用射电天文方法测量天线参数

本文介绍了以月亮为校准源,以液氮低温负载与常温负载为定标基准,利用开关型辐射计,进行天线参数测量的基本原理和方法。被测天线口径为5米,工作波长为7.5厘米,馈源采用石家庄通信研究所研制的复合式多模喇叭。测量结果表明,用射电天文方法测量天线参数可得到满意结果,既精确又方便。此法还能方便地测出用经典方法不能测试的天线噪声温度。     

微波天线增益的高精度测量

本文介绍一种以冷空背景为定标基准,测量系统和接收系统兼容的测量设备实现微波天线增益高精度测量的方法。该方法对测量天线——接收机系统的天线增益尤为方便,它的测量精度高,不受频率限制。测量结果表明该方法有广泛的实用前景。     

遥感微波辐射计逆向辐射噪声对天线温度标定的影响

本文分析了遥感微波辐射计的逆向辐射噪声温度和口面定标源的亮度温度，建立了口面定标源的亮度温度模型。深入分析用口面定标方法反演微波辐射计的天线温度时过向辐射噪声对天线温度标定的影响。     

以月亮为校准源测量天线参数

本文介绍了以月亮为校准源,液氮低温负载为定标基准,进行天线参数测量的原理和方法;并给出利用2米口径的3.2厘米波射电望远镜进行实测的具体方案和结果。测量结果表明:这种方法简便、精确、可靠,它可使用于中、小型天线的参数测量。     

低旁瓣微波辐射计天线设计和应用

提出一种高灵敏度微波辐射计设计方法,它采用辐射计天线的低旁瓣和高主波束效率设计,通过降低辐射计的系统噪声温度(尤其是外部变化的天线噪声温度),实现系统的高灵敏度。给出了微波辐射计天线方向图的理论仿真和实验结果及系统灵敏度的测量结果。辐射计天线实测结果表明:二个波段的天线副瓣电平均低达-30dB,天线主波束效率均高于95%。微波辐射计系统的实测结果表明:新方法使辐射计实际测量达到0.05K的高灵敏度。该系统也可在大气遥感测量、人工影响天气、土壤水分测量等领域应用,为防洪抗旱提供实时的降雨特性资料,在雷达和卫星通讯等领域,应用于电波的中性大气折射订正。     

卫星地面接收天线系统噪声温度的测量

在广播卫星系统中,接收天线增益与接收机输入端总的噪声温度之比称为接收装置的品质因素,它是评价接收装置质量的一个重要参数。而其质量的好坏最终决定于天线装置和接收机的总噪声温度。下面讨论用实验确定[屏幕]系统地面接收站接收天线装置的噪声温度的方法和实测结果。计算方法。根据文献〔4〕,接收机输入     

基于定标体散射特性的天线极化特性的测量

天线的极化特性是描述天线性能的重要参数,是雷达目标特性测量领域的基础性问题,对于实际的雷达天线而言,其极化特性的外场测量是一项复杂而又艰巨的工作。文章提出了一种基于定标体散射特性的天线极化特性的测量处理方法,建立了雷达波束扫描定标体的接收回波模型,可实现对线极化和圆极化天线极化特性的测量,给出了外场实验布局和测量步骤,实测数据和仿真实验证明了该方法的可行性。该方法能够有效地减少设备量和降低测量成本,提高雷达远场的逼真度。     

有源阵列天线的噪声温度

有源阵列天线系统的噪声是有源相控阵雷达系统噪声的主要成分,通过建立基于有源阵列天线系统的噪声分析模型,给出该系统噪声温度的具体计算方法,得到该系统噪声温度的计算公式,进一步推导出该系统增益与噪声温度比值的计算和测试方法.并通过实际计算分析,验证了该方法的有效性.     

一种星载SAR定标接收机误差分析

作为星载SAR地面微波辐射定标场主要外定标设备,定标接收机用于完成星载SAR天线方向图和辐射功率的测量。为实现高精度测量,需要定标接收机有很高的测量精度。本文对定标接收机的高精度指标进行了定量误差分析,介绍了定标接收机的工作原理,给出了误差计算模型和误差分析方法。该方法利用误差精度分配及误差计算最大值来分析定标接收机的精度指标,并给出了定标接收机各项精度指标的实测结果,验证了该误差分析方法的正确性和精确性。     

