Image: PHAROS2 cryogenic array of Vivaldi antennas and dome-like vacuum window.

We describe the development of PHAROS2, a cryogenic Phased Array Feed (PAF) with digital beamformer for radioastronomy application across 4-8 GHz (C-band). The instrument is a technology demonstrator developed in collaboration with international partners in the framework of the PAF Advanced Instrumentation Programme for the Square Kilometer Array (SKA). It was designed to operate at the primary focus of a large radio telescope.
After an introduction to the phased array feed technology, we will present PHAROS2. The instrument is based on an array of 10×11 dual-polarization Vivaldi antennas cryogenically cooled at 20 K along with low noise amplification modules (LNAs) located inside a cryostat. A multi-channel “warm section” receiver allows
processing the signals from a subset of 24 antenna elements of the Vivaldi array by downconverting them to an intermediate frequency (IF) range, 375-650 MHz, suitable for digitization by a digital beamformer. The beamformer can synthesize four independent beams across the 275 MHz instantaneous IF bandwidth in its FPGAs (Field Programmable Gate Arrays).
Most of the PHAROS2 hardware and firmware were developed at INAF. Some of the PHAROS2 subsystems were tested in the INAF-OA Cagliari laboratories before they were shipped to the Jodrell Bank Observatory (JBO), UK, where the PAF was fully integrated and tested on the ground.
PHAROS2 was mounted on the e-Merlin 25-m diameter Pickmere antenna at JBO for astronomy validation during three weeks in the period Oct. 23-Nov 4 th , 2019. This was the first-ever cryogenic Cband PAF installed on a radio astronomy antenna. We report on the preliminary ground test results and antenna test results
that have been obtained over the past few months.
Furthermore, we will describe the prospects for the continuation of the PHAROS2 project and for the development of new PAF technologies within INAF, which might find application on a future high-performance cryogenic C-band PAF for the SRT. Some of these technologies might also be used to build a room-temperature
demonstrator for space debris application.