一种新型毫米波馈电系统

介绍一种新型开放式毫米波馈电系统－－超导准光系统,该系统已成功地应用于我国１３．７ｍ口径毫米波望远镜上,它工作于２．６ｍｍ波段,已成功进行天文实测和天文研究工作。该系统应用了一个新型４Ｋ低温致冷系统,可工作于二个频段。文中详细介绍了该系统的设计理论及研制结果。实测结果表明,整个系统的插损在２．６ｍｍ波段仅０．１ｄＢ,这种损耗比起波导系统而言是极其微小的,接收机的系统噪声温度在８５ＧＨｚ￣１１２ＧＨ     

A new dual-reflector feed system for the Nancay radio telescope

A new compact dual-reflector Gregorian feed system has been designed to improve the overall performance of the Nancay radio telescope. To operate continuously within the 1.0-3.5-GHz band, two wideband compact corrugated horns are used. The new feed system improves the sensitivity of the telescope by a factor between 2 and 3. To verify the theoretical design, a 1/20th-scale model was constructed and tested. The measured results were in excellent agreement with the predicted values     

A deformable subreflector for the Haystack radio telescope

A deformable subreflector was designed and implemented to compensate for part of the gravity deformations of the primary reflector of Haystack, a 37-m-(120-ft-)diameter Cassegrain radio telescope. This was done to allow it to operate at 100+ GHz, as compared to the 1-to-10 GHz range for which it was originally designed. The design, analysis, construction, testing, and the results of preliminary measurements of performance are presented. The deformable subreflector consists of a fiberglass shell, supported on an aluminum back structure. The homologous components of deformations are compensated for by optimal positioning of the subreflector, which can be displaced axially and laterally, and tilted. The deformation modes of the subreflector compensate for astigmatic deformations of the back structure of the primary, and for part of the symmetric and anti-symmetric components of gravity sag of the panels of the primary reflector. Analyses show that, due to the deformable subreflector, the surface RMS due to gravity has been reduced from 494 mm (19.4 mil) down to 146 mm (5.7 mil), as the antenna travels over its operating range of 15 to 70 degrees elevation. Combining the reduced gravity effects with surface adjustment and thermal errors results in a predicted combined surface error of 250 mm (9.8 mil), at the extremes of the operating range.<>     

Free-space optical distribution of local oscillator signals inaperture synthesis radio telescope arrays

An alternative to individually phase-stabilised links for distribution of local oscillator (LO) signals in large arrays of radio telescopes is considered. An array is illuminated from an elevated optical source, intensity modulated at the LO frequency. LO phase feedback from the centre of the illuminated zone counteracts tower and atmospheric instabilities, locking a fixed phase at zone centre, and hence a template of constant phase contours around the zone centre point. Other LO detector planes are aligned to equiphase contours, providing a phase coherent LO to all telescopes aside from differential optical path effects. A local PLL at each site reduces the remaining noise from differential slant path variations     

Coherence theory of a radio telescope

A new theory is developed to describe the operation of a radio telescope consisting of an array of two-element interferometers. The theory is based on recent developments in the theory of partial coherence, which employs an expansion of the scalar field amplitude into an angular spectrum of plane waves. Expressions are found describing the correlation of the field amplitudes in the antenna plane which are more general than usually obtained, and which suggest a simplified data processing procedure which might yield improved images. The usual quasi-monochromatic approximation is made and the conditions under which it is valid are discussed in detail. Finally the theory is connected with the usual procedure for producing images of the radio sources and the existence of an obliquity factor is shown which could affect images over a large field of view.     

A supersynthesis radio telescope for neutral hydrogen spectroscopy at the dominion radio astrophysical observatory

A radio telescope designed for studies of the 21-cm line of neutral hydrogen is described. It combines the techniques of aperture synthesis and digital correlation spectrometry to achieve an angular resolution of 1 arc min within an area of sky of 2° diameter and a frequency resolution variable from 3 to 100 kHz with 80 channels. The telescope comprises four 9-m paraboloids, two fixed and two movable on a 300-m precision E-W track. The system noise is 80 K. Remote local oscillators are controlled in phase to about 1 degree independent of the electrical lengths of distributing cables. An on-line computer provides source positions, and controls telescope tracking, local-oscillator frequency and phase, and incremental delay compensation. It also performs the Fourier transformation of the correlation coefficients and the data logging. The digital correlator uses 3 by 5 level quantization which reduces signal-to-noise degradation due to quantization to a factor 1.16. The telescope sensitivity for emission and absorption studies is discussed and first results are presented.     

Gain calibration methods for radio telescope arrays

In radio telescope arrays, the complex receiver gains and sensor noise powers are initially unknown and have to be calibrated. Gain calibration can enhance the quality of astronomical sky images and, moreover, improve the effectiveness of array signal processing techniques for interference mitigation and spatial filtering. A challenging aspect is that the signal-to-noise ratio (SNR) is usually well below 0 dB, even for the brightest sky sources. The calibration method considered here consists of observing a single point source and extracting the gain and noise parameters from the estimated covariance matrix. We present several closed-form and iterative identification algorithms for this. Weighted versions of the algorithms are proven to be asymptotically efficient. The algorithms are validated by simulations and application to experimental data observed at the Westerbork Synthesis Radio Telescope (WSRT).     