日凌时天线噪声温度分析

在提出日凌干扰处理新模型的基础上，系统阐述了日凌时天线噪声温度的分析方法，把足以影响日凌干扰整个变化过程的特征量－－天线噪声温度增量作为分析与研究的中心，从总体上把握日凌干扰过程，提出了日凌中心日期中心时刻的天线噪声温度，以及整个日凌过程中各日期各时刻的天线噪声温度增量变化的理论计算模型。     

手动VSAT站天线接收增益的诊断测量

阐述了利用卫星信标和高增益标准喇叭天线,测量手动VSAT站天线接收增益的方法。由测量的天线接收增益计算天线接收效率,从而实现对天线发射增益进行估算。最后,给出了工程测量实例,证明了该方法的可行性,并对增益测量误差进行了分析,其均方根误差±0.28dB。     

微航姿仪的磁力计标定算法及误差补偿研究

针对目前磁力计标定算法中存在磁干扰或噪声导致航向角测量误差等问题,提出了一种改进的磁力计标定算法。该算法考虑磁力计安装误差和外界磁干扰,提出改进的磁力计误差模型;同时运用BP神经网络训练软磁干扰下的磁航向与真实航向之间的非线性关系,降低了非线性误差。通过仿真和实验验证,算法有效地解决了磁力计误差补偿问题,降低了软硬磁干扰对航向角的影响,得到较精确的航向角,误差范围在±1°内,证明了改进误差补偿算法的可行性和有效性。     

Kinematic calibration of a 3-P(Pa)S parallel-type spindle head considering the thermal error

Calibration is considered to be the most effective way to improve the accuracy of parallel kinematic machine tools (PKMTs). However, ordinary calibrations only considered the time-invariant errors (manufacturing error), neglecting some time-variant errors, a significant one of which is thermal error. Therefore, in this paper, the influence of thermal error was considered in the calibration of a 3-P(Pa)S parallel-type spindle head. First, a new kinematic model of the spindle head was proposed, which is closer to the real physical model, so the thermal error of the spindle head can be considered in the model. Second, the structural parameters of the spindle head were expressed as the sum of the ideal parameters, the manufacturing errors, and the thermal errors. Third, the pose (position and orientation) of the end effector and the temperature of the spindle head were measured. The positions of the temperature sensors were selected using the global temperature sensitivity index (GTSI), which is derived from the global sensitivity index (GSI). Thus, by setting a standard temperature, the thermal error of the structural parameter can be obtained. Fourth, the influence of the thermal error was inputted into the identification equation for calibration, so the results are the structural parameters at the standard temperature (20 °C). To solve the ill-conditioning problem, a Regularization method was used in the identification. Finally, the calibration was verified on a 3-P(Pa)S-XY machine tool. The RTCP test, performed immediately after the measurement, shows that the maximum position error after the calibration is 0.019 mm at the tilt angle of 30° and 0.037 mm at 20°. In addition, the RTCP test after a temperature change shows that the calibration considering the thermal error can improve the average position accuracy from 0.025 mm to 0.015 mm. The calibration method in this paper is expected to be applicable for other machine tools.     

阵列天线因随机振动引起的测向误差分析及校准

针对阵列天线受舰船甲板低频机械随机振动引发振子位移变化导致的测向误差问题,建立了天线振子随机振动误差模型,仿真分析了天线阵列3个轴向随机振动模式对测角接收信号的影响,提出了一种基于多个接收机在不同位置同时测量的测角误差校正方法.该方法采用最小二乘法得到多个误差校准矢量,通过调用天线波束指向扇区内校准矢量的方法进行误差补偿,解决了低频随机振动模式下阵列天线测角误差的校准问题.该方法已应用到舰载微波着舰引导系统数据解算中.     

GEO SAR天线波束指向定标中的误差分析

GEO SAR因其超宽测绘带和超长的合成孔径时间,导致低轨SAR波束指向定标方法不再适用,进而采取基于多脉冲分时比幅的波束指向定标方法。本文针对该指向定标方法,结合GEO SAR星地几何关系,对卫星姿态变化、三维系统性误差以及波束指向定标方法中接收机信噪比和通道增益稳定性引入的指向误差进行了详细的推导和仿真分析。仿真结果表明,0.003°的姿态测量误差会引入0.003°的距离向指向误差和0.0033°的方位向指向误差;三维系统性误差是导致天线波束指向变化的主要误差源;当SNR≥35 dB、通道增益稳定性优于1 dB时,GEO SAR波束指向定标方法引入的指向误差小于0.001°。     

