance, the journal motion inside the bearing is more abundant and matches the reality better in the EEM. The model is also extended for analyzing the error distribution of a spatial dual?axis("X–Y" type) antenna pointing mechanism of Spot?beam antennas which especially demand a high pointing accuracy. Three case studies are performed which illustrates the internal relation between radial clearance and axial clearance. It is found that when the axial clearance is big enough, the physical journal can freely realize both translational motion and rotational motion. While if the axial clearance is limited, the motion of the physical journal will be restricted. Analysis results indicate that the consideration of both radial and axial clearances in the revolute joint describes the journal motion inside the bearing more precise. To further validate the proposed model, a model of the EEM is designed and fabricated. Some suggestions on the design of revolute joints are also provided.

Two-step Structural Design of Mesh Antennas for High Beam Pointing Accuracy

A well-designed reflector surface with high beam pointing accuracy in electromagnetic performance is of practical significance to the space application of cable mesh reflector antennas. As for space requirements, cir- cular polarizations are widely used in spaceborne antennas, which usually lead to a beam shift for offset reflectors and influence the beam pointing accuracy. A two-step structural design procedure is proposed to overcome the beam squint phenomenon for high beam pointing accuracy design of circularly polarized offset cable mesh reflectors. A simple structural optimal design and an integrated structural electromagnetic optimization are combined to alleviate the beam squint effect of circular polarizations. It is imple- mented by cable pretension design and adjustment to shape the offset cable mesh surface. Besides, in order to increase the efficiency of integrated optimization, an update Broy- den-Fletcher-Goldfarb-Shanno （BFGS） Hessian matrix is employed in the optimization iteration with sequential quadratic programming. A circularly polarized offset cable mesh reflector is utilized to show the feasibility and effectiveness of the proposed procedure. A high beam pointing accuracy in order of 0.0001~ of electromagnetic performance is achieved.

An adjustment method for active reflector of large high-frequency antennas considering gain and boresight

The design of the Qitai 110 m Radio Telescope（QTT） with large aperture and very high working frequency（115 GHz） was investigated in Xinjiang, China. The results lead to a main reflector with high surface precision and high pointing precision. In this paper, the properties of active surface adjustment in a deformed parabolic reflector antenna are analyzed. To assure the performance of large reflector antennas such as gain and boresight, which can be obtained by utilizing an electromechanical coupling model, and satisfy them simultaneously, research on active surface adjustment applied to a new parabolic reflector as target surface has been done. Based on the initial position of actuators and the relationship between adjustment points and target points, a novel mathematical model and a program thatdirectly calculates the movements of actuators have been developed for guiding the active surface adjustment of large reflector antennas. This adjustment method is applied to an 8 m reflector antenna,in which we only consider gravity deformation. The results show that this method is more efficient in adjusting the surface and improving the working performance.

A new calibration model for pointing a radio telescope that considers nonlinear errors in the azimuth axis

A new calibration model of a radio telescope that includes pointing error is presented, which considers nonlinear errors in the azimuth axis. For a large radio telescope, in particular for a telescope with a turntable, it is difficult to correct pointing errors using a traditional linear calibration model, because errors produced by the wheel-on-rail or center bearing structures are generally nonlinear. Fourier expansion is made for the oblique error and parameters describing the inclination direction along the azimuth axis based on the linear calibration model, and a new calibration model for pointing is derived. The new pointing model is applied to the 40 m radio telescope administered by Yunnan Observatories, which is a telescope that uses a turntable. The results show that this model can significantly reduce the residual systematic errors due to nonlinearity in the azimuth axis compared with the linear model.

Effect of beam-pointing errors on bistatic SAR imaging

The purpose is to conduct a research in the energy variation of echo wave and the imaging effect caused by the aero bistatic SAR pointing errors. Based on the moving geometry configuration of aero bistatic SAR, a model of beam pointing errors is built. Based on this, the azimuth Doppler frequency center estimation caused by these errors and the limitation to the beam pointing synchronization error are studied, and then the imaging result of different errors are analyzed. The computer＇s simulations are provided to prove the validity of the above analysis.

无线光通信一对多发射天线研究进展

无线光通信是一种新兴的通信技术,具有高速、大容量和安全性好等优势。然而,传统的无线光通信系统存在着单对单通信模式限制,无法满足多用户同时通信的需求。无线光通信中光学天线起着发射和接收耦合光信号的作用,一对多点发射天线可以拓展无线光通信的应用。对国内外一点对多点光学天线的发展进行总结,介绍了一对多光学天线的基本原理。对目前现有的几种一对多光学天线设计方案进行讨论。最后对该领域的发展趋势和未来发展方向进行展望。

Spin Supercurrent in Phenomena of Quantum Non-Locality (Quantum Correlations, Magnetic Vector Potential) and in Near-Field Antenna Effect

