Effects of magnetic fields and microwave radiation on I-V characteristics of YBa2Cu3Oy high-T, Josephson junctions, SQUIDS and Josephson arrays were reported in this experiment, with special emphasis focused on the effects of microwave radiation. In addition to the ordinary constant-voltage steps resulting from the ac Josephson effect, noninteger constant voltage steps are occasionally observed under microwave radiation. We attribute these noninteger constant-voltage steps to the flux coupled to junctions or SQUIDS. Resistive SQUIDS disclose V-Φmodulation without a biased current. The peak to peak value AV of a V-Φ curve is enhanced by microwave radiation.