The characteristics of the radome-enclosed Haystack antenna have been evaluated as a radio-astronomical instrument. Important advantages of the radome enclosure are the high pointing precision it permits under all wind conditions, the rms pointing errors being 7" in azimuth and elevation, and the antenna surface tolerance (0.027 in rms) made possible by controlled environment. We searched for but failed to find any detectable radome effects as follows: pointing deviations, gain variations, noise granularity, and polarization effects. The principal electromagnetic effect of the radome is a reduction of aperture efficiency by an amount that varies from about 1 dB at long wavelengths to 2.8 dB at 35 GHz. The noise contribution is about9degK at 8 GHz and21degK at 22.2 GHz. View full abstract»

A broad-band antenna element and beam-forming matrix have been developed for reception of signals at 25-100 MHz. The element is a zig-zag log-periodic antenna with a nominal impedance of430Omegaand a VSWR of less than 1.9. The matrix utilizes time-delay gradients to obtain frequency-independent beam positions and also allows several different beam positions to be monitored simultaneously. Observations of natural radio sources using a 16-element array have verified its usefulness. View full abstract»

A general expression is derived for the maximum angular accuracy of tracking a radio star by lobe comparison (or monopulse). This angular accuracy depends on the input signal-to-noise ratio, the wavelength, the time-bandwidth product of signal integration, and the effective length of the antenna aperture. The maximum angular accuracy can be obtained, approximately, by performing a simple correlation of odd and even components of the antenna output. Angular accuracy formulas for simple antenna dishes or for interferometers appear as special cases of the general result. The Appendix discusses the interferometer technique in more detail, and the angular accuracy for the data processing technique used by M. Ryle is compared with that obtained from the optimum processing. View full abstract»

The application of orthonormal basis functions such as Prolate Spheroidal Wave Functions (PSWF) for accurate source modeling in radio astronomy has been comprehensively studied. They are of great importance for high fidelity, high dynamic range imaging with new radio tele- scopes as well as conventional ones. But the construction of PSWF is computationally expensive compared to other closed form basis functions. In this paper, we suggest a solution to reduce its computational cost by more efficient construction of the matrix kernel which relates the image domain to visibility (or Fourier) domain. Radio astronomical images are mostly represented using a regular grid of rectangular pixels. This is required for efficient storage and display purposes and moreover, comes naturally as a by product of the Fast Fourier Transform (FFT) in imaging. We propose the use of Delaunay triangulation as opposed to regular gridding of an image for a finer selection of the region of interest (signal support) during the PSWF kernel construction. We show that the computational efficiency improves without loss of information. Once the PSWF basis is constructed using the irregular grid, we revert back to the regular grid by interpolation and thereafter, conventional imaging techniques can be applied. View full abstract»

A technique is described for adjustment of phase paths within large antenna arrays or paraboloidal surfaces which are now in use, or are planned, for radio astronomy. After large paraboloids have been constructed, they suffer distortions which are very difficult to investigate and for which photogrammetry, millimeterwave radar and optical survey have been suggested. A new suggestion, based on experiment at Stanford with phase measurement of long paths, is to place modulated gas discharge tubes, acting as scatterers, at various points on the paraboloidal surface and to monitor the phase path from a signal generator through the feed at the focus to each discharge tube in turn, and back. By means of a second probe, say a dipole situated at the vertex of the paraboloid, it is possible to triangulate on deflections. The feasibility of this scheme has been established in connection with the large Stanford cross antenna which has an aperture of 1339 wavelengths at 9.1 cm. The phase of the modulated reflected wave produced by the discharge tube is determined by adding it to a reference continuous wave of large amplitude and applying the resultant to a receiver sensitive to the modulating frequency. A null is obtained when the two waves are in quadrature. The coherent detection system allows measurement of the phase of the modulated reflection even when its amplitude is below -130 dbm. Using a 10-mwS-band signal generator, no difficulty was found in detecting the reflection from a small discharge tube placed 100 feet away from a 3 by 4 inch horn, which is sufficient range for applying the method to large paraboloids. View full abstract»

A pseudo-frequency-independent beam waveguide feed has been designed and built to accommodate a new liquid-helium-cooled millimeter wave radio astronomy receiver in the side cab of the Crawford Hill 7-m antenna. This enables the antenna to be tilted without tilting the liquid-filled receiver. Comparison with the old vertex-cab feed indicates very little measured transmission loss through the beam waveguide. The frequency independence is based upon the Fresnel zone imaging principle. Design procedures and practical bandwidth limitations are explained. An explicit expression for the third-order term of an offset reflector surface clarifies the approximation of a lens by an offset reflector. View full abstract»

Surface plates with four adjustment screws, one at each corner, allow four degrees of freedom for their adjustment, including an internal nonplanar twist or warp. Thus the surface deformations of trapezoidal plates under enforced twists are investigated. A simple equation is derived, holding as a satisfactory approximation for various plate designs (solid plate, honeycomb, and skin-and-ribs). Measurements at four different experimental plates agree with it within 2 percent. This approximation is then used to develop a least-squares procedure for obtaining those adjustment amounts which minimize the root-mean-square (rms) deviation between the plate's surface and the desired telescope paraboloid. The resulting procedure is recommended for all telescopes with trapezoidal surface plates. Seven experimental plates of four different designs were tested in the lab, and the suggested least-squares procedure (as compared to a simple true-corner adjustment) improved the residuals by 27 percent. Measurements of some plates on a telescope gave also encouraging results. View full abstract»

A two-element radio interferometer operating at 8.33- mm wavelength has been developed at the Jet Propulsion Laboratory's Table Mountain Observatory near Wrightwood, CA. The interferometer employs a 5.5-m and a 3-m diameter antenna on an east-west baseline of 60 or 120 m, yielding fringe spacings at transit of 28" or 14", respectively. The broad intermediate-frequency bandpass of 100- 350 MHz and the system noise temperature of 500 K provide high sensitivity for the measurement of continuum sources. The interferometer has been used for high-resolution studies of the planets and the Sun, and it is currently being adapted to study solar flare emissions at high spatial and time resolution. View full abstract»

The Atacama large mm/sub-mm array (ALMA) has antennas arrayed over baselines up to 18 km in extent which will constitute over 7000 m² of collecting area, enabling it to provide images of unprecedented clarity and detail. Unlike existing arrays, it will combine interferometric and single telescope data, providing a complete range of spatial scales with complete flux recovery. Six of a planned ten planned receiver bands will be built during the construction phase; eventually ALMA will cover all atmospheric windows in the spectral wavelength ranging from 7 mm to 0.3 mm. The combination of sensitivity, directivity, full UV coverage, precision calibration and the breadth of coverage, along with the extremely dry Chajnantor site at 16500 feet, will enable the creation of superb images of the celestial structures which emit mm and sub-mm photons. Equipment will continuously monitor atmospheric parameters, in particular the water vapor content along the telescopes' line of site, to permit real time correction of atmospheric perturbations to the observed wavefront. The observer will have a range of sophisticated data analysis techniques to be able to compensate for atmospheric and instrumental perturbations to the raw data. View full abstract»

Reflectivity (reflection loss) investigations of nickel samples with different types of surface finish, with and without rhodium coating, have been carried out in the 110-200 GHz frequency range on an installation developed in the Applied Physics Institute of Russia. The reflectivity measurements of high quality silver coated and gold coated mirrors are also presented. The reflectivity (reflection loss) investigations of some carbon fibre samples with and without aluminium coating have been made. Results are interesting, in view of the anisotropy of the carbon fibre material. View full abstract»

