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     

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     

The mechanical design and kinematics accuracy analysis of a fine tuning stable platform for the large spherical radio telescope

A large Stewart platform for fine tuning of the feed source tracing is presented in this paper. The model of kinematics control is developed with coordinate transformation, and a quasi-static load analysis is made by virtual work principle with Jacobian matrix because the tracing speed is slow. The kinematics accuracy model is derived by position vector analysis, and the kinematics accuracy results are provided. It has shown that the designed Stewart platform can satisfy the requirement of feed source trajectory control of large spherical radio telescope.     

The wind-induced vibration control of feed supporting system for large spherical radio telescope using electrorheological damper

Considering the wind-induced vibration of the feed supporting system with cables for the optomechatronics design project of next generation large spherical radio telescopes, a prototype of adaptive electrorheological (ER) damper is designed to realize additional damping control of this vibration. The model of wind is first developed to implement this design and simulations. The model of the designed ER adaptive damper is described in detail, and the strategy of additional damping control using the controllable field-dependent damping force of the ER damper to counteract the wind force is proposed. The numerical simulation results have shown the validity of the designed adaptive ER damper to suppress the wind-induced vibration of the feed supporting system, and the additional damping vibration amplitude can be suppressed to one-half of the original amplitude without ER damper.     

A line feed for a spherical reflector

A line feed for a spherical reflector is considered on the basis of a plane-wave spectrum of radiation angles. It is shown that a feed excited by circumferential slots results in a gain deterioration of at least 3 dB. The correct excitation of the feed is indicated. Expressions for field components in the focal region are obtained.     

A high-performance line source feed for the AIO spherical reflector

An aberration-correcting line source feed has been designed, modeled, constructed, and tested in the Arecibo reflector. The feed is a linearly polarized flat wavegnide 40-foot-long array illuminating 700 feet of the 1000-foot-diameter spherical reflector at 318 MHz. The antenna, illuminated by the new feed, yields an aperture efficiency of 70 percent with a peak gain near 56 dB, half-power beamwidth of 16.2 minutes of arc, and sidelobe levels below 4 percent of the on-axis gain. Vignetting losses are approximately 30 percent at the highest zenith angle.     

Sectoral hoghorn: a new form of line feed for spherical reflector aerials

A sectoral hoghorn may be used as a line feed to correct spherical aberration in an offset spherical reflector. The bandwidth of this type of feed is considerably greater than that of other line feeds, and the construction is simple. The results of measurements on a prototype X band hoghorn are reported, and a technique for reducing the area of spherical reflector required for a given scan angle is described.     

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.<>     

Effect of feed array configuration on the Field-of-View of radio telescope antenna

Phased Array Feed (PAF) is a small two-dimensional phased array antenna, playing a role as the multi-beam feed for the reflector antenna. The prominent capability of large continuous Field-of-View (FoV) coverage and fast survey speed makes PAF the promising feed for radio telescopes. In this paper, the effect of feed array of PAF on the gain fluctuations over FoV is analyzed on a simplified model of the Five-hundred-meter Spherical Aperture radio Telescope (FAST), including illumination pattern edge taper, element spacing, element arrangement and element amount. And the differences between rectangular and hexagonal array arrangements are compared. The relationship between the FoV and array configuration are concluded at last.     

Analysis of active surface reflector antenna for a large millimeterwave radio telescope

The authors analyze the effects of imperfect segment alignment on the aperture efficiency of a large millimeter telescope. A 50 meter diameter instrument of this type specified to operate to wavelengths as short as 1 mm is being designed with an actively controlled main surface. By simulating the performance of the control system, they generate samples of tilt and piston errors for the segments from which the antenna radiation patterns and aperture efficiencies are calculated. They make a comparison of these results with models of antenna tolerance theory developed by Ruze (1966), which relate the aperture efficiency to the RMS phase error. They find that Ruze's formulas have a different range of validity when the aperture RMS phase error, rather than the RMS surface error, is used as a parameter. When appreciable tilt errors are present in large segmented antennas, the aperture RMS phase error tends to a constant value, independent of the aperture illumination and of the shape of the segments. They conclude that the antenna RMS surface error is a better tracer of the aperture efficiency than is the aperture RMS phase error when Ruze's formula is used. They find that this well-known expression stands as a lower limit to the performance of large segmented reflector antennas     

