We present the radio properties of optically selected quasars with z>=3. The complete sample consists of 102 quasars with a flux density level S_1.4_>=100mJy in a declination range -35{deg}<=Dec.<=+49{deg}. The observations were obtained in 2017-2020 using the radio telescope RATAN-600. We measured flux densities at six frequencies 1.2, 2.3, 4.7, 8.2, 11.2, and 22GHz quasi-simultaneously with uncertainties of 9-31 per cent. The detection rate is 100, 89, and 46 per cent at 4.7, 11.2, and 22GHz, respectively. We have analysed the averaged radio spectra of the quasars based on the RATAN and literature data. We classify 46 per cent of radio spectra as peaked-spectrum, 24 per cent as flat, and none as ultra-steep spectra ({alpha}2.5. We have not found any significant correlation between z and {alpha}. Several new megahertz- peaked spectrum (MPS) and gigahertz- peaked spectrum (GPS) candidates are suggested. Further studies of their variability and additional low-frequency observations are needed to classify them precisely.
Cone search capability for table J/MNRAS/508/2798/table1 (Parameters of 102 objects)