Currently a plan to convert a 32 m telecommunications antenna in the Peruvian Andes at 3370 m above sea level into a radio astronomy facility is in progress, it will be operated by the Institute of Geophysics in Peru (IGP) and local universities with assistance from the National Astronomical Observatory of Japan (NAOJ). In this paper we show progress on the project. View full abstract»

The beam efficiency of an antenna may be defined as the ratio of the power radiated within the main beam to the total power radiated. The beam efficiency is derived for ideal rectangular and circular apertures, as a function of the edge-to-center amplitude ratio. Random phase errors are assumed to exist across the aperture. Various types of feeds for parabolic reflectors are also considered in relation to the fraction of power which the feed directs into the paraboloid. A primary limitation on the beam efficiency of a paraboloid is shown to be produced by the surface roughness. View full abstract»

The best position for the rotation axis of the wobbling secondary mirror in a Cassegrain type of antenna is through the focal point of the main mirror: the prime focus. Compared to the usual situation, where the axis of rotation contains the vertex of the secondary mirror, this means a considerable improvement of beam quality, especially at large wobble angles. View full abstract»

This paper provides an overview of MeerKAT, the South African Square Kilometre Array (SKA) precursor array that will form an integral part of phase 1 of the SKA. The telescope is located in the central Karoo in South Africa and the site is briefly described. The dish and feed, correlator and overall array design are discussed, as is calibration, imaging and RFI mitigation. MeerKAT as an example of mission driven innovation is considered. Planned MeerKAT science is briefly outlined. The paper concludes with a summary of plans for SKA phases 1 and 2. View full abstract»

A 960-Mc two-element interferometer using the twin 90-foot steerable paraboloids of the California Institute of Technology Radio Observatory is described. The response of the associated receiving equipment as it applies to interferometric position measurements is analyzed in some detail, and an advantage of not rejecting the image response of the receiver is mentioned. Finally, a brief account is given of the various ways the interferometer may be used to measure right ascensions and declinations with both an east-west and a north-south baseline. View full abstract»

This review looks at the history and present state of microwaves in the Ukraine, showing that this area is well developed and has great potential. The Ukrainian microwave community is comparable to that in such nations as France, Germany, Italy and the United Kingdom, although today it is scarcely funded. The review also covers microwave research, industry, and education in the Ukraine. View full abstract»

Strong cosmic radio sources provide a constant broadband and accurately positioned test transmitter for measurements of large antennas. Some sources have their flux density determined absolutely and can be used to calibrate the antenna gain. This paper presents up-to-date data on the radio sources which are useful for antenna measurements. The measurement of pointing and focusing corrections is discussed. The main part of the paper is concerned with the derivation of major antenna parameters such as aperture and beam efficiency, beam solid angle, sidelobe levels, error pattern characteristics from measurements on radio sources. The effects of a finite angular source size are discussed, and it is shown how measurements on sources of different size increase the information on the derived antenna parameters. The methods to measure very weak sidelobes are treated and the external factors, solar and galactic radiations influence of the earth and atmosphere, which might limit the accuracy of the measurement are described. The paper takes a practical approach to the subject and contains graphs with numerical data. View full abstract»

A pencil beam interferometer has been constructed at Stanford, Calif., with multiple beams of 3.1 minutes of arc width to half power (0.8 microsteradian). It is composed of two equatorially-mounted, 16-element, Christiansen arrays of 3-m paraboloids, each 375 feet long (1255 wavelengths at a wavelength of 9.1 cm). The half power beamwidth of the fan beam of a single array is 2.3 minutes of arc. To form the pencil beam, the two arrays are switched together as in a Mills cross. Frequency range is from 2700 to 3350 Mc. Phase adjustment and monitoring are handled by a new technique of modulated, weakly reflecting gas-discharges maintained at the focus of the paraboloids. Television-type scanning yields maps of the sun (spectroheliograms) revealing fine details of the microwave source regions in the chromosphere and corona. All the transient bursts and a large fraction of the steady solar emission at 9.1 cm prove to originate in a small number of highly compact centers, whose brightness temperatures may exceed5 /times 10^{5}/degK. The sensitivity of the instrmnent also allows the thermal emission from the moon (250/degK) and a number of galactic and extragalactic sources to be studied with high angular resolution. Illumination of the moon by terrestrial radar can be detected. The pencil beam interferometer furnishes the finest beams currently available from pencil beam antennas of any type. Examination of the fundamentals of extracting high resolution details of a source from its radiation field indicates the fitness of pencil beam interferometers, incorporating steerable multielement arrays, for future development to higher resolving power. Adequate technique of phase preservation over wide spacings is available. View full abstract»

The resolution capabilities of a variable baseline correlation interferometer are analyzed using a maximum likelihood estimator algorithm for the output data. Optimum estimates (in the Cramer-Rao sense) for two sources of both equal and unequal strengths, for different levels of receiver-background noise, and for finite integration (averaging) times are obtained. A likelihood probabilityp_{n}(n = 0, 1, 2, 3, ...)is also obtained from the measured data, and the resolution limit is defined to be that for which the probabilitiesp_{1}andp_{2}are equal (on the average). It is shown by a computer simulation that the average resolution limit improves (decreases) with increased integration time, exceeding the traditional Rayleigh limit by an arbitrary amount even for quite unequal source strength ratios and large levels of receiver-background noise. View full abstract»

The methods used to determine the absolute gain of an 80-square foot aperture horn-reflector antenna over a frequency range from 2.8 to 14.0 Gc, and in the absence of a high-level test range, are described. A "mirror" range, in which the size of the smooth reflecting surface required was relatively small, was used and the measurements were performed in the Fresnel zone of the antenna with corrections applied for the resulting gain reduction. These and other provisions reduced the probable error in the final values to about one per cent. View full abstract»

The design of an antenna calls for definite amplitudes and phases of the currents, but when the antenna has been constructed and adjusted, there will be departures from the design currents because of several factors. The customary procedure of taking radiation patterns and making the final adjustments semi-empirically has usually been satisfactory, but two difficulties have been setting in with the trend towards large antennas of high gain. First, it is impossible to measure the radiation pattern of the largest existing antennas; even the determination of single sections through the pattern or the gain in one direction presents difficulty. Second, the adjustments themselves are more laborious on larger antennas. It is therefore very desirable that the theory of antenna tolerances should be pursued so that the effect of departures can be taken into account, statistically or otherwise, during the design. This paper considers the effects of systematic and random errors on the radiation pattern of antennas representable by a field distribution over an aperture, such as paraboloidal reflectors and large arrays of small elements. In the case of paraboloids, the deterioration in directivity is found to depend on the mean square departure of the surface from the paraboloid of best weighted least-squares fit and on the two-dimensional autocorrelation function of the departure. The variation of directivity with wavelength of a particular paraboloid is deduced by leaving out of account those two-dimensional Fourier components of the departure with spatial periods less than a wavelength. Practical steps are considered for unifying testing, adjusting, and design so as to lead to the greatest relaxation of the mechanical tolerances imposed on construction. View full abstract»

A method for producing a constant-phase calibration signal anywhere along a transmission line is discussed. Based on the multiplication of two half-frequency signals flowing in opposite directions along the line, a method has been developed particularly for phasing a large radiotelescope array. This method has been used for the adjustment of the University of Sydney one-mile cross-type radiotelescope; the performance of the system is discussed. View full abstract»

