Superconductive delay-line technology and applications

Microwave analog signal-processing filters have been realized in the form of coupled niobium striplines on silicon dielectric substrates. Device responses with ± 2-dB amplitude accuracy and 9°-rms phase error have been achieved in amplitude-weighted filters with 37.5 ns of dispersion and 2.3-GHz bandwidths. Relative side-lobe levels of -26 dB and less are currently obtained. The achievable dispersion for stripline circuits on a single pair of 5-cm-diameter, 125-μm-thick wafers is limited to about 40 ns by the electro-magnetic coupling between neighboring lines. To achieve greater dispersion two approaches are under development: (1) Stripline circuits are being fabricated on multiple wafer pairs which are physically stacked and electrically concatenated to produce dispersive delay lines with 4-GHz bandwidth and 75-ns dispersion time. Phenolic resin is used as an adhesive to ensure the mechanical integrity of the stacked structure. (2) A technique to fabricate dense stripline circuits on very thin (15-μm) single-crystal silicon superstrates supported by thicker substrates has been demonstrated and preliminary results will be described. A chirp-transform system capable of real-time spectral analysis has been constructed using a pair of the superconductive delay-line filters. A resolution of 43 MHz over an unprecedented 2400-MHz bandwidth with amplitude uniformity of ±1 dB and side-lobe levels of -18 dB was demonstrated.