Cross-Coupled Narrow-Band YBCO Filters with Spurious Suppression by Using a Tap-Connection Technique

다국어 초록 (Multilingual Abstract)

Narrow-band microstrip cross-coupled band-pass filters based on a quadruplet geometry were
designed for wireless-communication applications. High-Tc superconducting (HTS) filters were fabricated
by patterning YBa2Cu3Oy (YBCO) films double-side deposited on 20-mm-square and 0.5-
mm-thick LaAlO3 substrates. The filters with skew-symmetric feed were designed with a center
frequency at 1.9 GHz and a bandwidth of 20 MHz. The inductive coupling between the non-adjacent
resonators produced a pair of transmission zeros in the frequency response. Also observed was an
additional pair of transmission zeros that enhance the out-of-band rejection characteristics. The
realized YBCO filter showed a center frequency at 1.925 GHz with a bandwidth of 20 MHz and a
minimum insertion loss of about 0.74 dB. Furthermore, a tap-connection technique was applied to
cross-coupled HTS band-pass filters so as to suppress the second and/or the third passbands, which
were spurious and undesirable. To improve the out-of-band performance of the band-pass filters,
we tapped the input/output microstrip lines at certain locations. In this research, we confirmed
that by tapping somewhere along the input/output microstrip lines, a /4 open stub or a /2 short
stub, where refers to the guided wavelength at 2fo or 3fo, may effectively suppress harmonics at
2fo and/or 3fo by more than 25 dB. The simulated and the experimental results are discussed.

참고문헌 (Reference)

1 Jia-Shen G. Hong, "Microstrip Filtersfor RF/Microwave Applications, edited by Kai Chang" Wiley 2001