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Design and implementation of a low-noise prime-focus S/X receiver system for radio astronomy
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| Pengarang | : | R.D. Norrod |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 768-775 |
| Abstrak | : | This paper discusses the design, construction, and measured performance of dual-band, dual-polarization, prime focus receiver systems used on three antennas at the NRAO facility in Green Bank, WV. The receivers operate at Sand X-bands near 2.3 and 8.4 GHz. Described is the development of a new dualband feed horn, a cryogenics package with waveguide input ports using HEMT low-noise amplifiers, and a receiver system using optical fiber microwave links to transmit frequency reference and IF signals. Measured performance of major components and the overall installed system is given. |
Reduction of ground spillover in the Owens Valley 5.5-m telescope
| Pengarang | : | C.R. Lawrence |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 763-767 |
| Abstrak | : | The 5.5-m telescope of the Owens Valley Radio Observatory is used for highly sensitive measurements of the cosmic microwave background radiation, which are easily contaminated by ground spillover. The authors describe the modifications made to the secondary mirror support structure that reduced the total ground pickup of the antenna from 27 to 9 K and decreased the peak differential ground pickup for the observing technique from 43 mK to 140 /spl mu/K. This was achieved by reducing the physical obstruction, arranging the support leg angles to minimize direct reflections, and installing radiation baffles to control the direction of the reflection or scatter lobes. |
Design and implementation of an error-compensating subreflector for the NRAO 12-m radio telescope
| Pengarang | : | C.E. Mayer |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 756-762 |
| Abstrak | : | Describes the measurement of the surface shape of the primary reflector of the NRAO 12-m radio telescope and the use of the measurements to machine the shape of a secondary mirror to compensate for the primary reflector errors. The method known as holography was used with the 38.04-GHz transmitter on the geosynchronous Lincoln Experimental Satellite to map the main reflector. The machining of the secondary compensated for the errors in the primary shape, and as a result, at 345 GHz, the axial gain of the instrument was increased by about 50% and the antenna pattern correspondingly improved. |
Upgrading the Haystack radio telescope for operation at 115 GHz
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 742-755 |
| Abstrak | : | The Haystack 37-m radio telescope has been upgraded for operation at frequencies up to 115 GHz. A unique deformable subreflector with active actuator control has been developed to correct for gravitational distortion effects including astigmatism and deflections associated with the particular reflector surface. Active thermal compensation of the surface has also been implemented to conduct for both thermal lag effects and circularly symmetric gravitational deviations. Holographic mapping of the antenna surface deviations was achieved using 12-GHz geostationary satellite transmissions, which required the use of special techniques to correct for diffraction and multiple reflection effects involving the space-frame radome that covers the antenna. Realignment of the antenna surface utilized a finite-element structural model to translate surface deviations to motions of the unusual adjustment mechanisms on the antenna. The currently measured rms surface deviation (Dec. 23, 1992) is 210 /spl mu/m. The telescope has been equipped with a two-channel cryogenically cooled 3-mm SIS receiver, covering the range from 84 to 115 GHz. A new flexible digital spectrometer has been constructed for spectral line astronomy. Configurations can range from a widest bandwidth coverage of 160 MHz at 512 lags to 0.66 MHz at 4096 lags. Examples are given of surface holographic maps and radio measurements of aperture efficiency, pointing, and other performance parameters. |
Upgrade of a large millimeter-wavelength radio telescope for improved performance at 115 GHz
| Pengarang | : | M.J. Brenner |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 734-741 |
| Abstrak | : | A 20.1-m-diameter radome enclosed radio telescope, built by Electronic Space Systems Corporation (ESSCO) at the Onsala Space Observatory (OSO) near Gothenberg, Sweden, in 1975, was upgraded by ESSCO in 1992 for improved operation at 115 GHz, increasing the system aperture efficiency from 20% to 40% at this higher frequency. Electrical gain measurements confirm geometric optics predictions of efficiency and improved antenna patterns. The upgrade included replacement of the two inner reflector panel rows with 31-/spl mu/m panels, stiffening the reflector backstructure based on finite-element structural analysis for a measured rms gravity deformation of 59 /spl mu/m in the 25/spl deg/ to 70/spl deg/ elevation range, and optical alignment of the reflector surface to 58 /spl mu/m rms accuracy. This alignment accuracy of approximately 1/345000 of the reflector diameter was accomplished with an electronic angle-measuring theodolite and digital radial strap gauges. Data were downloaded in real time to an on-line portable computer performing surface metrology calculations. Graphical data are presented that compare computer predictions of reflector backstructure gravity deformations to optical measurements, which proved crucial in achieving the stringent alignment accuracies. Measured antenna efficiency data before and after the upgrade are included. |
A 45-m telescope with a surface accuracy of 65 /spl mu/m
| Pengarang | : | N. Ukita |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 725-733 |
| Abstrak | : | The Nobeyama 45-m telescope has been upgraded for higher frequency and higher sensitivity observations. The surface accuracy of the antenna was improved from 0.2 mm rms to 65 /spl mu/m rms using a radio holography method at the prime focus. Pointing accuracy was also improved by replacing a large Gregorian subreflector cabin with a smaller cassegrain subreflector in 1985 to reduce wind loading effects, and by installation of a new master collimator with multi-pole resolvers which were calibrated to an accuracy of 0.4 arcsec rms in 1988. Four SIS receivers using Nb/AlO/sub x//Nb array junctions are now available on the telescope for 40, 80, 100, and 150-GHz bands. These receivers achieved quite low noise and wide-band tunability. The 2/spl times/2 multi-beam receiver for 115 GHz is very powerful for mapping observations. These improvements of telescope performance and these receivers have significantly increased the astronomical observation capability of the telescope in the wide frequency range of 40 to 150 GHz. |