The 100-meter radio telescope at Effelsberg

The 100-m fully steerable radio telescope of the Max-Planck-Institut für Radioastronomie (MPIfR) has now been in service for over a year. The telescope was designed to allow observations in the decimeter and centimeter wavelength regions, with the vastly improved resolution given by the 100-m diameter. During construction of the telescope measurements were made at a wavelength of 75 cm. Since the completion of the adjustments, tests and observations were made at 11-cm and 2.8-cm wavelengths. In particular, at the 2.8-cm wavelength, tests have fully confirmed the design goals. In fact, we hope to extend the operational range of the telescope at least to the wavelength of 1.2 cm. A number of problems, new in this field, had to be solved in the construction of an instrument of this size and precision. Measuring methods are described which allowed adjustment of the surface to ±1 mm. A computer-controlled servo loop allows setting of the telescope to 5". Experience of operation under various conditions is described.     

Multibeam-operational mode at the RATAN-600 radio telescope

The main requirements for the feed array designed for the RATAN-600 radio telescope, which are intended to improve observational possibilities, are presented. The experimental eight-element feed-array assembly and its measured characteristics are described. The first antenna measurements, made in the AC operational mode, shown that the combination of the reflector with the feed array may increase the reflector's facility. The equipment described could be used for radio-astronomical observations at the RATAN-600, but it is clear that the best results will be achieved with the use of a 32-element feed array     

Measuring the gravitational astigmatism of a radio telescope

Most conventional radio telescopes will show a strong astigmatism when tilted, resulting in surface degradation, which can be corrected with a mechanically deformable subreflector. Astigmatism means different focal lengths (Delta F) in two perpendicular planes. A most direct way of measuring the astigmatism is to measureDelta Fwith an elongated rotatable feed, illuminating only a central strip of the telescope. Equations are given for the relations betweenDelta F, rim deviationA, and rms surface deviationDelta z, and for the dependence of these quantities on elevation angle. This method was applied to the 140-ft. telescope. Between zenith and horizon, the measured range isDelta F = (51 pm 2)mm, yielding an astigmatic rim deviation ofA = 8.7mm, and an astigmatic rms surface deviation ofDelta z = 2.87mm. The latter agrees with astronomical efficiency measurements, showing that the total gravitational deformation is mainly of a simple astigmatic shape, to be corrected by relatively simple means.     

The Parkes radio telescope modified for rapid receiver changes

This paper describes improvements to the Parkes 64 m radio telescope. It is being upgraded to allow rapid switching between receivers, and to track the best-fitting focus as the elevation angle changes. Carried out under contract on behalf of NASA, the upgrade included installing a low-noise 2.3 GHz receiver for tracking the spacecraft Galileo in 1997. We explain the mechanical and structural aspects of the upgrade, including the need to replace the existing focus cabin with a larger unit, and the effect of the increased weight at the prime focus on the focusing characteristics and reflector accuracy. Finally, we summarize the designs of the feed and receiver to optimize the antenna-efficiency/temperature ratio at 2.3 GHz for the Galileo mission     

太阳射电望远镜控制及采集系统研究

天文学是一门观测的科学,而望远镜就是人们观测天体的工具。国内的太阳射电望远镜大多数采用的是伺服电机驱动,体积巨大,价格也不菲。所以,文中研制一种轻巧,性价比相对而言比较高的太阳射电望远镜。太阳射电望远镜运用的是一个改进的直流电机驱动小型抛物面天线转动,能实现对太阳的跟踪,监测并记录太阳辐射天线温度值的变化,监视太阳爆发并记录太阳射电爆发资料。     

Upgrading the Haystack radio telescope for operation at 115 GHz

The Haystack 37-m radio telescope has been upgraded for operation at frequencies up to 115 GHz. A unique deformable subreflector with active actuator control has been developed to correct for gravitational distortion effects including astigmatism and deflections associated with the particular reflector surface. Active thermal compensation of the surface has also been implemented to conduct for both thermal lag effects and circularly symmetric gravitational deviations. Holographic mapping of the antenna surface deviations was achieved using 12-GHz geostationary satellite transmissions, which required the use of special techniques to correct for diffraction and multiple reflection effects involving the space-frame radome that covers the antenna. Realignment of the antenna surface utilized a finite-element structural model to translate surface deviations to motions of the unusual adjustment mechanisms on the antenna. The currently measured rms surface deviation (Dec. 23, 1992) is 210 μm. The telescope has been equipped with a two-channel cryogenically cooled 3-mm SIS receiver, covering the range from 84 to 115 GHz. A new flexible digital spectrometer has been constructed for spectral line astronomy. Configurations can range from a widest bandwidth coverage of 160 MHz at 512 lags to 0.66 MHz at 4096 lags. Examples are given of surface holographic maps and radio measurements of aperture efficiency, pointing, and other performance parameters     

带金属盒的月球射电仪天线特性研究

选择RWG和Costa基函数用矩量法分析了线面结合的天线问题,计算了月球射电仪典型天线的输入阻抗和方向图.给出了单极和双极天线的典型结果,得到了金属盒大小对结果的影响关系.对于双极天线还对比了中馈和边馈两种方式的结果.在计算中,使用了9点高斯积分法处理奇异积分,得到了较好的效果.