Beam mapping at 1.3-cm wavelength has shown very strong sidelobes at the 140-ft telescope, up to four lobes in a row when pointing far west. Different types of observations and the theory of coma lobes lead in good agreement to the conclusion that the telescope suffers a large lateral defocusing, varying by 7.2 cm east-west (EW) and 2.8 cm north-south (NS) for pointing changes of90deg. Since the lateral deformation of the feed legs is only 0.5 cm, it must be mainly the optical axis which moves. This is achieved by a gliding rotation of the best-fit paraboloid, gliding along a slightly deformed surface, while rotating about the center of the average surface curvature. It is shown that the resulting lateral focal offset can be much larger than the surface deformation which causes it. The gliding rotation is also confirmed by a structural analysis. The observational and analytical methods described can also be applied to other telescopes. Polar mounts such as the 140-ft may show the effect in two directions: east-west and north-south, while alt-azimuth mounts can show it in only one direction: up-down. The effect of lateral defocusing is to be expected at other telescopes as well whenever the rim is more flexible than the center; and the resulting degradation of efficiency and beam shape will be significant whenever gravity is important in the error budget. In these cases the telescopes should be supplied with a variable lateral shift of the mount at the prime focus, computer-controlled as a function of the pointing, following the axial movements. This additional degree of freedom may improve the short-wavelength performance considerable for telescopes whose surface panels are more accurate than the gravitationally deformed backup structure. View full abstract»

In this paper a stepped cylindrical mirror is described which satisfies the following requirements: 1) it is free from spherical aberration for a point source at infinity on the axis, 2) both off-axis spherical aberration and coma vanish for fixed values of the field angle,bar{Omega}, and of the aperture,bar{alpha}. The analysis has been carried out, in the approximation of para-geometrical optics, by considering a diffraction grating of the generalized type, equivalent to the stepped mirror. Three interesting results are obtained, and precisely: 1) independently of the values ofbar{omega}andbar{alpha}, the equivalent diffraction grating has a quasi-parabolic cross section, 2) the off-axis spherical aberration turns out to be negligible over the whole aperture0-bar{alpha}, for fields angles up to at least 20 degrees, 3) the residual coma turns out to be well corrected, too. View full abstract»

Numerical calculations have been carried out and the beam squint for circular polarized excitation has been measured using a 100 m telescope. The telescope was operated in the Gregorian mode, where the equivalent focal length equals 387.5 m. The feed horn was laterally displaced by 1.364 m from the optical axis at the system focus. Good agreement was obtained between the numerical calculations and the experimental results. The authors found a shift of the two radiation patterns of ≃2 arcsec. The orientation of the beam squint in the configuration with a laterally displaced feed is different from the orientation in offset reflector antennas View full abstract»

The number of nonredundant baselines obtained from the T, Y, and ring array configurations are compared. For the same number of array elements, it is shown that the ring array has the largest number of baselines. The Y array has the second largest number of baselines; however, it also has more potential for adjustments and future growth. View full abstract»

In the near field of the Arecibo spherical antenna radar system, i.e., at ranges less than about 260 km, the gain is a function of range and a knowledge of gain is necessary for deducing electron-density information from the power backscattered from the ionosphere. A method of obtaining the phase taper across the aperture (and hence the near-field on-axis and backscatter gains versus range), given a knowledge of the far-field on-axis gain versus frequency, and the amplitude of the illumination over the aperture is suggested. Our studies show that measurements of on-axis far-field gain over a bandwidth ofpm7MHz are adequate to give an accurate indication of on-axis gain versus range in the near field, while apm15MHz frequency spread is needed to give accurate information on the backscatter gain versus range. The near-field correction for the antenna has also been estimated from measurements made on a model of the new line feed. Confidence in the validity of this approach has been obtained by comparing the measured far-field on-axis gain versus frequency with that calculated using the data from the model feed. View full abstract»

We show thatnantennas may be used asmsuccessive linear arrays to give, without redundancy, all the spacings from 1 throughm n(n - 1)/2, form = 4andn = 3, m = 5, andn = 3, andm = 4andn = 4. For every case, solutions are given requiring the minimum number of stations. View full abstract»

The aperture efficiency of the 45-ft Itapetinga reflector was found to be about 50 percent atlambda = 7mm. The reflector surface panels were mechanically measured in 2664 points displaying the presence of slowly varying errors that negligibly effect the aperture efficiency. We confirm that the reflector's aperture efficiency seems to be predictable from mechanical measurements of the surface when the distribution of errors is non-Gaussian, when the surface is only slightly rough in terms of a wavelength, and when the slowly varying errors across the surface are known [1], [2]. View full abstract»

Interferometry has been used for decades to image distant electromagnetic sources at long wavelengths. However, the long data collection intervals have prevented imaging rotating objects such as planets. We show that one can craft an interferometric imaging algorithm using synthetic aperture beamforming techniques by linear beamforming in the correlation domain data rather than the signal-domain data. We then use this analogy to show how it is possible to create previously unrealized interferometric images of a rotating spherical blackbody View full abstract»

In this paper it is shown that by means of a crosscorrelation antenna system it is possible to measure the mutual power distribution,T(u, v), of partially coherent radio sources. The two linear antennas of the system are scanned independently to give a two-dimensional output which can be written asbar{R}(u, v) = T(u, v) ast A(-u)B^{ast}(-v)whereA(u)andB(v)are the patterns of the two antennas. A two-dimensional Fourier analysis of the output shows it to be a smoothed version of the true mutual power distribution. One can define a principal solution,T_{0}(u, v), which is a generalization to two dimensions of the well-known principal solution,T_{0}(u), which occurs when the sources are incoherent. The limiting cases of complete coherence and complete incoherence are considered. It is shown that for coherent sources the principal solution is factorable,T_{0}(u, v)=varepsilon_{0}(u)varepsilon_{0}^{ast}(v). For incoherent sources it is shown that the spatial frequency spectrum ofT_{0}(u, v)is a function of only the difference,x-y, of the spatial co-ordinates,t_{0}(x, y) = t_{0}(x- y). View full abstract»

The radiation properties of a single zig-zag antenna are reported. This is a special type of broad-band traveling-wave antenna which, when properly designed, produces a strong axial beam of radiation. The radiation pattern has a half-power beamwidth of22degin theEplane and28degin theHplane; the corresponding sidelobe ratios are 10.5 db and 17.5 db down, respectively, in the two planes. Approximate expressions for the radiation fields are also given and compared with the experimental values. The broad-band property of the antenna is studied by measuring the radiation patterns over a range of frequencies. The performance of the antenna is compared with the Yagi antenna. The high directivity of the antenna can be utilized advantageously in the vhf and uhf ranges. The results of impedance measurement also are reported. View full abstract»

The 150-foot slotted waveguide antenna for operation on a wavelength of 10 centimeters at the National Research Council, Ottawa, Canada, is now in operation as one element of an interferometer. The other element is itself a simple interferometer with element separation equal to that of the long array and is placed to the west on the common E-W axis. A rotary phase shifter in the arm between the array and simple interferometer is used, after Ryle, with a phase-sensitive detector. The resultant pattern consists of the product of three terms: 1) The single-lobe pattern of the long array; 2) the interference pattern of the simple interferometer, and 3) the interference pattern between the simple interferometer and array. This configuration gives a twofold increase in E-W resolving power over a uniformly collecting aperture of equal dimension. The presence of two interference patterns suggests the name, "compound interferometer," and the new antenna produces a fan-shaped beam2' E-W times 2degN-S. The instrument has been used to obtain daily drift curves of the sun. View full abstract»