EMI antenna calibration on an absorber-lined ground plane to determine free-space antenna factor

Theoretical and experimental investigations are carried out on the establishment of a quasi-free-space environment for electromagnetic interference antenna calibration using ferrite-tile absorbers at the test site. Numerical techniques are developed to evaluate the accuracy of the free-space antenna factor obtained on the absorbers when the ferrite-tile material constants are known. In addition, the antenna impedance measurement on a tuned dipole antenna is proposed for evaluating the calibration error caused by the unwanted ground reflection. Experiments confirm the validity of the numerical techniques and demonstrate that commercially available ferrite tiles can drastically reduce ground reflection even in a lower very-high-frequency (VHF) range. It is concluded that the standard antenna method can yield free-space values of the antenna factor for the entire VHF region with an error of less than 0.3 dB, if ferrite tiles are placed on a metal ground plane greater than 8.7/spl times/8.7 m/sup 2/ and if the antenna under calibration is positioned at a height of about 3 m.     

Analysis and improvement of tipping calibration for ground-basedmicrowave radiometers

The tipping-curve calibration method has been an important calibration technique for ground-based microwave radiometers that measure atmospheric emission at low optical depth. The method calibrates a radiometer system using data taken by the radiometer at two or more viewing angles in the atmosphere. In this method, the relationship between atmospheric opacity and viewing angle is used as a constraint for deriving the system calibration response. Because this method couples the system with radiative transfer theory and atmospheric conditions, evaluations of its performance have been difficult. In this paper, first a data-simulation approach is taken to isolate and analyze those influential factors in the calibration process and effective techniques are developed to reduce calibration uncertainties. Then, these techniques are applied to experimental data. The influential factors include radiometer antenna beam width, radiometer pointing error, mean radiating temperature error, and horizontal inhomogeneity in the atmosphere, as well as some other factors of minor importance. It is demonstrated that calibration uncertainties from these error sources can be large and unacceptable. Fortunately, it was found that by using the techniques reported, the calibration uncertainties can be largely reduced or avoided. With the suggested corrections, the tipping calibration method can provide absolute accuracy of about or better than 0.5 K     

Microwave Thermal Noise Standards

Calibrated microwave thermal noise standards usually consist of a matched resistive element thermally isolated by a transmission line. They are used for microwave radiometry, antenna temperature calibrations, loss measurements, low-noise amplifier performance evaluation, and low-level CW signal level calibrations. The formula used to account for the distributed loss and temperature along the transmission line is derived and simplifying approximations and limitations are noted. Exact (hf/kT<<1) and approximate (hf/kT<<1, /spl pound/<<1) solutions for various loss and temperature distributions are tabulated. A FORTRAN computer program is available for a general solution that uses the transmission-line temperature and loss distributions for input data. The single largest source of calibration error is usually the microwave insertion loss measurements. The construction, calibration, and errors are discussed for a field-operational liquid-nitrogen-cooled waveguide noise standard. This standard is precisely calibrated and has a nominal noise temperature of (78.09 /spl plusmn/ 0.12 peak)/spl deg/K.     

天线立体方向性图的测量

本文叙述了以太阳为信标,用射电天文法测量天线立体方向性图的基本原理和方法。该测量方法用总功率辐射计作为接收系统,用计算机作为终端数据采集和归算系统。它能实时、快速处理,得到天线立体方向性图。被测天线口面直径为20m,波长为17.8cm,可测旁瓣电平约为41dB,精度约为0.6dB。     

电子定标法测试天线罩瞄准误差原理之分析

论述了电子定标法测试天线罩瞄准误差的原理方法,并分析了该方法成立的理由。电子定标法的步骤依次为:收发天线机械轴对准－天线和差通道自检－收发天线电轴对准－电子定标寅无罩测试寅带罩测试－查表计算天线罩瞄准误差。电子定标原理和实测结果表明:测试过程中接收天线差电压与和电压之商,可分解为相对自检过程的共模分量和正交分量;定标过程共模分量保持不变,它决定天线的零深;正交分量随收发天线夹角变化,不受天线零深影响,其曲线为定标曲线;无罩和带罩定标曲线线性度极好,其斜率为天线差斜率;天线加装高性能天线罩后,差斜率变化微小;故可以使用无罩天线差斜率和带罩测试的和差通道电压,计算得出天线罩瞄准误差。差斜率近似引入的误差很小,电子定标法成立。