New design of large fully-steerable radio telescope reflector based on homogenized mesh structure

The self-weight of a large fully-steerable radio telescope is one of the important factors affecting its performance. In the existing reflector system scheme, the problem of surface accuracy caused by its large and heavy structure has seriously restricted the application and implementation of large radio telescopes.Therefore, a new mesh structure scheme for a large fully-steerable radio telescope reflector is proposed in this paper. This scheme is based on a homogenized mesh back-up structure in the form of a quasi-geodesic grid and regular quasi-tri-prism or tetrahedron, which can significantly reduce the structural complexity and self-weight of the reflector under the condition that the reflector can meet the desired performance requirements. Finally, the feasibility and rationality of the scheme are evaluated by numerical simulation analysis, which has significant advantages and provides a new design for the reflector of a large fullysteerable radio telescope.     

Non-uniform temperature distribution of the main reflector of a large radio telescope under solar radiation

The non-uniform temperature distribution of the main reflector of a large radio telescope may cause serious deformation of the main reflector,which will dramati...     

Research on the panel adjustment method of an active main reflector for a large radio telescope

The surface accuracy of a large parabolic antenna is an important indicator to evaluate the quality of the antenna.It not only directly affects the antenna’s aperture efficiency,thereby determining the shortest wavelength that the antenna can work,but also affects the main lobe width and side lobe structure of the antenna pattern.Microwave holography is an important method for parabolic antenna profile detection.In this article we adopt a new algorithm to adjust the panels for the large radio telescope with an active main reflector through the TM65 m antenna’s aperture phase profile.The panels of the TM65 m radio telescope is in a radial pattern with 14 rings.Each corner of the panel is fixed on the screw of the actuator to move up and down,and the adjacent corners of the four panels share an actuator.We use the method of plane fitting to calculate the adjustment value of every panel’s corner.But one actuator,which simultaneously controls the common corner of the adjacent panels,will have different adjustment values according to the different plane fitting equation based on adjacent panels.In this paper,the adjustment value of the adjacent panels’crosspoints are constrained to be equal to the constraint condition to calculate each actuator’s adjustment value of the TM65 m radio telescope.Through multiple adjustments and application of the new algorithms,the accuracy of the TM65 m antenna reflector profile has been improved from the original 0.28 mm to the current 0.19 mm.     

A novel design for a giant Arecibo-type spherical radio telescope with an active main reflector

A novel design for a giant spherical radio telescope is proposed. Instead of a fixed spherical reflecting surface such as with the 305-m Arecibo telescope, the illuminated portion of the reflecting surface is made to fit a paraboloid of revolution in real time by active control. A simple feed can thus be used, enabling the realization of broad bandwidth and full polarization. The actual design utilizes a karst depression which gives a spherical surface of 300-m radius, having an opening of 500-m diameter. The illuminated aperture is chosen to be 300 m, and the focal ratio is 0.46–0.48. With this geometry and the simple feeding system, a giant telescope with large sky coverage can be achieved at low cost. When the illuminated aperture is limited to 70–100 m, the area trackable can be extended to about 10° above the horizon.     

Effect of the alidade thermal behavior on the pointing accuracy of a large radio telescope

The alidade's non-uniform temperature field of a large radio telescope is very obvious under solar radiation. Estimating a radio telescope's pointing errors, caused by the alidade deformation under solar radiation, is significant to improve the telescope's pointing accuracy. To study the effect of the alidade thermal behavior on the pointing accuracy of a large radio telescope, a temperature experiment is first carried out in a 70-m radio telescope on a sunny day. According to the measured results, the temperature distribution rule of the alidade is summarized initially. In addition, the alidade's temperature field is calculated by finite element thermal analysis. The simulated results are proved to be in good agreement with the experimental results. Finally, the alidade deformation under solar radiation is computed by finite element thermalstructure coupling analysis. The telescope's pointing errors caused by alidade deformation are estimated via the alidade's node displacements. The final results show that the effect of alidade thermal behavior on the telescope's elevation pointing errors ?ε_2 + ?ε_r is much more than the effect on the telescope's crosselevation pointing errors ?ε_1. The maximum of ?ε_2 + ?ε_r is more than 45, while the maximum of ?ε_1 is less than 6. This study can provide valuable references for improving the pointing accuracy of large radio telescopes.     

Spectroscopic research with the Hartebeesthoek radio telescope

Research into star-forming regions, evolved HII regions, late-type stars with circumstellar dust shells and comet Halley using spectroscopic observations made with the Hartebeesthoek radio telescope is reviewed.     

Dwingeloo – the golden radio telescope

The Dwingeloo 25‐m telesope, inaugurated in 1956, has played a major role in research for half a century. We trace its history back to its conception in 1944, and summarize its main achievements. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The optical reflector system for the CANGAROO-II imaging atmospheric Cherenkov telescope

A new imaging atmospheric Cherenkov telescope with a light-weight reflector has been constructed. Light, robust, and durable mirror facets of containing carbon fiber reinforced plastic laminates were developed for the telescope. The reflector has a parabolic shape (f/1.1) with a 30 m² surface area, which consists of 60 spherical mirror facets. The image size of each mirror facet is 0°.08 (FWHM) on average. The attitude of each facet can be adjusted by stepping motors. After the first in situ adjustment, a point image of about 0°.14 (FWHM) over 3° field of view was obtained. The effect of gravitational load on the optical system was confirmed to be negligible at the focal plane. The telescope has been in operation with an energy threshold for γ-rays of 300 GeV since May 1999.     

