电子学在天文研究中的一些应用

天文学的研究完全基于对宇宙中天体电脑波辐射的探测和理解，电子学在各种探测过程和信号分析中起着不可或缺的作用。目前国内、国际所有的天文观测设备都必须配备一流的甚至独一无二的电子设备。射电天文学研究天体的无线电波。这里介绍电子在天文研究中的一些应用，特别是射电天文的测量方法，详细介绍探测和研究一种发射脉冲信号的天体（脉冲星）的具体方法。     

射电天文站电磁环境测量方法及分析

射电天文业务是接收来自遥远宇宙天体的射电信号进行研究的科学.由于来自宇宙天体的射电天文信号非常微弱,比通信系统的信号暗弱百万倍,使射电天文望远镜对周围电磁环境的要求极其严格.射电天文站址要选在电磁环境良好的地区,并在以后的运行中得到电磁环境的保护.建立一套测试射电天文站址电磁环境的设备和方法,对射电天文站址的电磁环境进行实际测试,并对实测数据进行科学合理地分析、评价,作为以后射电天文观测和保护电磁环境研究的依据都是非常重要的.     

NLMS算法在射电天文中的应用

射电天文被动接收宇宙中极其微弱的射电信号,很容易受到人们有源业务活动的影响。为了抑制和消除射电望远镜观测过程中出现的电视信号干扰,采取了通常用在通信雷达领域的自适应抗干扰措施,利用两个辅助天线,极大地抑制了电视信号干扰,改善了信噪比,从而能够检测出微弱的射电天文信号。     

Hectometer cosmic static

A review is made of radio astronomy development starting with Jansky at 15-m wavelength and progressing to 30, 60, 144, 576, and 2100 m. Electromagnetic wave propagation through the ionosphere by theO, X, Z, andYmodes including various aberrations is discussed. Methods of overcoming atmospherics are outlined. Preliminary findings at hectometer waves and the cosmological implications are mentioned. The different outlook upon the structure of the universe appears to be a more enticing aspect of the study than details about the contents of the Milky Way. Equipment technology is entirely omitted. A comprehensive list of references to the literature is included, along with four figures.     

Extending the Field of View With Phased Array Techniques: Results of European SKA Research

The radio frequency window of the square kilometre array is planned to cover the wavelength regime from centimeters up to a few meters. For this range to be optimally covered, different antenna concepts are considered. At the lowest frequency range, up to a few gigahertz, it is expected that multibeam techniques will be used, increasing the effective field-of-view to a level that allows very efficient detailed and sensitive exploration of the complete sky. Although sparse narrow-band phased arrays are as old as radio astronomy, multioctave sparse and dense arrays now considered for the SKA require new low-noise design, signal processing, and calibration techniques. The successful implementation of these new array techniques has already been introduced for the use of phased array feeds upgrading existing telescopes: enhancing aperture efficiency as well as effective field-of-view. Especially the development of low-cost array antenna design will allow a cost-effective large-scale implementation for the SKA. This paper addresses these new capabilities, emphasizing the R&D work done in Europe and aims to provide insight into the status of enabling technologies and technical research on polarization, calibration, and side-lobe control that will unleash the potential of phased arrays for future growth of radio astronomy synthesis arrays.     

Gravitational-wave versus electromagnetic-wave antennas

Unlike radio waves, gravitational waves have not yet been conclusively detected. However, there is indirect evidence from the slow decay of binary-pulsar systems. The author describes some of the gravitational antenna hardware, and tries to relate it to the more-familiar antennas of radio, radar, and astronomy. Particularly noted is the phenomenon that an electromagnetic antenna readily intercepts the time-varying wave, whereas a gravitational wave readily passes right through its counterpart, with minuscule energy transfer     

Future trends in antennas and propagation for the US Space Program

The future trends for antennas and propagation in space programs play a prominent role in three areas: information transfer, energy transfer, and remote-vision sensing. Associated with these applications of electromagnetic waves are propagation, scattering, and visualization and simulation. The author shows several unique characteristics, of planetary-surface and interplanetary regions, which have to be considered in developing analytical techniques and hardware. Cost-effective approaches dictate small size, weight, and power consumption, and high reliability. Increased emphasis will be placed on reducing the costs of hardware development, through the innovative use of terrestrial systems which will meet space qualifications. In the terrestrial environment, the ionosphere and atmosphere provide unique interaction with electromagnetic radiation, which must be considered in future applications. In view of the space-program requirements and the unique space environment, the fields of antennas and propagation will find great research challenges. As the limits of exploration of the universe are extended through remote observations, the importance of EM research will increase immensely. This paper explores some trends in this research, based on the anticipated progress in exploration, in device development, and in fabrication, in various parts of the electromagnetic spectrum     

