在卫星授时中电离层误差实时改正的双极化方法

在卫星定位与授时中，电离层折射误差的影响是十分重要的．目前采用的主要改正方法是双频法，还有电离层模型法．双频法要求卫星发射两个工作频率，而电离层模型法的偏差又较大，这对于使用单频接收机的用户来讲，电离层折射改正就成为一个严重问题，笔者提出的双极化法正好可以解决单频接收机所遇到的问题．双极化法是基于电离层的双折射特性．一个线极化波在电离层中传播时被分裂成两个圆极化波，即左旋圆极化波和右旋圆极化波传播，左旋与右旋圆极化波在电离层中传播的速度不同，则到达接收点的时间也就不同，通过测量两个圆极化波到达接收点的传播时廷差，即可确定电离层折射误差的改正量．     

K波段宽带圆极化器设计

设计了一个K波段圆极化器,其工作频率为18至26.5 GHz。K波段包含多条重要的射电天文分子谱线,此波段圆极化器的研制对于天文观测与科学研究有极其重要的意义。圆极化器用于将线极化波转换为圆极化波以便于射电望远镜进行观测。包括其工作原理、设计要点、模型仿真结果等内容。主要着眼于正交模式转换器与移相器这两个圆极化器中的重要器件,通过工作原理分析以及电磁仿真的方法进行器件的具体设计并得出仿真结果。仿真结果各个端口回波损耗均小于-20 d B,且移相器的移相误差小于3.3°。     

Q波段宽带圆极化器设计与研究

为满足天马望远镜Q波段(35-50 GHz)双波束致冷接收机的需求,介绍了一种Q波段宽带圆极化器的设计。圆极化器采用90°移相器与正交模式转换器组合的方式,其中,90°移相器利用双壁波纹移相结构,仿真结果表明,工作带宽内可以达到90°±3°;正交模式转换器采用十字转门结构,仿真结果表明各端口反射系数好于-25 dB,输出端口隔离度好于-60 dB。文章还给出了对实际加工90°移相器与正交模式转换器具有指导意义的容差分析,并且给出了90°移相器与正交模式转换器组合的仿真结果。组合而成的圆极化器性能满足天马望远镜Q波段致冷接收机的设计指标:端口反射系数好于-20 dB,输出端口隔离度好于-32 dB。     

CSRH光传输线的长度及相位测量

简述CSRH等长光传输线的物理意义,实现等长光传输线的几种方法,通过分析确定了光纤等长精度要求。介绍了两种测量光纤长度的方法,分析计算了CSRH光传输线的相位误差,最后描述了光传输线的相位检测方法。     

天马望远镜Ka波段宽带圆极化器研制

天马望远镜Ka波段宽带接收机是研究恒星形成、星际介质以及深空探测的重要观测平台。论述了接收机核心器件Ka波段宽带圆极化器的研制过程。该器件由90°两壁波纹移相器和改进型双脊波导形式的正交模式耦合器构成,工作频带为26.5~40 GHz,相对带宽达到41%。首先介绍了圆极化器的应用背景及工作原理,继而进行模型设计和仿真优化,最后进行结构设计和样品实测。实测结果显示,移相器的相移误差为90±4°,轴比达到0.6 d B,正交模式耦合器的交叉极化为-26 d B,隔离度为-35 d B,器件端口驻波均低于-18 d B,实测结果与设计仿真相符。     

一种基于相位条纹的高精度码相位测量方法

全球导航卫星系统(Global Navigation Satellite System,GNSS)接收机在接收卫星信号后,经过捕获、跟踪,得到码相位与载波相位两个基本测量值,然后通过测量值计算卫星与接收机之间的距离.载波相位测量值比码相位测量值具有更高的测量精度,但由于载波相位测量值具有计算整周模糊度的问题,得到高精度...     