The lecture describes some of the scientific characteristics of the 250 ft-aperture steerable radio telescope at the Jodrell Bank Experimental Station of the University of Manchester. Some of the research problems on which the telescope will be used are then outlined against the current background in radio astronomy. These include the study of the background continuum radio emission of the Galaxy and of the galactic radio sources over a wide range of wavelengths. The main programme on the extragalactic radio emissions will involve a study of the spatial distribution of particular classes of extragalactic radio sources and the measurement of their distances, from which it is hoped that significant progress can be made with cosmological problems. The telescope will also be used as a combined transmitter and receiver to make further studies of the moon and possibly the planets. Other items in the programme include the study of very faint meteors by the radio echo technique and various problems of solar terrestrial relation ships of particular importance to the International Geophysical Year. View full abstract»

Many modern radio applications, such as astronomy and remote sensing, require high-precision polarimetry. These applications put exacting demands on radio polarimeters (antenna systems that can measure the state of polarization of radio sources), and in order to assess their polarimetric performance, a figure of merit (FoM) would be desirable. Unfortunately, we find that the parameter commonly used for this purpose, the cross-polarization ratio, is not suitable as a polarimetry FoM unless it is given in an appropriate coordinate system. This is because although the cross-polarization ratio is relevant for raw, uncalibrated polarimetry, in general it is not relevant to the quality of the polarimetry after polarimetric calibration. However, a cross-polarization ratio can be constructed from invariants of the Jones matrix (the matrix that describes the polarimetric response of a polarimeter) that quantifies polarimetric performance even after calibration. We call this cross-polarization ratio the intrinsic cross-polarization ratio (IXR) and conclude that it is a fundamental FoM for polarimeters. We then extend the IXR concept from the Jones calculus to the Mueller calculus and also to interferometers, and we give numerical examples of these parameters applied to the Parkes radio telescope, the Westerbork synthesis radio telescope, and the Effelsberg telescope. View full abstract»

Presented is an image of contours of radio emission from the Great Nebula in Andromeda (M31) measured with The Ohio State University 260-foot radio telescope at 1415 Mc. The radio contours are superimposed on a Perkins Observatory photograph. This galaxy is at a distance of some two million light years and is believed to be quite similar to our own galaxy. The contour interval is 0.05° Kelvin of antenna temperature. The cross indicates the optical center and the small white circle the approximate radio center (Nature, vol. 202, p. 1202; 1964). The figure is about 3.5° wide by 4° high; the antenna beam size is shown at the top. This radio-optical presentation exemplifies the growing trend of combining radio and optical results in astronomical research. View full abstract»

The results of a survey of cosmic radio background radiation at 250 mc using the Ohio State University 96-helix radio telescope are described. The antenna has beam widths of about 1.2° in right ascension and 8° in declination between half-power points. Radio maps, covering about 75 per cent of the sky, are presented in celestial and galactic coordinates. The greater resolving power of the antenna has revealed a number of fine features of the background radiation as well as numerous radio stars. Radio maps made at other frequencies by various groups are summarized. To present an over-all picture of the sky at different frequencies, eight maps are shown for frequencies from 64 mc to 910 mc. All maps are modified to have the same scale, coordinates and units to facilitate intercomparison. An intercomparison of these radio maps shows some consistent features of the galactic background radiation. These features may be represented by three symmetrical distributions and several unsymmetrical or irregular distributions. The symmetrical distributions are as follows: 1) a narrow belt about 3° wide lying in the galactic plane and concentrated towards the galactic center, 2) a very broad band of radiation concentrated within about 15° to 30° of galactic latitude and having its maximum near the galactic center, and 3) an approximately isotropic distribution. The first component indicates a mixture of thermal and nonthermal origin, while the other two are nonthermal. View full abstract»

In recent years, radio astronomy has faced a growing interference problem from commercial communications. Relatively strong signals from different communication devices can cause severe interference to weaker radio signals. A prime threat comes from transmitters in orbiting Earth satellites, since those transmitters are located overhead, precisely where radio astronomers must aim their telescopes to study the universe. For example, the downlink (space-to-Earth) signals from the Iridium satellite system span the range 1621.35-1626.5 MHz (L-Band) and are quite strong. Besides, significant sideband emission from Iridium can sometimes be seen as low as 1619 MHz and can cause harmful interference of up to 30 dB above the levels deemed harmful by ITU. The important OH transition at 1612.231 MHz lies very close to the Iridium downlink signal. The transmissions from Iridium cause disruption to searches for OH megamasers because their signals are nearly always present, and they cover a wide range of frequencies. The scope of this paper is to mitigate the interference caused by the downlink signal of Iridium. An algorithm is presented here to detect the signal from Iridium, estimate the signal, recreate it using estimated parameters and finally subtract it from the radio telescope. The Iridium data used in this paper is obtained from the Argus, an experimental omnidirectional radio telescope developed to detect the L-Band signals (S.W. Ellingston et al.) . View full abstract»

In this paper, a rigorous procedure for calculating the antenna noise temperature is described, and applied to the antenna of BEST-1 (basic element for SKA training - version 1), which represents one of the SKA (square kilometer array) demonstrators. The SKA will be a new-generation radio telescope, with a collecting area 50 times larger than the area of today's largest radio telescope. BEST is the Italian reduced-scale SKA demonstrator, based on the re-instrumentation of about 8000 m² of the Northern Cross radio telescope, built with cylindrical parabolic antennas. In order to perform the antenna-temperature analysis, an electromagnetic tool to accurately evaluate the antenna pattern in the whole space surrounding the antenna itself is required. We used the commercial software GRASP8, developed by TICRA, to characterize reflector antennas. The antenna temperature was evaluated using the guideline adopted by the Antenna Task Force of the SKA world consortium. For BEST-1 at 408 MHz, we found an antenna temperature equal to 30 K in the zenith direction and 60 K at the horizon. The numerical results have been verified through several celestial calibration radio sources. View full abstract»

In the application of active reflector units supporting mechanism for a large spherical radio telescope (Five-hundred meter Aperture Spherical radio Telescope: FAST), a spatial three-degree-of-freedom (DOF) parallel mechanism combining two degrees rotation and one degree translation is investigated. In this paper, the mechanism is described in detail and its inverse kinematics solutions are derived. The parasitic motion of this mechanism is analyzed, and the relationships between the parasitic motions and independent motions of the mechanism are illustrated, followed by the Jacobian matrix of the velocity equation. The distribution of conditioning index on the workspace of the mechanism is obtained. And the workspace of the mechanism is numerically generated. The analysis results prove that the parasitic motion is neglectable compared to the independent motion in this application and the mechanism can be used as the supporting mechanism of spherical radio telescope. View full abstract»

We describe the serendipitous discovery of a very steep-spectrum radio point source in low-frequency Giant Metrewave Radio Telescope (GMRT) images of the supernova remnant(SNR) G76.9+1.0. Earlier studies have shown that this SNR has a bipolar structure within a filled morphology. The steep spectrum, as well as the location of the point source near the centre of this SNR make it a very promising pulsar candidate. Archival Chandra X-ray data shows a point source coincident with the radio point source. However, no pulsed radio emission was detected despite deep searches at 610 MHz and 1160 MHz - which can be understood to be due to temporal broadening of the pulses. We underline the usefulness of low-frequency radio imaging as a good technique to prospect for pulsar candidates. View full abstract»

