Sensitivity and Antenna Noise Temperature Analysis of the Feed System for the Onsala Twin Telescopes

Other conference contribution, 2017

The demand for higher precision measurements in Very Long Baseline Interferometry (VLBI) continues to grow, which drives the technical development of next generation international VLBI stations called the VLBI Global Observing System (VGOS). The VGOS design includes the idea of twin telescopes, i.e. two identical telescopes that will be used for continuous observations to study geodynamical processes. Such a twin telescope system has recently been installed at the Onsala Space Observatory, Sweden. The Onsala twin telescopes (OTT) are 13.2 m diameter, dual-reflector systems with a ring-focus sub-reflector. In this paper we present the estimated performance, focusing on the achievable system equivalent flux density (SEFD), sky noise modeling, and antenna noise temperature. We evaluate the system for two different cryogenic wideband quad-ridge flared horn (QRFH) feed setups operating over 3-18 GHz and 4.6-24 GHz. Analysis based on measured feed data shows a low antenna noise temperature and that SEFD of 1000 Jy can be achieved for the system. The result from Y-factor test shows TREC = 10 K over most of the frequency band.