新疆天文台26米望远镜L波段接收机线-圆偏振的转换

新疆天文台南山基地26 m射电望远镜L波段接收机使用线偏振馈源接收电磁波信号用于脉冲星观测。分子谱线观测和VLBI国际联测需要圆偏振信号,因此希望接收机能够观测圆偏振信号。论述了将线偏振电磁波转换为圆偏振电磁波的方案,研究了90 °电桥在偏振转换中的作用,介绍了偏振转换的调试方法。在圆偏振模块中使用90 °电桥完成线偏振信号到圆偏振信号的转换,两路圆偏振信号的隔离度达到使用要求,满足圆偏振观测的需求。这种线偏振信号到圆偏振信号的转换方式不影响接收机的系统温度。     

静态测量型GPS接收机的研制及其性能

静态测量型GPS接收机系统由8通道、单频ST-1接收机和静态后处理软件两部分组成,通过跟踪测量卫星载波信号、测距码信号及数据码(包含有星历数据)信号,获得伪距和载波相位观测值,采用差分(主要是双差)处理方法,达到精确测定两接收机天线间相对位置的目的.基线测量精度为10mm+2ppm×D.     

GPS接收机天线相位中心偏差的检测

GPS接收机天线相位中心偏差是指GPS天线接收卫星信号的电气中心与基机械几何中心之差。在高精度测量中，这是不容忽视的。讨论了采用基线测量相对测定法确定天线相位中心在水平和垂直方向上的偏差的原理和方法，并给出了测量结果及建议。     

全息测量接收机系统

简单介绍了微波全息测量的原理、用于微波全息测量的接收机系统,然后比较详细地叙述了对该接收机系统相位稳定性的测试,指出了当前接收系统的主要问题。并对接收系统的改进做了两种设计方案。     

候选射电脉冲星的预测

对已知脉冲星大样本的统计和分析表明,绝大多数脉冲星的线偏振大于１０％,谱指数低于－１．比较了脉冲星和射电类星体及致密陡谱源的频谱和偏振特性的差别,以高线偏振、高谱指数、高银纬及在低频下较低流量等作为射电脉冲星候选者的判据,从新近释放的ＶＬＡ巡天和ＷＳＲＴ巡天结果中挑选出一个较粗的候选脉冲星样本．进一步考虑近期在部分天区中已作过高灵敏度的脉冲星巡天,所有落入这些天区内的候选源也都从本样本中排出．以候选源偏振度大小为序,给出了一个共４７颗候选源的子样本．     

致密射电源的快速偏振变化和星际闪烁模型

以类星体０９１７＋６２４中１９８９年５月观测到的ＩＤＶ事件为实例,尝试提出一个４成分模型（１个稳定成分和 ３个闪烁成分）以充分解释在 ６ ｃｍ波长上观测到的偏振变化,包括流量和偏振流量的相关性和反相关性以及它们之间的快速转化．对于 ２０ ｃｍ波长上观测到的偏振变化,３成分模型（１个稳定成分和３个闪烁成分）已足以解释全部现象．文中提出的闪烁模型在解释ＩＤＶ事件的偏振变化方面改进了以前的模型拟合．     

Circular Polarization in Pulsar Integrated Profiles： Updates

We update the systematic studies of circular polarization in integrated pulse profiles by Han et al. Data of circular polarization profiles are compiled. Sense reversals can occur in core or cone components, or near the intersection between components. The correlation between the sense of circular polarization and the sense of position angle variation for conal-double pulsars is confirmed with a much large database. Circular polarization of some pulsars has clear changes with frequency. Circular polarization of millisecond pulsars is marginally different from that of normal pulsars.     

Theoretical Models for Producing Circularly Polarized Radiation in Extragalactic Radio Sources

We discuss the production of circular polarization in compact radio sources both by the intrinsic mechanism and by Faraday conversion. We pay particular attention to the magnetic field structure, considering partially ordered fields and Laing sheets, and distinguishing between uniform and unidirectional fields. (The latter can be constrained by flux conservation arguments.) In most cases, Faraday conversion is the more important mechanism. Conversion operates on Stokes U, which can be generated by internal Faraday rotation, or by magnetic field fluctuations, which can therefore produce circular polarization even in a pure pair plasma. We also show that the spectrum of circular polarization in an inhomogeneous jet can be quite different from that in a uniform source, being flat or even inverted.     