Over the last three centuries, there have been many advances in optical telescopes. To find planets that may support life like our own planet, astronomers have to search for planets that orbit stars at the "Goldilocks" distance: not so close that they will be unbearably hot "Jupiters," and not so far away that they will be frozen "Plutos." Locating objects within the bright glare of a host star is no easy task. However, as reported in a recent paper in Nature by a Jet Propulsion Laboratory (JPL) group, scientists have made tremendous progress in the field. The JPL group used "wavefront correction" techniques applied to coronagraphs to optically observe a planet orbiting its host 33 light years away, with a relatively small (1.5 m) Earth-based telescope. When it comes to searching for extraterrestrial intelligence (SETI), the tool of choice for the last fifty years has been a radio telescope, rather than an optical telescope. Almost 1,000 star systems have been scrutinized for "intelligent" radio signals using increasingly sophisticated phased-array antennas. The Allen Telescope Array (funded largely by Paul Allen, cofounder of Microsoft) in California currently has 42 dish antennas, each 6 m in diameter. It is eventually supposed to grow to 350 dishes, and should be able to observe one million star systems within a decade. View full abstract»

There is a limitation in the field of view (FOV) of large aperture radio telescopes, which is usually unavoidable. In order to enlarge the FOV, we may place several discrete feeds at the focal plane of the telescope. When all of the feeds work at the same time, we can achieve an FOV extended to several times, which equivalently increases the functions of the telescope. The disadvantage of this solution is the sparseness of the sampling at the FOV, which is not desirable for a continuous imaging process. Moreover, the number of the feeds mounted at the focus is restricted by the F/D (focal length to diameter) ratio of the telescope. We investigate an innovative technology to realize a simultaneous and continuous large FOV for the FAST (five-hundred-meter aperture spherical radio telescope). The new feed is proposed to be made of a focus array whose elements are microstrip antennas, so called Vivaldi antennas. An electromagnetic property of the Vivaldi element and the Vivaldi array is introduced, which is essential to the formation of the focus array. The focal field distribution (FFD) of the FAST for different illuminated portions is simulated using the GRASP8 software package. The results give critical information for the layout design of the focus array, especially the weighting system of the Vivaldi array. Cursory configurations of the array structure are suggested, and illumination patterns are estimated. Finally, some remarks on the feasibility of applying the Vivaldi array to FAST are made. View full abstract»

The field-of-view of a reflector-based radio telescope can be significantly increased by using phased array feeds (PAFs). Such PAFs need to be polarimetrically calibrated to allow proper reconstruction of the polarization state of the radio waves received. In this paper, we present far field radiation patterns of the Aperture Tile-in-Focus (APERTIF) system on the Westerbork Synthesis Radio Telescope (WSRT) obtained for polarimetric characterization of the instrument. We also demonstrate successful application of these calibration results by reconstructing the rotation measure towards BL Lac over a frequency range from 1190 to 1390 MHz. View full abstract»

The brighter radio sources and two regions of the Milky Way were surveyed at 440 mc with equipment mounted in the Naval Research Laboratory's 50-foot radio telescope. An attempt was made to keep the technique in this survey as similar as possible to that used at higher frequencies. Flux values are given for nine discrete sources and contour maps are presented for the section of the galactic plane near and north of the galactic center and for the area near the strong radio source, Cygnus A. The results obtained for five of the discrete sources and for two lines across the Milky Way are compared with the results of other observers at other frequencies, in an attempt to study the radio frequency spectra of astronomical objects. View full abstract»

An ultra-low noise single sideband SIS receiver has been prepared for radio astronomy at the sub millimeter wavelength /spl lambda//spl ap/0.85 mm. The minimum single sideband receiver noise temperature of 48 K corresponds to 3 h/spl omega//k or equivalent number of 3 photon of noise. The minimum single sideband SIS mixer noise temperature is about 20 K, close to 1.2 h/spl omega//k, or one photon of noise. The Nb/AlOx/Nb junctions with a Josephson critical current density of 9 KA/cm/sup 2/ and with the area of about 0.9 /spl mu/m/sup 2/ were used. The receiver has been tested at the 30 meter IRAM radio telescope in the winter seasons of 1997 and 1998. The observations at the radio telescope are speeded up by a factor of two to three with the new receiver. View full abstract»

We have three focal plane array receiver systems in the Nobeyama Radio Observatory 45-m radio telescope. These are S40M at 40 GHz, BEARS at 100 GHz, and NOBA at 150 GHz. A focal plane array receiver system at MM wavelengths is superior to a single receiver system in sensitivity and in the power of reducing atmospheric effects. The telescope and the array receivers cover the wide frequency range of the Rayleigh-Jeans region of the Sunyaev-Zel'dovich (S-Z) effect. The 45-m telescope is a most powerful tool for the observation of the S-Z effect. We have performed the ON-OFF observation of the S-Z effect toward eight X-ray bright galaxy clusters from z = 0.18 to 0.55 at 43 GHz as a pilot survey. The S-Z effects were detected for all clusters as a temperature decrement of 0.5-1 mK at the center. The Hubble constant is estimated to be H₀ = 64±17 km/s/Mpc for a flat ΛCDM cosmology, which shows good agreement with the values by other S-Z effect observations. The mapping observations of the S-Z effect are on-going. Although most of the observed images are roughly described by the isothermal spherical P-model density distribution, the deviation from the model seems to be large for clusters with an irregularity in the X-ray image rather than those without it. View full abstract»

We consider a problem of increasing the field of view (FOV) of the radio telescope by means of multi beam performance of the prime focus hybrid reflector systems. It was shown that array feeds of waveguide and horn elements currently used cannot provide closely spaced beams over a wide FOV and a high aperture efficiency in each beam due to the element spacing restrictions imposed by a size of the element aperture. We proposed a feed design in a form of an integrated dense array with a small physical size of the grid element and a volumetric form of the array element. For the feed, the original excitation system of the array elements has been developed to perform the desirable beam illumination pattern with low spillover level. The results have been obtained both for theoretical and experimental radiation patterns of the array feed. Scanning and multi beam capabilities and limitations of the hybrid reflector antenna have been investigated on the basis of the focal field distribution analysis. As an example, 0.35 F/D ratio reflector (Westerbork Telescope) has been considered. It has been shown that the proposed array antenna is a good candidate be used as the feed to improve the properties of source images by the reflector systems and therefore to increase the FOV of the radio telescope. View full abstract»

This paper presents a wideband low-noise amplifier (LNA) designed to be used as the first stage of the receiver in the Square Kilometer Array radio telescope. The LNA design procedure and its layout features are discussed. The noise figure optimization procedure determines the signal-source resistance that results in reduced noise figure. When used in the radio telescope, the required signal-source resistance will be presented by the telescope custom-made antenna elements. The LNA, designed in 90 nm bulk CMOS, achieves sub-0.2 dB noise figure from 800 MHz to 1400 MHz, return loss of more than 11 dB, gain of more than 17 dB driven into a 50 load, output 1 dB compression point of 2 dBm, output IP3 of 12 dBm, and output IP2 of 22 dBm while consuming 43 mA from a 1 V supply. In the LNA implementation presented in this paper the load choke inductor and the source inductor are integrated whereas the gate-, bias-, and the choke-inductor between two transistors of the cascode are external. The noise figure of the presented LNA is to our knowledge the lowest noise figure achieved by a power matched wideband CMOS LNA at room temperature. View full abstract»