It is shown that such phenomena as quantum correlations (interaction of space-separated quantum entities), the action of magnetic vector potential on quantum entities in the absence of magnetic field, and near-field antenna effect (the existence of superluminally propagating electromagnetic fields) may be explained by action of spin supercurrents. In case of quantum correlations between quantum entities, spin supercurrent emerges between virtual particles pairs (virtual photons) created by those quantum entities. The explanation of magnetic vector potential and near-field antenna effect is based on contemporary principle of quantum mechanics: the physical vacuum is not an empty space but the ground state of the field consisting of quantum harmonic oscillators (QHOs) characterized by zero-point energy. Using the properties of the oscillators and spin supercurrent, it is proved that magnetic vector potential is proportional to the moment causing the orientation of spin of QHO along the direction of magnetic field. The near-field antenna effect is supposed to take place as a result of action of spin supercurrent causing secondary electromagnetic oscillations. In this way, the electromagnetic field may spread at the speed of spin supercurrent. As spin supercurrent is an inertia free process, its speed may be greater than that of light, which does not contradict postulates of special relativity that sets limits to the speed of inertial systems only.

Analysis of Input Impedance of Asymmetrically Loaded Annular Ring Antenna

In this communication the numerical modelling for input impedance of an annular ring antenna is done. The cavity model is used for the analysis and the post is loaded asymmetrically at a point from the centre of the ring. The numeri-cal model formed is verified with the results of IE3D model based on method of moments. The loading of antenna can be used to design broadband antennas by enhancing the bandwidth of antennas.

Finite Element Modeling and Design of Rectangular Patch Antenna with Different Feeding Techniques

The finite element modeling of three dimensional structures is important for researchers especially in the field of antennas and other domains of electromagnetic waves. This paper presents a finite element calculations and numerical analysis for the microstrip patch antennas. In this paper, two different designs have been modelled and analyzed and both designs are based on the rectangular patches. The feeding point of one design is inside the patch while the other design contains feeding point outside the patch is T shaped. The computational analysis showed some interesting results for radiation pattern and far field domain. For these designs, the characteristic impedance taken is 50 Ω and the operating frequency domain is 1.4 to 1.7 GHz. The microstrip patch antennas are encapsulated in the inert spherical atmosphere of 20 mm thickness containing air inside it.

基于并联差速机构的通信天线及指向建模和跟踪方法

随着卫星星座互联网的发展及通信装备实战化升级换代,通信天线性能指标的要求越来越高。设计了一种基于并联差速机构的通信天线,介绍了通信天线的结构,分析了并联差速机构的原理,并进行通信天线指向建模和跟踪方法研究。在研究中,定义了运动数学模型,推导了解析式,进而得到跟踪方法。相较于传统采用串联驱动结构的通信天线,基于并联差速机构的通信天线具有刚度大、体积小、指向精度高等特点,在民品通信和军用通信领域具有良好的适用性。

环境风载荷下大口径反射面天线波束指向分析

大口径反射面天线是深空探测、卫星通信的关键设备。为了不断提高观测性能,天线口径不断增大,进而对天线指向精度的要求越来越高。随着天线口径的增大,天线的刚度降低、迎风面积增大,这会导致天线的柔性变形严重,性能难以保证。为探究环境风载荷下大口径反射面天线的柔性变形对电性能的影响,提出了一种天线波束指向分析模型。首先,利用计算流体力学方法对天线表面的风压分布情况进行了数值模拟,得到了天线表面的风压系数。然后,利用风压系数与风速无关的特性,分析了不同风速工况下天线结构变形的规律。最后,根据天线结构变形的特点,分析了天线在不同工作状态下的增益损失、指向偏差等的变化规律。结果表明,所提出的模型可以快速评估大口径反射面天线在风载荷下的变形情况和波束指向特性,这为后续的天线抗风结构设计与系统控制研究提供了理论指导。

VICTS天线的波束指向误差补偿方法

针对可变倾角连续断面节阵列(Variable Inclination Continuous Transverse Stub,VICTS)天线的波束指向误差问题,提出了一种补偿方法。首先介绍了VICTS天线的基本原理和组成,建立了波束指向模型。然后分析了误差来源,包括结构误差、馈源层及辐射枝节层的角度关系等因素,通过仿真得出了波束指向角与馈源层和辐射枝节层夹角的关系。在此基础上,提出了通过二次曲线拟合进行误差补偿的方法,并进行了对星试验。实验结果表明,该方法能够有效减小波束指向误差,提高通信系统的性能,具有较高的实用性。

太阳同步对日定向卫星的测控天线布局设计

对日定向姿态卫星在轨没有固定指向地球的一侧,若采用在卫星对天面和对地面反向对称各安装一副测控天线以实现准全向覆盖的传统布局设计,在测控弧段中地面站方位跨越测控天线组合方向图干涉区的过程中,测控链路极易受到该区域天线增益的剧烈波动而出现链路中断,从而对测控任务产生较大影响。太阳同步轨道具有轨道平面和太阳矢量保持相对固定夹角的特性,若运行于太阳同步轨道的卫星采用对日定向姿态,则可利用该轨道特性,结合我国地面站主要位于北半球的特点,通过优化测控天线在星上的布局,减少测控天线干涉区对测控链路的影响。通过仿真分析给出该设计的具体实现过程,并给出不同轨道高度和降交点地方时对应的测控天线推荐安装角度,可为运行在太阳同步轨道上的对日定向姿态卫星提供测控天线布局参考。