A digital correlation receiver for the GEETEE radio telescope

A 128-channel digital correlation receiver has been built for the GEETEE 1, the low-frequency radio telescope situated at Gauribidanur, South India, (latitude 13°36′12′′ N). The receiver uses a modified doublesideband (DSB) technique. The quadrature samples required for a DSB system are obtained by sampling the digitized intermediate frequency (I.F.) signals by two clocks which are separated in time by one quarter of the period of the I.F. The visibilities required for one-dimensional synthesis are measured using one-bit correlators. A technique to measure amplitude information for the signal using a threshold detector and a one-bit correlator has been developed. The receiver has been successfully used for continuum, spectral-line and pulsar observations. The antenna system of GEETEE and its configuration for one dimensional synthesis are also described in this paper This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore and the Raman Research Institute, Bangalore.     

A new spectrum analyzer for radio astronomical studies with the radio telescope RATAN-600

The spectral measuring facility with a new Fourier analyzer for use with the radio telescope RATAN-600 is described and its experimental data are reported.     

Modeling the rail surface unevenness of a high-precision radio telescope

This study proposed a coarse-fine mixed model for describing the rail surface unevenness of an ultra-large fully steerable radio telescope(Qi Tai Telescope) with a diameter of 110 meters. The rail surface unevenness includes information on error arising from two different scales, i.e., the long-periodshort-change and the short-period-long-change. Consequently, in this study an idea of a mixed model was proposed, in which trigonometric and fractal functions were, respectively, used to describe information on error from two scales. Key parameters were determined by using the least squares method and the wavelet transform method, and finally, a specific mathematical expression of the model was obtained by optimization. To validate the effectiveness of the new modeling method, the mixed model was then used to describe the rails of the Green Bank Telescope, the Large Millimeter Telescope, and a radio telescope in Miyun, Beijing. A comparative study revealed that the maximum error was less than15%, thus the result was superior to those of existing modeling methods.     

Detection, excision and statistics of interference at the Mauritius radio telescope

A technique to detect man-made interference in the visibility data of the Mauritius Radio Telescope (MRT) has been developed. This technique is based on the understanding that the interference is generally ‘spiky’ in nature and has Fourier components beyond the maximum frequency which can arise from the radio sky and can therefore be identified. We take the sum of magnitudes of visibilities on all the baselines measured at a given time to improve detectability. This is then high-pass filtered to get a time series from which the contribution of the sky is removed. Interference is detected in the high-pass data using an iterative scheme. In each iteration, interference with amplitudes beyond a certain threshold is detected. These points are then removed from the original time series and the resulting data are high-pass filtered and the process repeated. We have also studied the statistics of the strength, numbers, time of occurrence and duration of the interference at the MRT. The statistics indicate that most often the interference excision can be carried out while post-integrating the visibilities by giving a zero weight to the interference points.     

Analysis for reflector aluminum mesh panels of five-hundred meter aperture spherical telescope

In this paper, an analysis of the aluminum reflector mesh panels for the Five-hundred meter Aperture Spherical Telescope (FAST) is described. The study concentrates on one element of the reflector surface with the shape of a triangle. For the analysis, the panel is modelled as a mesh of cables so that it can be treated as continuous. It is demonstrated that the results so obtained are reasonable. This revised version was published online in July 2006 with corrections to the Cover Date.     

Antenna design and implementation for the future space Ultra-Long wavelength radio telescope

In radio astronomy, the Ultra-Long Wavelengths (ULW) regime of longer than 10 m (frequencies below 30 MHz), remains the last virtually unexplored window of the celestial electromagnetic spectrum. The strength of the science case for extending radio astronomy into the ULW window is growing. However, the opaqueness of the Earth’s ionosphere makes ULW observations by ground-based facilities practically impossible. Furthermore, the ULW spectrum is full of anthropogenic radio frequency interference (RFI). The only radical solution for both problems is in placing an ULW astronomy facility in space. We present a concept of a key element of a space-borne ULW array facility, an antenna that addresses radio astronomical specifications. A tripole–type antenna and amplifier are analysed as a solution for ULW implementation. A receiver system with a low power dissipation is discussed as well. The active antenna is optimized to operate at the noise level defined by the celestial emission in the frequency band 1 ? 30 MHz. Field experiments with a prototype tripole antenna enabled estimates of the system noise temperature. They indicated that the proposed concept meets the requirements of a space-borne ULW array facility.     

Research on actuator distribution and panels for a radio telescope

Trying to achieve the best surface accuracy control with the fewest actuators, this article mainly studies the distribution of actuators and the method of panel design. The influence of the number of faulty actuators on the accuracy of the surface shape is demonstrated. In addition, the method incorporating a triangular panel, node index and the fitting solution method of a single panel is also given. This method provides a reference for the design and realization of an active surface or a deformable sub-reflector for high performance large aperture radio telescopes.