Microwave coupling of the Josephson junction arrays with an external source

We have fabricated a YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) array of five Josephson junctions designed with additional inductive coupling lines (AICLs). The junctions in this array were dc-biased in parallel to oscillate coherently in-phase and integrated with AICLs to improve the impedance matching between this array and external circuits such as a waveguide. The effect of AICLs was investigated by studying its influence on the current-voltage characteristics of the Josephson junction array (JJA) under external microwave irradiations with frequency of 22 GHz. The experimental results show that the behavior of the Shapiro-steps depends upon the effective inductance of AICLs which affects the total impedance and microwave coupling. We were able to obtain an oscillation frequency of about 73% of the maximum available frequency calculated from the characteristic voltage of the Josephson junctions in the array at a temperature of 12 K. By calculating the total impedance of the array, we obtained the suitable parameters of the array for microwave coupling with waveguide for various values of inductance, ac frequencies and number of Josephson junctions.