RFI mitigation of GNSS signals for radio astronomy: problems and current techniques

Mitigation of man-made radio frequency interference (RFI) is a problem of increasing importance for radio astronomy. Indeed, numerous terrestrial and satellite services of all kinds create lots of electromagnetic signals in a large part of the radio spectrum that are likely to disturb radio astronomical observations. Moreover, the advent of large, highly sensitive radio telescopes such as SKA, LOFAR, etc., will permit the observation of extremely faint and distant radio sources which exhibit large amounts of red shift, hence overlapping with unprotected bands in the radio spectrum. Among various possible causes of RFI, GNSSs have specific characteristics which can be handled appropriately to design efficient mitigation techniques. GNSS signals are generally well documented and the ephemerides of satellites are well known. Therefore, various partially or fully informed methods can be used, which exploit knowledge of the characteristics of the modulations. Adaptive cancellation techniques can also be used that use auxiliary observations coming from additional antennas. Besides, knowing the spatial direction of the disturbing source, spatial filtering and related techniques that can be implemented in antenna arrays are likely to mitigate RFI with minimum knowledge of the GNSS. After recalling some radio astronomy basics, the paper presents a few examples of RFI caused by satellite systems on radio-astronomical observations. Then, we give a brief overview of state-of-the-art RFI mitigation techniques for radio astronomy and we present in some details the principles and results pertaining to some methods that seem particularly appropriate to mitigate RFI arising from GNSS signals. The importance of cooperation between GNSS designers and astronomers is finally pointed out.     

Radio telescopes

A radio telescope is used in radio astronomy to measure the intensity of the radiation received from various parts of the sky. Such a telescope must be able both to detect and to locate faint radio sources of small angular size, and also to measure the brightness distribution across extended radio sources or over large sky areas. Ideally the telescope should be capable of making such measurements over a wide frequency range and for different types of polarization of the incoming waves. The noise powers available in radio astronomy are very small, and some of the radio sources have angular sizes or angular structure of, perhaps, only one second of arc, so that a radio telescope needs both high gain and good resolving power. The paper describes various types of radio telescopes which have been built and tested, and outlines the astronomical needs which they fulfill. The parabolic reflector antenna is first described, with particular reference to the fully steerable 210-foot telescope at the Australian National Radio Astronomy Observatory and to the 300-foot transit telescope at the U. S. National Radio Astronomy Observatory. Of the telescopes which use fixed or partly fixed reflector surfaces, those at the University of Illinois, at the Nançay station of the Paris Observatory, and at the Arecibo Ionospheric Observatory in Puerto Rico are described in some detail. Instruments in which the resolution is improved without a corresponding increase of collecting area, such as the cross-type antennas, are briefly described. The future progress of radio telescope design is certain to follow the development of parabolic dishes to still greater sizes, and the exploitation of synthetic antenna systems; the article concludes with a survey of both developments.     

THz 遥感技术的应用进展

近年来,在射电天文学、大气科学发展的推动作用下,THz 时域光谱技术发展迅速,被广泛地应用于遥感领域。介绍了与THz 遥感相关的技术和应用,包括地球观测系统和射电天文学,突出了THz 遥感技术与其他学科之间的紧密联系,显示出了巨大的应用前景。美国、欧洲、日本在THz 遥感领域起步较早,拥有一些成熟的技术和设备;中国起步较晚,技术上和国际先进水平还有一定差距。     

Biography - George Clark Southworth

Born at Little Cooley, Pennsylvania, on August 24, 1890, Dr. Southworth did undergraduate work at Grove City College and graduate work at Columbia and Yale. Then for ten years he was a teacher and for many more years a research worker on the various frequency frontiers of radio. Beginning with experimental work at Grove City College prior to World War I and continuing with research work at the Bureau of Standards and Yale University during World War I, he has been with the Bell System since 1923. He is the author of a score or more of scientific papers on such diversified subjects as ultrashort waves, the dielectric properties of water at ultrahigh frequencies, radio wave propagation, antenna arrays, earth currents, and radio astronomy, as well as that for which he is best known, waveguides. His work culminated in 1950 in a 675-page textbook on microwave techniques, " Principles and Applications of Waveguide Transmission."     

