Intermodulation distortion measurements of a microstrip band-pass filter made from double-sided YBa2Cu3Ox, films

A microstrip three-pole band-pass filter, with a midband frequency of 9.5 GHz and a fractional bandwidth of 2%, has been fabricated using double-sided YBa2Cu3Ox (YBCO) films on MgO substrates. The nonlinear behavior of this filter was studied by intermodulation distortion measurements. The insertion loss at the midband frequency was less than 0.1 dB and the return loss was better than 15 dB throughout the passband at 55 K. This filter showed relatively high power handling capabilities, with third-order intercept larger than +60 dBm at 55 K. The third-order intermodulation distortion products of this filter were found to vary with frequency in the passband, being larger near each of the band edges than at the midband. These increases in the nonlinearity near the band edges are attributed to the increase in the average stored energy in the filter, which is confirmed by the increase in the group delay near the band edge. (C) 1995 American Institute of Physics.