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antenna.rst 27.86 KiB

Introduction

The Sardinia Radio Telescope is a 64-meter single-dish radio telescope. It is located in the Pranu Sanguni area of San Basilio, Sardinia, Italy, about 40 km north of Cagliari.

Its state-of-the-art technology includes an active surface with 1008 panels, which allows observations at high frequencies (from 0.3 up to 115 GHz). There are three main focal points where reveivers can be placed: primary focus (currently hosting the L-P dual band receiver); Gregorian focus (K-band receiver), and Beam Wave Guide focus (C-band receiver). In total, the telescope can accomodate up to 20 receivers. A number of additional receivers are currently being planned and built.

The telescope can be operated in single-dish or VLBI mode for radio astronomy, geodynamical studies or space science. Its geographical location allows it to observe at declinations above -33 degrees.

A general description of the SRT, including technical commissioning information and first light results, can be found in the technical commissioning paper: Bolli et. al, Journal of Astronomical Instrumentation, Vol. 4, Nos. 3 & 4 (2015) 1550008.

Scientific tests and applications for the SRT are described in the following scientific validation paper: Prandoni et. al, A&A 608, A40 (2017).

Science done with SRT during its early-science run (2016) with the various hardware and software described below can be found here: Science with SRT.

In the following sections, we outline information that is useful for observing with the SRT in the current call for proposals (published September 14, 2018 with a deadline of October 9, 2018). We note that remote observing is not currently available for the Sardinia Radio Telescope; each proposing team will need to send at least one observer to the SRT to prepare the observing schedules and perform the observations on site.

Antenna

The Sardinia Radio Telescope (SRT) is a 64-meter Gregorian radio telescope with shaped optics, a quasi-parabolic main mirror and a quasi-elliptical subreflector.

The antenna's main characheristics are:

Position Pranu Sanguni, San Basilio, Sardinia
Geodetic Coordinates Lat 39° 29' 34.93742" N; Long 9° 14' 42.5764" E (WGS84)
Optical configuration Primary, Gregorian & Beam Waveguide (BWG)
Primary mirror diameter 64 m
Subreflector diameter 8 m
Focal positions primary f/D = 0.33; Gregorian f/D = 2.34; Beam waveguide (BWG) f/D = 1.8
Azimuth range --90 to 450 degrees
Elevation range 5 -- 90 degrees
Slew rate 0.85 degrees/s in azimuth; 0.5 degrees/s in elevation
Frequency coverage 0.3 -- 115 GHz
Primary surface accuracy 300 μm rms
Pointing accuracy (rms) 2 -- 5"

We note that while the elevation limits range from 5 to 90 degrees, observations should be planned for an elevation between 6 and 82 degrees. Only in exceptional cases should the observations go below 6 degrees or above 82 degrees.

Active surface

The primary reflector, which is 64 m across, is made of 1008 aluminium panels (with an RMS ≤ 65 μm each) driven by 1116 electromechanical actuators. This active surface is designed to compensate for the gravitational deformations of the whole surface at different elevations.

The observer can choose among three configurations:

  • shaped in tracking (it adjusts according to the observed elevation position)
  • parabolic in fixed position (optimized for El=45°)
  • parabolic in tracking (it adjusts according to the observed elevation position)

The shaped configuration is used for receivers in the Gregorian and BWG foci, while the parabolic configurations are used for the primary focus systems.

Receivers

In the current call for proposals, the following (cryogenically-cooled) receivers are available in both single-dish and VLBI modes:

RF band (GHz) Type Tsys@90degEL(K) Beamsize (arcmin) Max gain (K/Jy) connected backends
P 0.30-0.36 single-feed 50-80 48 0.52 DBBC,ROACH1
L 1.3-1.8 single-feed 25-35 11.4 0.55 DFB,DBBC,ROACH1,SARDARA
C-high 5.7-7.7 single-feed 32-37 2.7 0.66 TP,DFB,DBBC,ROACH1,SARDARA,XARCOS
K 18-26.5 7-feed 90 0.8 0.66 TP (MB),DFB,DBBC,ROACH1,SARDARA (MB),XARCOS(MB)

(MB) means that the Multi-Beam option is available for observations in K-band with the TP, XARCOS and SARDARA backends.

  • The single-feed, L-P band dual-frequency receiver was installed at the primary focus of the telescope, and therefore requires the parabolic configuration. It allows for simultaneous observations at L and P bands. The polarization type is linear but is also transformed to circular thanks to a hybrid converter.
  • A single-feed C-high band receiver is installed at the Beam Wave Guide (BWG) focus of the telescope. The polarization type is circular.
  • A multi-feed K-band receiver is installed at the (secondary) Gregorian focus. Both C and K band receivers require the shaped configuration. The polarization type is circular.

In the following table, we outline, for each receiver: its frequency coverage; number of feeds; polarization type; focal position; its beam-size in arcmin or arcsec; measurements of the system temperature Tsys at 45 degrees of elevation and antenna gain. Each receiver feed allows for two polarizations.

Band Frequency coverage (GHz) Feeds native polarization type Focal position Beam size Tsys (K) Gain (K/Jy)
P 0.30 -- 0.36 1 linear primary 48'(*) [50-80] 0.52
L 1.3 -- 1.8 1 linear primary 11.4'(*) 25-35 0.55
C-high 5.7 -- 7.7 1 circular beam waveguide 2.7' 32-37(*) 0.66 (*)
K 18 -- 26 7 circular Gregorian 0.8'(**) 90(**) [0.66]

[ ] is an estimate (*) at the band's central frequency (for C-band: 45 degrees EL @ 7.3 GHz) (**) at 22.3 GHz with opacity 0.1 and ground air temperature of 293K.

The FWHM beam size, as a function of the frequency f, can be approximated by the following rule: FWHM(arcmin)=19.7/ f(GHz)