A 3.5-km long interferometer consisting of the 530 by 30 m Ooty radio telescope, two 13.5-m diameter dishes, and a 5-m diameter dish are described. For generating coherent local-oscillator signals for the interferometer, a simple phase-stable radio link has been developed which uses the sum-frequency method proposed for the VLA antenna. The interferometer, expected to be in operation in 1973, will provide a resolution of about 0'.8×5'.5 arc at 327 MHz and will be able to detect a radio source of flux density 2 × 10^-28. Wċm^-2Hz^-1with a S/N ratio of 5 to 1. A proposed 10-km long synthesis interferometer consisting of the Ooty telescope and 36 dishes of 5-m diameter is also described. At 327 MHz, this instrument will provide beamwidths of 15" by 3" arc and 15" by 20" arc at declinations of 0° and 30°, respectively. It will have a sensitivity of about 10^-28Wċm^-2Hz^-1for a 9.5-h observing period. View full abstract»

We are developing the high sensitive 0.13- 0.38 THz radiometer for 6 m optical telescope BTA of SAO RAS with the purpose to add frequency operation points in corresponding atmosphere transparency windows to already existing operation frequencies in observation facilities of the Observatory from ultraviolet region - 3000 Angstroms at BTA till maximum wavelength - 0.5 m of the radio telescope RATAN-600 of SAO RAS. This will give the possibility to carry out wide range multifrequency investigations in one observatory what does not have an analogue in the world. Main functional radiometer parts: high sensitive receiving elements, receiving antenna array, optical elements which matching telescope from focal plane till receiving antenna array, signal multiplexing circuit and 0.3 K cryogenic system - are described briefly. View full abstract»

On radio telescope RT-2 mapping of the Sun is carried out by scanning of its image in right ascension α at various angles of declination δ. For a required angular resolution at. image reconstruction about 1' the registered image of the Sun in a square window in size 1°×1° should represent a matrix in size 64×64 an element. In the specified window time of obtaining of one scan makes value about minutes. Therefore time of obtaining of the full matrix size 64×64 an element exceeds 6 hours. This time is unacceptable for registration of nonstationary processes. In most cases sizes of active formations (AF) are comparable with achievable resolution that does not allow to restore their spatial structure. Nevertheless, restoring of AF allows to define such relevant arguments, as their angle sizes, coordinates and brightness temperature. These parameters can be received not only at detail mapping the Sun, but also on the basis of recovery single one-dimensional orthogonal scans areas of arrangement of AF. Presence of orthogonal scans of area from AF allows to execute a bearing of AF and to determine their spatial sizes and coordinates. Each of restored orthogonal cross-sections gives appropriate sizes of AF, their centers of gravity and integral brightness temperature. Orthogonal coordinates of the centers of gravity determine position of AF on the solar disk. The restored orthogonal sizes determine the greatest possible sizes of AF. The exactitude of a bearing and restoring of brightness temperature of AF depends on ratio of its angle sizes and width of directivity. diagram. of radio telescope, and also from angular distance between orthogonal sections and the real standing of AF. View full abstract»

The Kiwi Advanced Research and Education Network (KAREN) has been used to transfer large volumes of radio astronomical data between the Radio Astronomical Observatory at Warkworth, New Zealand and various international organizations involved in joint projects and VLBI observations. Here we report on the current status of connectivity and on the results of testing different data transfer protocols. We investigate new UDP protocols such as `tsunami' and UDT and demonstrate that the UDT protocol is more efficient than `tsunami' and `ftp'. We also report on tests of direct data streaming from the radio telescope receiving system to a correlation centre without intermediate buffering or recording (real-time eVLBI). View full abstract»

The center-to-limb brightness distribution of the sun at radio wavelengths gives information about the structure of the solar atmosphere. Radio telescopes have poor spatial resolution, however, and cannot provide detailed angular measurements of the brightness distribution. During a solar eclipse, the sharp edge of the moon can be used to greatly increase the angular resolution of the radio telescope in one dimension. This paper describes the technique used to estimate the brightness distribution at 3.3 mm wavelength of the solar limb from measurements made during a total eclipse. The outer edge of the sun is divided into thin concentric bands and parameteric estimation methods are used to estimate the average flux desity of each band. This approach has several advantages for inverting radiometric data, especially in scanning problems. View full abstract»

Measurements of the difference between radio and optical astronomical refraction atlambda=8.6, 4.3, 3.1, and 2.2 mm are described. The measurement technique utilized solar limb crossing times observed with a 16-foot radio telescope. Results show the expected dependence upon atmospheric water vapor belowlambda= 3mm, but radio refraction tends to approach optical refraction at the shortest wavelength. View full abstract»

We have developed a fixed-tuned SIS (superconductor-insulator-superconductor) mixer across 120-180 GHz band. This mixer employs an SIS chip fabricated by Nobeyama radio observatory which consists of a series array of 6 Nb/Al-Al₂O₃/Nb junctions in a microstrip line on a fused quartz substrate. The SIS chip is placed at the center of the half-height waveguide mixer mount to have a good incoming signal coupling over the whole frequency band. No mechanical tuner was used in the SIS mixer and the RF signal and local oscillator power are injected to the mixer via a cooled cross-guide coupler. We measured double sideband noise temperatures of a receiver using the SIS mixer, which is 32-131 K over 120-180 GHz band. The developed SIS mixer is now in use for radio astronomical observations on the TRAO 14-m radio telescope. View full abstract»

Phased Array Feeds (PAFs) for large diameter single dish radio telescopes offer the capability for multiple simultaneous beam formation and wide field-of-view surveys. An L-band PAF front end design is presented for the Five-hundred-meter Aperture Spherical Telescope (FAST), which is currently under construction and when complete will be the largest single dish radio telescope in the world. A broadband PAF element at L-band was designed in conjunction with the FAST optics and focal plane field distribution, fabricated, and tested. The simulated performance of the array meets the FAST PAF performance requirements for field of view, efficiency, sensitivity, and other key parameters. A unique aspect of the FAST PAF is the need for feed cabin vibration compensation. A study of the use of adaptive beamforming to compensate for lateral movement is given. View full abstract»

The problem of increase of radio-telescope (RT) use efficiency in mm radiowaves range at supervision of the removed cosmic radio-sources (RCR) is considered. The problem consists that at pointing RT dishes system (DS) on RCR arise not compensated DS elements deformations. It results in distortion of distribution electromagnetic (EM) fields on an input of radio receiver (RR). The technique of restoration of true EM field distribution is offered by row scanning of some space area in which the finding of observable object is supposed. View full abstract»

This paper presents the analysis results (in terms of settling time, bandwidth, and servo error in wind disturbances) of four control systems designed for the Large Millimeter Telescope (LMT). The first system, called PP, consists of the proportional and integral (PI) controllers in the rate and position loops, and is widely used in the antenna and radio telescope industry. The analysis shows that the PP control system's performance is remarkably good when compared to similar control systems applied to typical antennas. This performance is achieved because the LMT structure is exceptionally rigid; however, it does not meet the stringent LMT pointing requirements. The second system, called PL, consists of the PI controller in the rate loop, and the linear-quadratic-Gaussian (LQG) controller in the position loop. This type of controller is implemented in the NASA Deep Space Network antennas, where pointing accuracy is twice that of the PP control system. The third system, called LP, consists of the LQG controller in the rate loop, and the proportional-integral-derivative (PID) controller in the position loop. This type of loop has not been yet implemented at known antennas or radio telescopes, but the analysis shows that its pointing accuracy is the ten times better than the PP control system. The fourth system, called LL, consists of the LQG controller in both the rate loop and the position loop. It is the best of the four, with accuracy 250 times better than the PP system. It is thus worth further investigation to identify implementation challenges for telescopes with high pointing requirements. View full abstract»

