High temperature superconducting Y-Ba-Cu-O films were prepared on MgO polycrystal substrates by the sol-gel process. The average transition temperature and the surface resistance are 83K and 2.8mQ (at 30 K and 9.9GHz, input power = -lOdBm), respectively. We fabricated a YBCO coplanar waveguide (CPW) quarter-wavelength (A/4) resonator around 2GHz (the length of the resonator is one half as long as that of the popular half-wavelength (A/2) resonator) and compared its RF properties with that of a A/2 resonator. Moreover, 2-pole CPW bandpass filter using YBCO sol-gel film was constructed with capacitively coupled A/4 resonators. It has a narrow fractional bandwidth (3.60%) at 30K.
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