International audienceThe current status of the large decameter radio telescope UTR-2 (Ukrainian T-shaped Radio telescope) together with its VLBI system called URAN is described in detail. By modernization of these instruments through implementation of novel versatile analog and digital devices as well as new observation techniques, the observational capabilities of UTR-2 have been substantially enhanced. The total effective area of UTR-2 and URAN arrays reaches 200 000 m2, with 24 MHz observational bandwidth (within the 8–32 MHz frequency range), spectral and temporal resolutions down to 4 kHz and 0.5 msec in dynamic spectrum mode or virtually unlimited in waveform mode. Depending on the spectral and temporal resolutions and confusion effects, the sensitivity of UTR-2 varies from a few Jy to a few mJy, and the angular resolution ranges from ~ 30 arcminutes (with a single antenna array) to a few arcseconds (in VLBI mode). In the framework of national and international research projects conducted in recent years, many new results on Solar system objects, the Galaxy and Metagalaxy have been obtained. In order to extend the observation frequency range to 8–80 MHz and enlarge the dimensions of the UTR-2 array, a new instrument – GURT (Giant Ukrainian Radio Telescope) – is now under construction. The radio telescope systems described herein can be used in synergy with other existing low-frequency arrays such as LOFAR, LWA, NenuFAR, as well as provide ground-based support for space-based instruments
It has recently been suggested that the absorption line v = 26.13 MHz that we had detected in the direction of Cassiopeia A might be a recombination line due either to carbon (C631α) present in H I clouds or to heavier elements of hot gas. Observations reported here taken in February 1981 suggest that the low-frequency attenuation in the spectrum of Cas A is due to the presence of a cold cloud of ionized carbon.
The possibility of forming a set of spatially dispersed and mutually orthogonal beams in an array antenna has been known long ago. The method for obtaining a device that forms a fan of beams for arrays with the number of elements and beams equal to was suggested by Butler. Realizing a fan of mutually orthogonal beams for arrays with any , was shown by us in "Synthesis of pattern forming networks" Radio Engineering and Electronic Physics, vol. 27, no. 7, pp. 28-35, 1982. The schemes of the corresponding devices for , 6 and 8 were also represented, however, the method for building a concrete scheme was described there without details. The present paper is dedicated to the procedure of synthesizing a beam-forming device based on the factorization of its transmission matrix, at this point, each factor represents a matched and decoupling hybrid. As a result, the beam-forming network is represented by a cascade connection of elementary matrices containing one hybrid or several 90 phase shifters. The procedure is illustrated using examples of synthesizing matrices for and having broadside beams, and also that for where the left and right beams are symmetrical as normally assumed for "Butler" matrices. Furthermore, the scheme with is compared with the corresponding "Butler" matrix.
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