THE NOBEYAMA RADIOHELIOGRAPH

A new 17-GHz radio interferometer dedicated for solar observations was constructed in 2 years at Nobeyama, Nagano. It consists of eighty-fou r 80-cm-diameter antennas arranged in a Tee-shaped array extending 490 m in east-west and 220 m in north-south directions. Since late June o f 1992, radio full-disk images of the Sun have been observed for 8 h e very day. The spatial resolution is 10'' and the temporal resolution i s 1 s and also 50 ms for selected events. Every 10 s, correlator data are synthesized into images in real time and displayed on a monitor sc reen. The array configuration is optimized to observe the whole Sun wi th high spatial and temporal resolution and a high dynamic range of im ages. Image quality of better than 20 dB is realized by incorporation of technical advances in hardware and software, such as 1) low-loss ph ase-stable optical-fiber cables for local reference signal and IF sign als, 2) newly developed phase-stable local oscillators, 3) custom CMOS gate-array LSI's of 1-b quadra-phase correlators for 4 x 4 combinatio ns, and 4) new image processing techniques to suppress large sidelobe effects due to the solar disk and extended sources.