Suppression of spurious harmonic responses in superconducting microstrip spiral filters using gold overlay and stagger tuning

Frederick Huang, Pietro Bolli, Sergio Mariotti
2020 IET Microwaves, Antennas & Propagation  
The higher order resonances of microwave superconducting filters with spiral resonators were suppressed, giving a very wide stop-band. In one filter spirals were modified to have equal fundamental resonances, but different higher order resonances, by adding stubs and using non-uniform line width. The higher resonances were reduced to −39 dB, in a stop band up to 4.3 times the pass band centre. In another filter, parasitic resistive resonators were added, suppressing the responses to −57 dB. The
more » ... resistance is provided by patterning the 200 nm gold overlay already required for the external contacts. The increase in pass band loss is not measurable. Measurements of a single spiral resonator with a gold-YBCO bi-layer (200 and 600 nm respectively) suggest that the resistivity of the gold layer at 15 K is the order of 22 times that of bulk gold, a slight advantage for the present application. At 100 K, it is about double. Fig. 6 Layout of filter 3 (Filters 1 and 2 have slightly different dimensions; also filter 1 has no gold/YBCO resonators while filter 2 has only the gold/YBCO resonators outside the main resonators). Overall length is 25.84 mm, less than a half wavelength for this substrate 2128
doi:10.1049/iet-map.2019.1113 fatcat:h3rcpsx7qbervb7aw3x4ifkc4e