The designing, manufacturing, and testing of a dual-band feed system for the Parkes radio telescope

This paper presents the designing, manufacturing, and testing of a dual-band feed system for the Parkes radio telescope (Australia). The feed system consists of a coaxial horn and associated feed components to operate in the 648-712 MHz and 2.6-3.6 GHz frequency bands. The manufacturing of such a feed system was challenging, and we present the innovative solutions that were devised to fabricate the different parts of the feed system. Preliminary measurements indicate that the overall system, feed and reflector, is working to operational expectations, and valuable scientific results have already been obtained using the simultaneous dual-frequency capability.     

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.     

输电线路大跨越钢管塔的应用和结构设计研究

本文回顾了钢管塔结构发展以及介绍了钢管塔在行业内外使用情况,结合了钢管塔的结构特点,分析了钢管塔荷载计算和动力效应问题,并钢管塔的内力和材质的选择做了详细的概述.     

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.     

输电线路大跨越钢管塔的应用和结构设计探讨

在设计要求方面,这篇论文有严格的要求,从一方面说,就是要越过一种结构——钢管：有结构选型、荷载计算、动力效应、钢材选用、内力分析、节点型式、构,加上之前在设计钢管的过程中有的一些惨痛的经验教训。可以结合一些专家的看法。     

A NEW ADAPTIVE EQUALIZER STRUCTURE FOR NONLINEAR CHANNELS

Based on the analysis of nonlinear channel models,a new connectionist model ofadaptive equalizer is constructed.Comparing with the connectionist model using the Volterraseries to extend the input vector space,the number of weights with the new structure is reducedsignificantly.It is shown by simulations that the weight values of the new scheme converge to theoptimal values closely for non-minimum phase channels as well minimum phase channels,if thechannel noise is small enough.Testing results of the BER(Bit Error Rate)tell us that the newadaptive equalizer for nonlinear channels is superior to the conventional linear equalizers in theequalization performances.     

Full-wave analysis and design of a new double-sided branch-linecoupler and its complementary structure

A new double-sided branch-line coupler using microstrip lines as input/output lines and slotlines as branches is analyzed and designed. The even-odd mode theory is first used to analyze the ideally simplified circuit model and to find out the preliminary circuit dimensions. Based on these dimensions, the full-wave spectral domain approach (SDA) is employed to accurately simulate the circuit performance. By the formulation of the exact Green's function in the spectral domain, the effects of surface wave and radiation phenomena are accurately accounted for. Experimental data agree very well with the SDA simulation results. It is found that the even-odd mode theory which neglects discontinuities between lines is not enough to design a coupler. The SDA code can then be used to accurately simulate and optimize the circuit performance. The complementary structure with slotlines as input/output lines and microstrip lines as branches is also investigated both theoretically and experimentally. It is noticed that the radiation and leakage from the two double-ended branches for all structures will deteriorate the circuit performance     

Diffraction analysis of line feeds for spherical reflectors

The diffraction limitations of the line feeds for spherical reflector antennas are analyzed by means of an asymptotic transition region theory (TRT). It is shown that diffraction from the ends of the line feed causes a broad 6-dB-deep central dip in the aperture field of the reflector. The corresponding reduction in aperture efficiency and increase in spillover are also calculated by means of the TRT. The accuracy of the theory is checked by numerical evaluations of the array sum expression for the radiation field and of the secondary aperture-field and spillover integrals. The results are applicable to the line feeds of the spherical reflector antenna of the Arecibo Observatory     

Sidelobe levels of a large radio telescope employing a combination of physical and resistive tapering

The main beam, sidelobe levels, and effective collecting area of a proposed radio telescope array, operating at 12 MHz, are considered. The telescope consists of two large rectangular arrays containing several thousand half-wave dipoles arranged horizontally in a tee shape above a ground plane. A narrow beam is formed by cross-correlating the outputs of the individual arms of the tee. The possibility of sidelobe reduction using a form of physical tapering consisting of reducing the width of each rectangular arm at appropriate intervals along the array is assessed, by comparing the performance achieved with this type of taper to that obtainable with the more common resistive taper. It is concluded that when the effects of random errors in element excitation are considered the performance of the physically tapered and resistively tapered arrays compares favorably.