Fixed-frequency and frequency-agile (Au,HTS) microstrip bandstop filters for L-band applications

In this work, we report on the performance of a highly selective, compact 1.83×2.08 cm² (~0.72×0.82 in.²) microstrip line bandstop filter of YBa₂Cu ₃O_7-δ (YBCO) on LaAlO₃ (LAO) substrate. The filter is designed for a center frequency of 1.623 GHz for a bandwidth at 3 dB from reference baseline of less than 5.15 MHz, and a bandstop rejection of 30 dB or better. The design and optimization of the filter was performed using Zeland´s IE3D circuit simulator. The optimized design was used to fabricate gold (Au) and High-Temperature Superconductor (HTS) versions of the filter. We have also studied an electronically tunable version of the same filter. Tunability of the bandstop characteristics is achieved by the integration of a thin film conductor (Au or HTS) and the non-linear dielectric ferroelectric SrTiO ₃ in a conductor/ferroelectric/dielectric modified microstrip configuration. The performance of these filters and comparison with the simulated data will be presented