Medicina Radio Observatory

Astronomical observatory near Bologna, Italy

The Medicina Radio Observatory is an astronomical observatory located 30 km from Bologna, Italy. It is operated by the Institute for Radio Astronomy of the National Institute for Astrophysics (INAF) of the government of Italy. The site includes:
32 metre diameter parabolic antenna for observing between 1.4 and 23 GHz. The 32 m antenna is used as a single dish instrument for astrophysical observations (such as water and methanol maser spectroscopy), SETI experiments and radar monitoring of Near Earth Objects. In interferometric mode it functions as a VLBI station, part of the European VLBI Network (EVN). 564 by 640 m (30000 square meter) multi element Northern Cross cylindrical parabolic transit radio telescope for observing at 408 MHz.

The Northern Cross Radio Telescope (also known as the Medicina Northern Cross (MNC)) (and Croce del Nord in Italian) is one of the largest transit radio telescopes in the world. Observations are focused around 408 MHz (UHF band), corresponding to 73.5 cm wavelength. The older receivers of the telescope function with a 2.5 MHz wide frequency band, while the upgraded parts have a 16 MHz bandwidth. The telescope is steerable only in declination, meaning that it can solely observe objects that are culminating on the local celestial meridian.

The Cross is currently used as a pathfinder for the Square Kilometre Array. The work is focused on studying the amplification and filtering of signals between the LNA (Low Noise Amplifier) output and the analog to digital converter input for the SKA. The Medicina Radio Observatory is studying all problems related to "antenna array implementation" through a prototype installation called MAD (Medicina Array Demonstrator). The observatory staff have also built new receiver demonstrators for the SKA called BEST (Basic Element for SKA Training), part of the EU funded SKADS (SKA Design Studies) programme. The project started in 2005 and finished in 2009. It involved the installation of the new receivers on some reflectors of the north–south section (and later east–west section) of the Northern Cross telescope, along with new analog fiber optic and coaxial digital finks from the front end receiver boxes to the back ends. The BEST project was divided in three parts:
BEST 2 – 32 receivers were installed on 8 reflectors of the north–south arm. BEST 3lo focused on lower frequencies – between 120 and 240 MHz. Log periodic antennas optimized for 120–240 MHz, along with 18 receivers were installed on part of the east–west arm.

There is an ongoing effort to use the 32 meter dish as a receiver for radar based tracking of artificial satellites and space debris in Earth orbit. The system functions as a bistatic radar, where an emitter located in a different location sends a signal, which bounces off objects in orbit and the echo is picked up by a receiver. The 32 meter dish acts as a receiver, while usually the Yevpatoria 70 meter located in Crimea, functions as a transmitter. The systems can either actively track debris to determine their orbit more precisely or utilize a technique called beam park, where the transmitting and receiving antennas are kept fixed at a given position and the debris pass in and out of the observed area. The measurements obtain through such a system can be used to determine object radar cross section, time of peak occurrence, polarization ratio, bistatic doppler shift and target rotation. In one of the carried out tests, Yevpatoria Medicina system was able to detect an object with an estimated radar cross section of 0.0002 square meters, which was created by the Iridium 33 and Kosmos 2251 satellite collision. The system can also function as a multistatic radar using the 32 meter receivers at Medicina, the Noto Radio Observatory in Italy and the Ventspils Starptautiskais Radioastronomijas Centrs in Latvia. The Northern Cross radio telescope has also been part of space debris tracking studies, utilized as a multiple beam receiver for a bistatic radar system. The first tested configuration is a quasi monostatic radar system with a 3 m dish as the transmitter, located in Bagnara – 20 km from the receiver. The second configuration was a simulation of a true bistatic radar system with 7 m dish as the transmitter located at the site of the Sardinia Radio Telescope (SRT). The system has a maximum field of view of about 100 square degrees and a collecting area of approximately 27400 square meters and is capable of providing up to 22880 beams, each 4 by 4 arcminutes wide. Tracking the sequence of beams that are illuminated, makes it possible for the system to track with a higher level of detail, with respect to the single beam systems, the ground track of a transiting object.