FY-2气象卫星信号的开发利用

详细介绍了基于风云二号静止气象卫星信号实现电离层闪烁监测、云图接收、太空环境参数接收的设备设计、构成。该设备主要用于实时监测分析风云二号卫星信号因电离层变化而造成的幅度闪烁和相位闪烁。由于静止卫星不存在运动所附带的变化,利用其稳定的L波段遥测信号来监测电离层闪烁,优越性显著。风云卫星展宽云图接收设备目前已遍布全国,该设备在其跟踪遥测及云图接收的基础上进行开发,易于组网监测。电离层闪烁监测的结果,将对空间的探测和通讯技术的发展具有重大的意义。     

太空美术与科学普及

太空美术,也是天文美术和航天美术。它体现了天文、航天,以及太空技术方面的探索发现的成果。在天文学教育、天文学普及和太空探索领域内,太空美术占有非常重要的位置。近20年来,中国的报纸、杂志和电视节目在传播太空美术成就方面做出了不少努力。     

Radio Astronomy and Spectrum Management: The Impact of WARC-79

As a valid use of the radio spectrum and an official radio service, radio astronomy was very much a part of the 1979 World Administrative Radio Conference (WARC-79). The allocation of frequency bands is vitally important for the sustained health of the science. WARC-79 provided first the impetus for astronomers, worldwide, to examine the allocation requirements of radio astronomy and then the opportunity to communicate those needs to the regulatory community. The characteristics of radio astronomy, the criteria for interference-free operation, possibilities for sharing with other radio services, and the need for frequency-band allocations are discussed because all bear directly on an evaluation of the Conference. The Final Acts of WARC-79 are examined from the viewpoint of their impact on radio astronomy.     

A subspace-tracking approach to interference nulling for phasedarray-based radio telescopes

Several next-generation radio telescopes, now in the planning stages, are based on phased-array technology. One reason for this is to make use of adaptive nulling techniques to combat radio frequency interference, which is a growing problem for radio astronomy. This paper presents a low-complexity approach to interference nulling which is suitable for use in such systems. The approach uses subspace-tracking to identify interference, followed by spatial projections to place deep nulls in the directions of interferers. This technique overcomes two limitations of power-minimization algorithms (e.g., "minimum variance"), namely power inversion and pattern rumble, which create serious problems for radio astronomy. Furthermore, this technique imposes a lower computational burden and provides side information which is useful in later stages of data processing. Performance results from a phased array demonstrator system and a simulation are presented     

浅谈对卫星广播电视信号的各种影响

卫星广播电视是当前广播电视解决覆盖最有效、最先进、最便捷的途径,但卫星信号到地面,电波经过的距离很远,会受到其他通信信号、大气层（对流层、电离层等）、太阳、宇宙噪声、流星等各种具体影响。     

超流氦制冷系统在空间红外天文观测中的应用

阐述了空间红外天文观测的发展,针对其中较先进的两颗卫星(SIRTF和ASTRO-F),研究了其低温系统的构成,总结出了制冷的工作原理,指出了氦制冷在空间应用所存在的关键技术问题,并对其研究进行了展望。     

The potentialities and present status of masers and parametric amplifiers in radio astronomy

The paper reviews the potentialities and present status of maser and parametric radiometer systems in the whole field of radio astronomy, including radar astronomy. A short historical account of the development of the maser is followed by an outline of the objectives of radio-astronomical research, and the radiation mechanisms which arise. After an account of the requirements of the radio astronomer, a detailed discussion is presented of the limitations and relative merits of masers and parametric amplifiers in this field of research. The paper includes a compilation of data on existing and planned observatory installations. This data has been gathered from published work and from replies to a questionnaire which was widely circulated by the author; it embraces, it is hoped, most of the currently available information. Finally, there is a brief summary of some of the achievements in astronomy which have resulted directly from the developments and applications of these low-noise devices. A few notes are added, in conclusion, as pointers to the likely trends in the near future.     

Detection and estimation practices in radio and radar astronomy

A review is given of detection and estimation methods in current use in radio and radar astronomy. Methods of determining position and brightness distribution of radio sources by narrow-beam antennas, interferometry or lunar occultations are discussed. Observational procedures for the estimation of frequency spectra are explained. The fundamental problem in radar astronomy, viz., that of mapping, is reviewed, and several methods for the removal of ambiguities are considered. Schemes for the determination of range and velocity of a planet are also described.     

The pointing calibration of the Haystack antenna

We have applied techniques of optical astronomy to calibrate the pointing of a high-resolution pencil-beam antenna by using radiometric measurements of cosmic radio sources. The Haystack antenna, a 120-ft paraboloidal reflector on an azimuth-elevation mount, was calibrated at a frequency of 15.25 GHz. The beamwidth at this frequency is 36 millidegrees; the rms residual pointing error after calibration was 2.90 millidegrees in azimuth and 3.45 millidegrees in elevation. A total of 172 measurements of pointing error were made on eight sources, and these data were fitted by the method of least squares to determine seven instrumental parameters that take into account axis-alignment errors and gravitational effects on the antenna structure. These techniques are not restricted to antennas used as radio telescopes, and they may be useful in the pointing calibration of other antennas.