HYSTERESIS EFFECT IN MICROWAVE-POWER TRANSMISSION OF HIGH-TEMPERATURESUPERCONDUCTING COPLANAR TRANSMISSION-LINES

We have an unusual hysteresis loop in rf power dependence of high-temp erature superconductor (HTS) coplanar transmission lines. At 77 K and 1 GHz, the signal transmission was Linear (insertion loss <0.1 dB) unt il the input power (P-in) reached a critical value of P-c=0.4 W. An ab rupt drop by similar to 37 dB in the transmitted power (P-out) was obs erved at P-in=P-c followed by a slow increase (P(out)proportional to P -in(0.62)) for P-in> P-c. As P-m was then decreased, it retraced the p revious curve only until P-in=P-c. However, as P-in was reduced furthe r P-out did not rise until P-in=158 mW, at which P-out started to incr ease rapidly and returned to the linear regime for P-in<71 mW. Such a sharp transition and a strong hysteresis effect were unique to the HTS line whereas a gold line with an identical structure did not exhibit these characteristics. This behavior may be utilized for potential app lications of new HTS microwave power (current) limiters and switches. Several possible origins for the hysteresis effect are proposed and di scussed. (C) 1995 American Institute of Physics.