A new superconducting filter for S-band observation with VGOS broadband feed at Ishioka VLBI station

Abstract:

VLBI (Very Long Baseline Interferometry) has been playing an important role in maintaining the terrestrial reference frame and monitoring the Earth orientation parameters, which are the part of GGOS (Global Geodetic Observing System) mission. In order to contribute these objectives, Ishioka VLBI station (hereinafter referred to as Ishioka station) of Geospatial Information Authority of Japan has been participating in the IVS (International VLBI Service for Geodesy and Astronomy) sessions since 2015. Since it is a phase of transition to VGOS (VLBI Global Observing System) aimed at 1 mm position accuracy, continuous operation, and providing results with less latency (Petrachenko et al., 2009) and legacy S/X sessions are still main observation which provides geodetic products regularly, Ishioka station participates in both legacy S/X and VGOS broadband sessions. At present, however, it is necessary to change from the broadband feed to the legacy feed in order to join S/X sessions mainly because, with the broadband feed, frequencies below 3 GHz have to be cut in order to avoid saturation caused by the strong RFI (Radio Frequency Interference) in 2-3 GHz. This also means that Ishioka station, with its broadband feed, cannot fully contribute to ‘mixed mode’ session, in which both S/X and VGOS stations participate for combining these observational networks. In order to solve this problem of the RFI so that S band can be received with the broadband feed, we introduced a superconducting filter designed to mitigate the strong RFI.
We confirmed that the new filter (its specification is shown in Figure) can actually suppress the strong RFI in S band. Then, we conducted some test VLBI observations with domestic and international stations and detected fringes. These results show that the new filter works well.
In this presentation, we will report the result of RFI survey around Ishioka station, the filter performance, and the result of test VLBI observations.