L. V. Filippenko

Design and experimental study of superconducting left-handed transmission lines with tunable dispersion and improved impedance match

  1. E. A. Ovchinnikova,
  2. S. Butz,
  3. P. Jung,
  4. V. P. Koshelets,
  5. L. V. Filippenko,
  6. A.S. Averkin,
  7. S. V. Shitov,
  8. and A. V. Ustinov
We continue detailed study of microwave properties of a superconducting left-handed tunable CPW transmission line (LHTL). The line consists of a central conductor, loaded with series
of Josephson junctions as fixed inductors; the line is shunted with SQUIDs as tunable inductors. The inductance of the SQUIDs is varied in the range of 0.08-0.5 nH by applying an external dc magnetic field. The circuit is designed to have left- and right-handed transmission bands separated by a variable rejection band. At zero magnetic field, we observed only one pass-band between 8 and 10 GHz within the frequency range of 8-12 GHz. The rejection band is anticipated to appear between 10 GHz and 11 GHz by design, and it has been detected in our previous work. To solve the problem of standing waves and RF leak in measurements of our experimental 20-cell LHTL, we have designed a high-ratio (5-50 Ohm) wideband (8-11 GHz) impedance transformer integrated at the chip, along with improved sample holder. The experimental data are compared with numerical simulations.
arxiv pdf

Ultra-compact tunable split-ring resonators

  1. A. Vidiborskiy,
  2. V. P. Koshelets,
  3. L. V. Filippenko,
  4. S. V. Shitov,
  5. and A. V. Ustinov
We propose tunable superconducting split-ring resonators (SRRs) employing nonlinear Josephson inductance. A fraction of SRR is replaced by Nb-AlOx-Nb Josephson tunnel junctions connected
in parallel and forming a superconducting quantum interference device (SQUID), whose inductance is sensitive to the external dc magnetic field. Due to the lumped nature of the Josephson inductance, the SRR can be made very compact and its resonance frequency can be tuned by applying magnetic field. We present the model, results of extensive EM-simulation and experimental data for the SRR weakly coupled to a transmission line within frequency range 11-13 GHz.
arxiv pdf