The Low Frequency Array (LOFAR) is the largest telescope in the world operating at a frequency range from 30 to 240 MHz. LOFAR is the first radio telescope of its size which uses phased array principles to detect radio signals. More than 10,000 antennas are installed in the field. The antennas are grouped in 44 stations. The maximal distance between the stations is about 1500 km resulting in a tremendous spatial resolution. In this paper the LOFAR system architecture is discussed and the status is described. View full abstract»

This study presents the design and experimental results of a wide-band passive antenna-feed system developed for the C-band dual-circular-polarisation receiver of the Sardinia radio telescope (SRT). The latter is a 64 m diameter shaped radio-telescope under construction designed to operate with high efficiency from 300 MHz to over 100 GHz. The developed C-band antenna-feed system exhibits very high performances in a 30 band centred at 6.7 GHz, for example the return loss at all electrical ports is higher than 30 dB and the cross-coupling between the two polarisations is lower than 34 dB. The design solutions of all the feed-system components such as marker injector, polariser, transitions and the ortho-mode transducer (OMT) are reported in the study. In particular, the novel architecture of the OMT that provides an isolation between the two rectangular ports better than 70 dB is described in close detail. Computed and experimental results regarding both the complete system and its sub-assemblies are reported and discussed. View full abstract»

Primary beam shapes are emerging as a vital consideration both in the calibration of the new generation of radio interferometers, and in the design of future instruments such as the SKA. However, their impact on interferometer performance is far from obvious, especially since calibration techniques addressing these effects are still in their relative infancy. We present the results of recent work aimed at developing a comprehensive interferometric simulations methodology which can be used to quantify the impact of beamshapes on radio interferometer sensitivity. We show the results of applying this methodology to a comparative study of several possible MeerKAT dish designs. In particular, two beamshape-related effects that have been virtually ignored in older (lower-sensitivity) telescopes are far sidelobe confusion noise (FSCN), and calibration artefacts due to pointing errors (PEs). These effects are quite subtle and often completely non-intuitive, so exploring them via simulations can lead to interesting new insights into radio telescope design. View full abstract»

This letter reports on our recent improvements in photomixing technology for the realization of a photonic local oscillator (LO) at 1.05 THz for the Atacama Pathfinder Experiment (APEX) radio telescope. Experiments with state-of-the-art photomixers, operated at room temperature and in cryogenic environment demonstrate successful operation of an astronomical heterodyne receiver at 1050 GHz with a superconductor-insulator-superconductor (SIS) mixer. The system noise temperature of the heterodyne receiver pumped by the photonic LO was at least as low as that using a conventional solid-state LO in the same receiver system. An optical comb generator served as a relative frequency reference to which both lasers were phase-locked. Under the phase lock condition, the 3 dB linewidth of the THz signal was below 3 kHz and could be continuously tuned within a range of 500 MHz-the overall tunability of the system was determined by the photomixer antenna resonance bandwidth, which was roughly 200 GHz. We installed the laser system in the telescope pedestal, from there, the frequency-stabilized laser signal, was fed into the photomixer, installed in the Nasmyth cabin of the telescope, through a 20 meters long single-mode fiber optic. View full abstract»

Grote Reber, amateur radio operator W9GFZ, died December 20, 2002 in Tasmania. He would have been 91 years old on December 22nd. Reber is acknowledged as the Father of Radio Astronomy and the inventor of the first true radio telescope. With the advent of space satellites, his greatest legacy may well be his invention of the parabolic dish, designed to receive nonterrestrial electromagnetic radiation, a concept that has revolutionized worldwide communication. View full abstract»

Gigahertz-frequency phased arrays that are integral to next-generation radio astronomy instruments, in particular the Square Kilometre Array (SKA) radio telescope, pose a significant signal processing challenge. We argue that the development of high-performance signal processing systems is critical, not only for the particular application to future radio astronomy instrumentation, but also to the entire field of ultra-wideband phased arrays in the gigahertz bandwidth range. To this end, we have developed a cycle-accurate simulator environment and programming language for a novel, massively multicore array processor, and prototyped on it representative digital frequency domain algorithms. The results of this analysis reveal beamforming as a low compute-to-I/O processing task, best suited to high-I/O-bandwidth, streaming signal processing systems. View full abstract»

Radio Frequency Interference (RFI) is a very important issue to address in order to setup a radio astronomical facility. We have successfully done the site testing on some important and strategic places in Malaysia and we present the results in this paper. We will implement the usage of the Spectral Kurtosis (SK) estimator in order to eliminate the RFI. In this paper, we present the results of the 3-D and basic statistical Kurtosis analysis method that we have applied to our RFI data. We have found that this method allows us to conclude the RFI level at the individual sites without having to look at the graphs of the frequency spectra. In this paper, we will also discuss the possibilities of the planned science goals that can be done with the future radio telescope facility in Malaysia, including studies in cosmology and space weather. View full abstract»

Large phased arrays have received great attention in recent years as the high resolution antennas become in increasing demand. More recently the Advisory Panel of Radio Telescopes of the National Science Foundation[1] has adopted the resolutions on the need of a decimeter radio telescope with a 1' of arc beam. A preliminary study for the Benelux project[2] also considered a few antenna arrays for Mills-Cross type telescope. Motivated by such activities the present investigation was made in an attempt to develop a new technique in the design of high resolution antenna arrays. View full abstract»

Future ultra-wideband (UWB) radio telescopes require UWB feeds for reflector antennas, and many new UWB feed technologies have gained substantial progress to satisfy the tough specifications for future radio telescope projects, such as the square kilometer array (SKA). It has been noticed that, different from traditional narrow-band horn feeds, all UWB feeds are non-BOR (Body of Revolution) antennas. Therefore, BOR1 efficiency becomes an important characterization for the modern UWB feed technologies. We present a novel circular Eleven feed, constructed of “circularly” curved folded dipoles printed on flat circuit boards, in order to have high BOR1 efficiency at a low manufacture cost. The Genetic Algorithm (GA) optimization scheme has been applied to the design for achieving a low reflection coefficient. Simulated and measured results show that the circular Eleven feed has a reflection coefficient below -6 dB over 1.6–14 GHz and below -10 dB over 78% of the band, and an aperture efficiency higher than 60% over 1–10 GHz and 50% up to 14 GHz. View full abstract»

MeerKAT is spearheading the development of a number of radio astronomy instrumentation techniques. This 64-dish array will feature direct digitisation of the sky signal with no analogue downmixing and a heterogeneous, realtime signal processor employing a commercial Ethernet network for all inter-device communications. By investing in portable intellectual property rather than hardware, the engineering team is able to deploy instrumentation on new hardware quickly and so leverage the latest technologies. This shrinks the system size, lowers costs and power consumption and increases system capabilities. This digital processor will make MeerKAT a highly flexible radio telescope, able to adapt to changing science requirements quickly and efficiently. View full abstract»

An instrument that has been developed for measuring the deformations in shape that result from the movement of a radio telescope reflector is described. A radar technique is used to measure distances from near the focal point of the reflector to selected points on the reflector surface. The short term accuracy of the instrument is ±0.003 in) and when used on the 140-ft telescope in Green Bank, W.Va., good agreement was found between calculated and measured deformations. View full abstract»

