FORTY FIVE NANOSECONDS SUPERCONDUCTING DELAY LINES

We report on the design, simulation, fabrication, and measurement of very long superconducting coplanar waveguide delay lines on 3-inch diameter LaAlO3 substrates. Variations of the design involving the addition of a ground plane on the backside of the substrate and/or the use of gold wire-bond bridges to electrically connect the in-plane ground planes are investigated. A delay of 45 nanoseconds is measured for a line length of 4.3 meters. The best response is obtained with wire-bond connections and no backside ground plane. A resonance-free insertion loss of less than 0.01 dB/ns is obtained with a 1.7 GHz bandwidth for NbN at 4.2 K. This is to be compared with a loss of 0.1 dB/ns for a 50 nanoseconds 0.141 - inch O.D. copper coaxial delay line which weighs 1.5 lbs, and 0.02 dB/ns for a 60 nanoseconds 1 - inch O. D. copper coaxial delay line which weighs 45 lbs. Experiments are underway to fabricate and measure a similar YBCO line.