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101.
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The envelope of a hypersonic vehicle is affected by severe fluctuating pressure, which causes the airborne antenna to vibrate slightly. This vibration mixes with the transmitted signals and thus introduces additional multiplicative phase noise. Antenna vibration and signal coupling effects as well as their influence on the lock threshold of the hypersonic vehicle carrier tracking system of the Ka band are investigated in this study. A vibration model is initially established to obtain phase noise in consideration of the inherent relationship between vibration displacement and electromagnetic wavelength. An analytical model of the Phase-Locked Loop(PLL), which is widely used in carrier tracking systems, is established. The coupling effects on carrier tracking performance are investigated and quantitatively analyzed by imposing the multiplicative phase noise on the PLL model. Simulation results show that the phase noise presents a Gaussian distribution and is similar to vibration displacement variation. A large standard deviation in vibration displacement exerts a significant effect on the lock threshold. A critical standard deviation is observed in the PLL of Binary Phase Shift Keying(BPSK) and Quadrature Phase Shift Keying(QPSK) signals. The effect on QPSK signals is more severe than that on BPSK signals. The maximum tolerable standard deviations normalized by the wavelength of the carrier are 0.04 and 0.02 for BPSK and QPSK signals,respectively. With these critical standard deviations, lock thresholds are increased from à12 andà4 d B to 3 and à2 d B, respectively. 相似文献
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105.
空间机械的润滑不同于地面设备,星载天线指向机构更有其本身的特点,应针对天线指向机构不同组件的工作特点选择最适合的润滑方式。文章对目前空间机械常用的几种润滑方式的机理和优缺点进行了综述,指出了天线指向机构润滑设计应考虑的问题和不同组件可采取的润滑措施。 相似文献
106.
天线视角是航天测量船的一个重要指标,通过分析各种视角遮挡情况,列出相应的视角计算方法,为船用天线视角设计提供了依据。同时本文分析了针对视角遮挡问题在船舶设计阶段应采取的措施。 相似文献
107.
设计了一种柔性减速刷消旋机构,将其安装于七自由度机械臂的末端,通过与翻滚目标帆板之间的接触碰撞进行消旋。利用绝对节点坐标法推导了柔性减速刷的动力学模型,并对其接触碰撞进行分析。针对自由漂浮空间机器人动力学建模和基座姿态的控制进行了研究,采用基于计算力矩法的滑模控制策略,对末端参数不确定的七自由度机械臂进行控制。滑模控制具有快速响应、对参数变化及扰动不灵敏等特点,确保了系统的全局鲁棒性和稳定性。有利于节省消旋时间,提高消旋效率。通过PD控制和滑模控制消旋仿真验证,该消旋策略能够成功消除初始旋转速度,消旋程度达90%以上,具有可行性与有效性。 相似文献
108.
W. Singer R. Latteck D.A. Holdsworth 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(9):1488-1494
A Doppler radar at 3.17 MHz has been installed at Saura close to the Andøya Rocket Range as part of the ALOMAR observatory at Andenes, Norway in summer 2002 to improve the ground based capabilities for measurements of small scale features and turbulence in the mesosphere. The main feature of the new Saura MF radar is the transmitting/receiving antenna which is arranged as a Mills Cross of 29 crossed half-wave dipoles with a minimum beam width of about 7°. Each dipole is fed by its own transceiver, and the individual phase control of the 58 transceiver modules on transmission and reception provides high flexibility in beam forming and pointing as well as transmission switching between ordinary and extraordinary mode circular polarisation. In addition, beams with different widths at the same pointing angle can be formed. For multiple receiver applications (spaced antenna wind measurements, all-sky meteor detections) four independent receiving channels are available. 相似文献
109.
星载 ScanSAR 特性研究 总被引:2,自引:0,他引:2
袁孝康 《中国空间科学技术》1998,18(4):43-50
论述了星载波束扫描合成孔径雷达(ScanSAR)的扫描覆盖特性,指出在满足观测带远端模糊性约束条件下,最大观测带宽度与雷达波长和实际天线孔径的形状无关;阐述了观测带宽度与雷达分辨率、天线面积、发射功率和回波数据率等参数之间的约束关系;给出了数值计算例子。 相似文献
110.
论述了VLBI25m天线电参数测试系统,着重介绍了自行研制的同轴液氮冷热噪声源,并进行了可行性和误差分析,其精度可以达到国家二极标准,同轴接口误差为±1.0K,满足了VLBI的实际应用。 相似文献