基于MATLAB的天伺馈模态分析

依据天线指向计算、伺服控制等算法,通过MATLAB分别建立天线指向计算中自主推算、直接注入模型、伺服控制中计算速度控制量模型及天线运动方式三种算法验证模型,并对各模型理论模态和实际样例数据进行模态分析。分析结果表示,基于MATLAB建立的天线伺服模型是正确的,天线运动趋势验证方法是可行的。此模型推算结果可有效对算法算例进行佐证,模态分析提供了大量的运动样本数据及相应参数下的天线运动趋势,不仅有利于测试人员更快掌握天线伺服算法理论知识,还能为雷达天线座及伺服系统动态研究提供理论支持。

无人机机载测控天线自动选择算法

中大型无人机通常配备多幅天线来降低机体遮挡和空域覆盖不够的影响,传统地面测控站手动选择天线的方式存在准确性不高、时效性差、占用操控员精力等缺点。分析了先进无人机测控链路架构,提出基于无源天线方向图的自动天线选择算法,通过实测或仿真天线增益数据形成拟合曲线,根据地面站投影在飞机坐标系下的方位俯仰实现自适应天线选择。针对有源相控阵或定向天线,提出机体坐标系到相控阵天线坐标系的转换矩阵和波束指向算法。给出测控直扩波形信噪比计算方法,将信号质量算法作为卫星导航失效情况下自动天线选择的备份手段。所提算法在准确性、时效性和自动化水平上相对传统手动方式有较大提升,飞行试验数据表明本文算法有效支撑无人机与测控站的稳定可靠通信。

不同测地型GNSS接收机在峡谷区控制测量数据分析

某水库勘测设计阶段测图控制网采用四等GNSS三维控制网(精化高程),针对测区山大沟深,地形陡峻,属于典型的“V”型高山峡谷地形,可见卫星数量很少,且高度角大于30°,控制网测量时分别采用8套华测i90接收机和8套华测P5(配套HXCCGX601A扼流圈天线)接收机,对两种接收机的观测数据、基线精度、同步环闭合差、平差精度等方面进行对比分析,数据比较结果表明,带有扼流圈天线的分体型GNSS接收机在高山峡谷条件下观测效果强于标称精度相同的一体化GNSS接收机,建议在类似不利观测条件下应尽量选择带扼流圈天线的分体型GNSS接收机。

一种基于无人机的口面天线外场测试方法

口面天线辐射场的功率分布是天线应用中应仔细考虑的关键因素,应用无人机在空中对天线辐射功率的分布进行测量是一种较便捷和准确的方法。论文首先研究了口面天线辐射功率的分布,提出一种应用无人机测试的采样点网,研究了无人机在测试域中的坐标转换,使用Matlab对基于采样点网数据重构的辐射场分布进行了仿真验证,结果表明方法可行有效。最后对该方法的改进方向作了研究展望。

星载天线双轴定位机构指向精度分析

以星载天线双轴定位机构为对象,分析了其指向精度的影响因素,从传动误差、测量误差、安装误差以及热变形误差等方面,研究了各项精度影响因素的分析模型和计算方法,建立了指向精度的分析模型,并以某一天线双轴定位机构为例进行指向精度分析。

星载天线指向精度建模与分析

随着天线定位机构运动日趋复杂以及对定位机构任务要求的不断提高,提高指向精度已成为星载天线机构能力提升的核心。综合考虑卫星姿态控制误差、展开机构误差、双轴驱动机构误差和反射面误差等因素,利用齐次变换矩阵得到天线指向运动学误差等式,从而得到天线指向精度分析的一般方法。以某星载点波束定位机构为例,对各误差源的影响进行了分析,得到双轴驱动机构任意转角位置下各误差源对最终指向精度的影响,分析结果表明:姿态控制误差、展开机构锁定误差对精度的影响不容忽视,需要综合考虑各部分误差因素,才能从根本上提高天线的指向精度。

天线指向机构位置伺服的H_∞-PID控制研究

针对大型卫星天线指向机构高精度高可靠性的要求,研制了一种永磁同步电机驱动的新型天线指向机构。在建立双质量体驱动模型的基础上,以ITAE(时间乘以误差绝对值积分)为优化指标,在H∞混合灵敏度约束下PID参数的稳定域内,采用遗传算法对PID控制器的参数进行了优化。最后采用优化的PID控制器对指向机构进行了控制仿真和实验验证,结果表明系统具有响应快速而平稳、抗负载扰动和模型误差能力强的特点。