The Arecibo upgrading: electrical design and expected performance of the dual-reflector feed system
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 714-724 |
| Abstrak | : | The paper describes the electrical design and predicted performance of a dual-reflector feed for the fixed spherical reflector of the Arecibo radio telescope. This dual-reflector feed, dubbed the Gregorian has much larger bandwidth, lower losses, and provides better aperture illumination than the old line feeds. The paper begins with a historical review of the line feeds and the first conceptual designs of the dual-reflector feed. Following is a description of the mini-Gregorian, a small test version of the dual-reflector feed concept which is in use on the Arecibo telescope. The selection of an optimized geometry for the full-size Gregorian is detailed. The primary feeds must be a practical size at lower frequencies, the selected /spl plusmn/60/spl deg/ illumination angle from the focal point provides this attribute. The main body of the paper describes the expected performance of the final Gregorian design in the frequency range of 250 MHz to 8 GHz. The high-frequency performance is limited by the surface tolerance of the spherical main reflector and the alignment tolerances of the Gregorian feed. The latter effects are simulated and discussed. The low-frequency performance is limited by edge diffraction on both reflectors and by an unusual diffraction effect created by a very nonuniform field distribution near the center of the larger feed reflector. At low frequencies the exit pupil of the surrounding enclosure blocks some of the edge diffracted fields. This blockage causes extra losses and potential multi-path problems, problems which are both discussed. A cluster of seven feed horns providing multiple beams at 1.42 GHz is discussed. |
The Nobeyama radioheliograph
| Pengarang | : | H. Nakajima |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 705-713 |
| Abstrak | : | A new 17-GHz radio interferometer dedicated for solar observations was constructed in two years at Nobeyama, Nagano. It consists of eighty-four 80-cm-diameter antennas arranged in a tee-shaped array extending 490 m in east-west and 220 m in north-south directions. Since late June of 1992, radio full-disk images of the Sun have been observed for 8 h every day. The spatial resolution is 10" and the temporal resolution is 1 s and also 50 ms for selected events. Every 10 s correlator data are synthesized into images in real time and displayed on a monitor screen. The array configuration is optimized to observe the whole Sun with high spatial and temporal resolution and a high dynamic range of images. Image quality of better than 20 dB is realized by incorporation of technical advances in hardware and software, such as (1) low-loss phase-stable optical-fiber cables for local reference signal and IF signals, (2) newly developed phase-stable local oscillators, (3) custom CMOS gate-array LSTs of 1-b quadraphase correlators for 4/spl times/4 combinations, and (4) new image processing techniques to suppress large sidelobe effects due to the solar disk and extended sources. |
Design of a 74-MHz antenna for radio astronomy
| Pengarang | : | W.A. Coles |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 697-704 |
| Abstrak | : | Describes the design and construction of an 8000 m/sup 2/ 74-MHz phased array dedicated to measurement of the solar-wind velocity using the interplanetary scintillation (IPS) technique, and a simple and novel autocalibration system that measures and connects phase and amplitude errors to a level of 1/spl deg/ and 0.2 dB rms. In the IPS technique, intensity fluctuations of compact radio sources caused by plasma turbulence in the solar wind are observed with multiple antennas. The time lag between the antennas is estimated using a cross-correlation analysis. The primary requirement of such a system is sensitivity so that one may observe a large number of compact sources. A secondary requirement is high beam efficiency so that one may observe near the Sun. The scan angle was limited to allow the largest possible array element and thus the simplest feed system. The feed was designed to have independent phase and amplitude control of each element. Although this is not strictly necessary it permits the use of the feed as a phase switched interferometer with which any element can be correlated against any other group of elements. This provides a simple and accurate calibration of the entire array. The antenna was completely prefabricated, the site preparation was minimal, and the installation was quick and accurate. The system is remotely operated. The control information, system diagnostics, and data are transmitted over a leased telephone line. The entire system is powered by storage batteries charged by solar cells. In addition to IFS it has been used extensively for pulsar observations which have similar requirements. |
Design parameters and measured performance of the IRAM 30-m Millimeter Radio Telescope
| Pengarang | : | J.W.M. Baars |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-5, MAY (No. 5) |
| Halaman | : | 687-696 |
| Abstrak | : | The "Millimeter Radio Telescope" (MRT) is operated by the Institute for Radio Astronomy in the millimeter range (IRAM) and is located at 2850-m altitude in the Sierra Nevada, near Granada, Spain. It is a reflector antenna of 30-m diameter with a surface accuracy of 0.08 mm and a pointing accuracy of better than 2 arcsec. The telescope is equipped with sensitive receivers for the atmospheric windows between 0.8- and 7-mm wavelength. The authors describe the optics layout of the receiver and calibration system, which allows simultaneous observations at a number of frequencies. The special design aspects of the antenna, in particular the control of thermal deformations and the achievement of a high reflector and pointing accuracy are described. The authors compare the design computations with the characteristics of the telescope, derived from several years of operation and optimization. The success of the design is demonstrated by observational experience. The authors conclude the paper with a short review of some of the astronomical results obtained with the telescope. |