We have already developed a low-noise 100 GHz band (98-115 GHz) SIS mixer using Nb/AlOx/Nb junction technology. The mixer has a noise temperature of 17 K when used as a double sideband (DSB) heterodyne receiver. The SIS receiver has been in use in the 4 m radio telescope at Nagoya University for five years. As a further application of the SIS mixer, we developed middle-atmosphere ozone monitoring system using an SIS mixer for the first time. The system can measure ozone mixing ratio every 5 minutes. The integration time is less than 1/10 of the time needed in a conventional system using Schottky barrier diode (SBD) mixers. We have also begun developing developing a 200 GHz band (210-280 GHz) SIS mixer for radio astronomy and for monitoring other minor constituents such as ClO. The preliminary experiment showed that the mixer has a rather low noise temperature of 60 K (DSB).<> View full abstract»

The Square Kilometre Array project will soon decide upon where this new large radio telescope will be located, on the basis of a range of criteria. Two environmental aspects are examined for maximum scientific return through measurements at candidate sites: the radio frequency interference (RFI) and tropospheric environments. High sensitivity as well as high speed measurements will make an inventory of the RFI at the core sites and at a selection of remote sites. Tropospheric phase stability will be investigated using two identical interferometer systems pointed to geostationary satellites, in a campaign lasting at least one year. A report. View full abstract»

A specially constructed combined radio telescope-radio sextant has provided continuous measurement of the power from the sun. The change in received power with zenith angle has been used to estimate the attenuation due to the atmosphere at the wavelength of 8.7 mm. Values ranging from 0.031 to 0.067 db per km at sea level were observed for days with a wide variety of weather conditions. Qualitative statements concerning attenuation under conditions of unusually heavy rainfall are made. View full abstract»

As radio astronomers become increasingly interested in observing at millimeter and submillimeter wave lengths, the need arises for the measuring and setting of the surface shape of parabolic reflectors to a higher accuracy than is obtainable using conventional techniques. Typically the accuracy required is greater than 0.1mm. The method described in this paper measures the curvature of the surface with a high accuracy at many points along a radius of the surface. These curvature values are then integrated twice with respect to the distance along the surface by an on-line computer, the result being the Y coordinate of the surface as a function of distance along the radius. This measurement is repeated for different radii, the resultant data being used to generate the best fit parabola to the surface and deviations from this best fit. Measurements made on an 11 meter radio telescope yield results for the RMS surface accuracy that are consistent with the antennas measured performance at millimeter wavelengths. Two separate measurements of the same surface indicate a measurement accuracy of 0.05mm RMS. The time taken to survey the 11 meter antenna was less than 4 hours for 48 radii and greater than3 times 10^{5}data points. View full abstract»

This paper describes the realization of the design of a cryogenically cooled, low noise, Focal Plane Array, for radio astronomy applications. The system is required to be mounted at the focus of a large parabolic reflector, and perform astronomical measurements in the range 4 GHz to 8 GHz. It allows simultaneous observations with four steerable beams. Surveying and imaging speed of a radio telescope depends on the number of beams creating the field of view. High quality observations require efficient reflector illumination and low-noise temperature of the receiver. The beams are formed by analogue techniques, with minimal power, computing, interference and connectivity overheads. The focus of this paper is on the front end design implementation of the low noise amplifiers, beam forming modules and overall system integration. View full abstract»

A 500-m aperture spherical telescope (FAST) was funded by the National Development and Reform Commission of China (NDRC) in July 2007 and will be located in the unique Karst region, a sinkhole-like landform, in Guizhou province. FAST can be seen as a modified ldquoArecibordquo type radio telescope using many innovative techniques, with as much as twice the collecting area and a wider sky coverage. FAST has, first, an active reflector, conforming to a paraboloid of revolution from a sphere in real time through actuated control, which enables the realization of wide bandwidth and full polarization capability by using standard feed design. Secondly, it has a light focus cabin suspension system, integrating optical, mechanical, and electronic technologies, reducing effectively the cost of the support structure and control system. With such a huge collecting area of more than 30 football fields, FAST will become the largest single dish ever built. Here we will summarize the FAST concept and the milestones achieved in experiments on its key technologies, i.e., site exploration, active reflector prototyping, focus cabin driving mechanism, measurement and control techniques, and the receiver layout. The Miyun FAST demonstrator also will be presented. View full abstract»

A general survey of the principles of radio astronomy receivers is presented. System noise temperature, the sensitivity of different receiver types, and the calibration of receivers are studied. A total-power receiver is analyzed as a basic radio telescope receiver and. the results are used to obtain the performance of other receiver types such as the Dicke receiver, Graham's receiver, correlation receiver, and phase-switching receiver. View full abstract»

LOFAR, the Low Frequency Array, is a next generation radio telescope designed by ASTRON, with antenna stations located in the north of the Netherlands and across Europe. A total of 40 LOFAR stations are nearing completion in the Netherlands; the closest ones in the core area are nearly adjacent, and they then range up to distances of 80 km. A further 8 international stations are being deployed in Germany, France, Sweden, and the UK, on distances up to 1000 km. Plans for more LOFAR stations exist in several other countries in Europe. Utilizing a novel, phased-array design, LOFAR is optimized for the largely unexplored low frequency range between 30 and 240 MHz. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescopes as well as the potential for multiple simultaneous observations. Processing (e.g. cross-correlation) of the station data takes place in the LOFAR BlueGene/P supercomputer, and associated post-processing facilities. With its dense core array and long interferometric baselines, LOFAR is gearing up to reach unparalleled sensitivity and spatial resolution in the low frequency radio regime. In this paper, we will summarize both some of the most recent data calibration achievements, and some of the exciting astronomical results that are being produced at an accelerating pace in recent weeks and months, as the observatory is gearing up for survey-style operations in the upcoming winter season. View full abstract»

The cooperative variation of lengths of the six long cables pulls the feed cabin to track some radio source with six-DOF. Similar to a parallel manipulator, the cable-cabin flexible structure for the new generation large spherical radio telescope is viewed as a cable-supported parallel manipulator (CPM). Due to the inherent characteristics of nonlinearity, large delay and multivariable coupled flexible structure, a novel control method combining sliding mode control and fuzzy logic control is developed to realize the trajectory tracking of the feed. The approach applies fuzzy controller to adjust the parameters of reach law of sliding mode timely. At the same time the exponent approximating control is added by grading. This approach not only ensures the speediness and robustness of the control system, but also can weaken chattering. In addition, on the basis of embedded system design method, the servo controller for CPM is designed. The design of the control system is simple and it can be easily applied in the engineering. The simulation results show that the effectiveness of the proposed method View full abstract»

The author discusses two Bachelor Engineering degree projects in the field of radioastronomy. The first is the design, construction and, hopefully, the operation of a radio telescope to receive signals from the Sun. The other is a similar exercise where the objective is to detect solar flares by an indirect radio method. Both topics are too extensive for any one student to tackle successfully in the time available. The requirement that each of them work on an individual project would be satisfied easily by the multidisciplinary nature of the topics. No two students would work on the same problem. However, all the hardware and software they produced would have to interface with the other elements of the system developed by their colleagues View full abstract»

The global radio astronomy community has for the last several years embarked on an exciting project known as Square Kilometer Array (SKA). This project is a radio telescope operational from 0.1GHz to 25GHz, with a square kilometer of overall collecting area, providing an increase in sensitivity of two orders of magnitude. To meet this wideband requirement, many national institutes have proposed various concepts, some of which will be reviewed in this paper. View full abstract»

The ALMA Radio Telescope has a large, integrated, software system to handle all aspects of telescope operation. This software has been developed by a large international consortium of collaborating institutions. This paper briefly describes the scope of the software effort, the technical approach which has been implemented, and the management approach which has been used to oversee its development. View full abstract»