Development of a Radio Interferometer Operating at 12GHz for Education and Research

Abstract

We developed a radio interferometer system operating at 12GHz for educations and possibly for research. The commercial components are usually used for satisfying a low cost strategy, and the driving system is made to resist the strong wind, because the installation site is located near the seaside. The interferometer system consists of three off-axis parabola antenna, whose diameter is 1.8 m. The baselines between antennas are about 4, 19, and 20 m, so about 4 resolution can be acquired. The baseline vectors are accurately measured by using a theodolite, a light wave distance measurement, and GPS (Global Positioning System). The center frequency of the receivers is 12.177 GHz, and the bandwidth is 6 MHz. The receiver is able to observe the methanol line (12.178 GHz) and continuum from the Sun, the Moon, and the Galactic plane. The signals of each receiver are sampled and quantized by the digitizer, and then software correlation is conducted with the developed parallel process program. We succeeded in finding fringes toward the Sun, Moon, Crab Nebula, Cassiopeia A. By using a Nobeyama solar radio image taken at 17 GHz with a bright spot at the center of solar disk, we tried to calibrate uncertainties involving signal cable length, but it was found to be only partially successful. In order to make images of celestial objects, more careful treatment seems necessary with the use of phase calibrator or with a method similar to self-calibration without the phase calibrator.