A Miniaturized High Temperature Superconducting Bandpass Filter Using CPW Quarter-Wavelength Spiral Resonators

A novel compact high temperature superconducting BPF is developed by using coplanar waveguide quarter-wavelength spiral resonators. The filter is a 5-pole Chebyshev BPF with a midband frequency of 5.0GHz and an equal-ripple fractional bandwidth of 3.2%. The CPW spiral resonator is made as small as 1.02times2.1mm
²
. As a result, the 5-pole filter occupies an area of only 7.65x2.11mm
²
, less than one-third that of a newly reported CPW interdigital filter. The filter is fabricated by using 0.5mum YBCO film deposited on an MgO substrate. No bond-wire air-bridges are used and no post-tuning is made in the experiment. The measured filtering characteristics agree well with EM simulations and show low passband insertion losses in spite of the small size of the filter