Hideki Ujihara

First Fringe Detection with VERA's Dual-Beam System and Its Phase-Referencing Capability

We present the results of the first dual-beam observations with VERA (VLBI Exploration of Radio Astrometry). The observations of a pair of H2O maser sources, W 49N and OH 43.8−0.1, were carried out on 2002 May 29 and July 23, and fringes of the H2O maser lines at 22GHz were successfully detected. While the residual fringe phases of both sources showed rapid variations over 360 ◦ due to the atmospheric fluctuation, the differential phase between the two sources remained constant for 1 hour with an r.m.s. of 8 ◦ , demonstrating that the atmospheric phase fluctuation was effectively removed by dual-beam phase referencing. An analysis based on the Allan standard deviation reveals that the differential phase is mostly dominated by white phase noise, and the coherence function calculated from the differential phase shows that after phase referencing the fringe visibility can be integrated for an arbitrarily long time. These results demonstrate VERA’s high capability of phase referencing, indicating that it is a promising tool for phase-referencing VLBI astrometry at 10 µas-level accuracy.

Development of wideband VLBI system with transportable small telescope for distant frequency transfer

Very long baseline interferometry (VLBI) is one of the technologies to enable comparisons of atomic frequency standards at intercontinental baseline. Our group is working on development of wideband VLBI system with transportable small diameter antennas for VLBI application to the frequency transfer. The system is composed of pair of small diameter antennas and large diameter antenna, which observes ultra-wide frequency range at 3-14GHz. This paper reports the overview of the project and current status of the development.

Delopement of mutimode horns and wideband feed for radio telescopes

Multimode horns were developed for 8.4GHz, 22GHz, 43GHz receiver systems of ASTRO-G/VSOP-2 satellite for Space-VLBI, and for 6.7GHz of VERA 20m radio telescopes of National Astronomical Observatory in JAPAN and 25m Shanghai Radio telescope in China. Rational bandwidth of these horns in low cross polar level are 20-30%, and their thin walls without corrugation and shortened length are the best for the satellite use. Also, wideband feeds will be presented, which are now developing for SKA and VLBI2010, which is a kind of Tapered Slot Antenna or other of traveling wave antenna.

Development of QZSS-mobile station

As we designed and constructed the QZSS mobile station, we transported it to Okinawa Electromagnetic Technology Center and Kashima Space Technology Center. At each place we carried out time comparison experiments. This paper describes some results of the time comparison experiments.