An upgrade of nobeyama radioheliograph to a dual-frequency (17 and 34 GHz) system

The Nobeyama Radioheliograph, originally constructed as a 17 GHz system, was upgraded into a dual-frequency system operating at 17 and 34 GHz on a time sharing basis. For each of the 84 antennas, a frequency-selective sub-reflector, which reflects 17 GHz radio waves into the Cassegrain focus while transmits 34 GHz waves into the primary focus, was installed and a 34 GHz frontend receiver system was mounted in parallel with the existing 17 GHz system. No major modification was introduced to the backend system. Neither were antennas added nor their arrangement changed. With this minimal modification, we have obtained (1) an angular resolution of ∼5″ (at 34 GHz) and (2) a spectral diagnostic capability of cm- to mm-wave emissions from solar flares with temporal resolution up to 100 ms. Daily 8-hour (from ∼22:45 to ∼6:45 UT) operation at dual frequencies started late October, 1995. Final tuning of the new system, such as the calibration and development of image synthesis software tools is still under way. Flare images taken at the dual frequencies are presented and compared with that from the Yohkoh SXT as an example.