Ku波段低噪声放大器的设计

设计一款Ku波段低噪声放大器,放大器采用两级PHEMT晶体管(VMMK1225)级联结构,单电源供电模式。应用微波仿真软件ADS对匹配电路进行优化设计,在11.7GHz～12.5GHz的工作频段内放大器噪声系数小于0.23 dB,带内增益大于31dB,输入、输出驻波比小于1.6。仿真结果表明,设计完全满足性能指标要求。     

微波移频传输系统的分析设计

在视距传播、系统噪声等方面对射频无线转发系统进分析和设计，，采取利用地形避免干涉型衰落、进行合理的系统电平分配和控制信道幅频特性等措施，较好地保证了系统性能。     

微机电陀螺解调过程中的噪声传递机理研究

微机电陀螺的噪声性能是衡量陀螺综合性能的重要指标之一,不仅与陀螺本身机械结构有关,还与其测控电路有着密切联系。本文将通过理论推导计算出噪声经过乘法解调和开关解调时的传递机理,指出开关解调会使解调信号中的谐波成分和解调输入噪声向解调后的基带中进行混叠,相对于纯正弦解调会增大噪声,最后应用LabVIEW软件进行纯软件仿真和半实物仿真验证,并通过实际测试数据证明其正确性,为陀螺解调方案的选择提供依据。     

Effects on noise properties of GPS time series caused by higher-order ionospheric corrections

Higher-order ionospheric (HOI) effects are one of the principal technique-specific error sources in precise global positioning system (GPS) analysis. These effects also influence the non-linear characteristics of GPS coordinate time series. In this paper, we investigate these effects on coordinate time series in terms of seasonal variations and noise amplitudes. Both power spectral techniques and maximum likelihood estimators (MLE) are used to evaluate these effects quantitatively and qualitatively. Our results show an overall improvement for the analysis of global sites if HOI effects are considered. We note that the noise spectral index that is used for the determination of the optimal noise models in our analysis ranged between −1 and 0 both with and without HOI corrections, implying that the coloured noise cannot be removed by these corrections. However, the corrections were found to have improved noise properties for global sites. After the corrections were applied, the noise amplitudes at most sites decreased, among which the white noise amplitudes decreased remarkably. The white noise amplitudes of up to 81.8% of the selected sites decreased in the up component, and the flicker noise of 67.5% of the sites decreased in the north component. Stacked periodogram results show that, no matter whether the HOI effects are considered or not, a common fundamental period of 1.04 cycles per year (cpy), together with the expected annual and semi-annual signals, can explain all peaks of the north and up components well. For the east component, however, reasonable results can be obtained only based on HOI corrections. HOI corrections are useful for better detecting the periodic signals in GPS coordinate time series. Moreover, the corrections contributed partly to the seasonal variations of the selected sites, especially for the up component. Statistically, HOI corrections reduced more than 50% and more than 65% of the annual and semi-annual amplitudes respectively at the selected sites.     

A noise attenuation method for medium-energy electron measurements in the radiation belt

From the viewpoint of plasma particle measurements in the radiation belt, background noise is a serious problem. High-energy particles penetrating the sensor shielding generate spurious signals, and their count rate often can be comparable to the true signals. In order to attenuate such background noise during medium-energy (5–83 keV) electron measurements, we propose the double energy analyses (DEA) method. DEA is conducted by a combination of an electrostatic analyser (ESA) and avalanche photo-diodes (APDs); ESA and APD independently determine the energy of each incoming particle. By using the DEA method, therefore, the penetrating particles can be rejected when the two energy determinations are inconsistent; spurious noise are caused only when the deposited energy at an APD is by chance consistent with the measured energy by ESA. We formulate the noise count rate and show the advantage of DEA method quantitatively.     

基于样条逼近的周期性测量误差检测方法

对周期信号进行多个节点距的等距三次样条拟合，研究其残差能量谱，总结出等距样条节点距变化与残差中周期性频率出现的规律。运用时域抽样理论对该现象加以研究，给出理论证明。在此基础上，结合工程实践中外测数据的误差特性，将传统的周期性误差检测方法加以延伸，提出了基于样条逼近的周期性测量误差检测方法。仿真结果表明，新方法对于提高外测数据中周期项的提取能力效果明显。     

25m天线电参数测试系统

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。     

一种实用的边缘强度互相关匹配可信度分析方法

匹配可信度是衡量匹配质量的重要指标，针对归一化边缘强度互相关匹配算法，研究了基于神经网络的匹配可信度判别方法。通过对参考图进行加噪实验获得训练样本，对BP网络进行训练，并将训练后的网络用于匹配可信度的判别。针对实际卫片与航片图像对的实验结果，平均判决正确率达到90％以上，证实了该方法的有效性。     

固体发动机静止试验噪声分析的新途径

喷流噪声和气动噪声引起的声振是固体发动机静止试验时最严重的振环境。噪声分析通常是用精密声级计和滤波器，倍频程谱分析需用１１个档位的滤波器，１／３倍频程则需用３４个档位的滤波器。