Milestones in the Observations of Cosmic Magnetic Fields

Magnetic fields are observed everywhere in the universe. In this review, we concentrate on the observational aspects of the magnetic fields of Galactic and extragalactic objects. Readers can follow the milestones in the observations of cosmic magnetic fields obtained from the most important tracers of magnetic fields, namely, the star-light polarization, the Zeeman effect, the rotation measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio polarization observations, as well as the newly implemented sub-mm and mm polarization capabilities. The magnetic field of the Galaxy was first discovered in 1949 by optical polarization observations. The local magnetic fields within one or two kpc have been well delineated by starlight polarization data. The polarization observations of diffuse Galactic radio background emission in 1962 confirmed unequivocally the existence of a Galactic magnetic field. The bulk of the present information about the magnetic fields in the Galaxy comes from anal     

Multifrequency Polarization Variations in the Quasar 0917＋624

We present a detailed analysis of multi-frequency observations of linear polarization in the intraday variable quasar 0917+624 (z = 1.44). The observations were made in May 1989 at five frequencies (1.4, 2.7, 5.0, 8.3 and 15GHz) with the VLA and the Effelsberg 100 m-telescope and in December 1988 at two frequencies (2.7 and 5.0 GHz) with the latter. It is shown that the relationship between the variations of the polarized and total flux density is highly wavelength dependent, and the multi-frequency polarization behavior may be essential for investigating the mechanisms causing these variations. It is shown that the variations observed at 20 cm can be interpreted in terms of refractive interstellar scintillation. However, after subtracting the variation due to scintillation, three 'features' emerged in the light-curve of the polarized flux density, indicating an additional variable component. Interestingly, these features are shown to be correlated with the variations at 2-6 cm, thus indicating that thes     

Polarization Position Angle Swings caused by Relativistic Effects

Polarization position angle swings of - 180 ° observed in extragalactic radio sources are a regular behavior of variability in polarization. They should be due to some kind of physically regular process. We consider relativistic shocks which propagate through and 'illuminate' regular configurations of magnetic field, producing polarization angle swing events. Two magnetic field configurations (force-free field and homogeneous helical field) are considered to demonstrate the results. It is shown that the properties of polarization angle swings and the relationship between the swings and variations in total and polarized flux density are critically dependent on the configuration of magnetic field and the dynamical behavior of the shock. In particular, we find that in some cases polarization angle swings can occur when the total and polarized flux densities only vary by a very small amount. These results may be useful for understanding the polarization variability with both long and short timescales obser     

Ha Line Polarization in the 2B/X4.8 Flare of 2002 July 23

On 2002 July 23, a 2B/X4.8 flare was observed in the Ha line spec-tropolarimetrically by the Large Solar Vacuum Telescope of Baikal Astrophysical Observatory. Linear polarization of 3%-10% was detected in the Ha line, particularly where the line showed central reversal. The linear polarization is mainly radial on the solar disk and appears at the impulsive phase of the hard X-ray and 7-ray bursts. It is limited to some relatively small regions of the flare. The polarization in a limited small region (~ 4" - 5") changed its direction within a short period of time (~ 10s).     

An Electron Density Model above the Sunspot from a Mapping of NOAA 7260 at 17 GHz

The brightness temperature distribution of microwave emission in a solar active region generally shows a ring structure, with a dip at the centre. However, no dip was found in the Nobeyama Radioheliograph left handed circular polarization (LCP) image on 1992 August 18; instead, there was a peak. This is a completely LCP source with zero right-handed circular polarization (RCP). We examine this structure in terms of the joint effect of gyroresonance and bremsstrahlung mechanism with a raised electron density above the central part of the sunspot, and the commonly assumed temperature and vertical dipole magnetic field models. The raised electron density is found to be 1.4 × 1011 cm-3 at the chromosphere base.     

Polarization Calibration of the Solar Optical Telescope onboard Hinode

The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector magnetic fields on the Sun through precise spectropolarimetry of solar spectral lines with a spatial resolution of 0.2 – 0.3 arcsec. A photometric accuracy of 10⁻³ is achieved and, after the polarization calibration, any artificial polarization from crosstalk among Stokes parameters is required to be suppressed below the level of the statistical noise over the SOT’s field of view. This goal was achieved by the highly optimized design of the SOT as a polarimeter, extensive analyses and testing of optical elements, and an end-to-end calibration test of the entire system. In this paper we review both the approach adopted to realize the high-precision polarimeter of the SOT and its final polarization characteristics.