Superconductive tapped delay lines for microwave analog signal processing

Passive superconducting tapped delay lines have been fabricated for use as matched filters for multigigahertz bandwidth analog signal processing. Specifically, linear frequency-modulated dispersive delay lines, also known as chirp filters, having a bandwidth of 2.6 GHz centered at 4 GHz and a dispersion time of 35 ns have been constructed. The stripline structure consists of a 4000-Å-thick patterned niobium film sandwiched between 5-cm-diameter, 125-μm-thick sapphire wafers. Two parallel striplines, each 1.6-m long, are wound in a spiral pattern. The taps are backward-wave couplers formed by bringing the two lines into and out of proximity at specified locations. Pulse expansion and compression have been demonstrated with these devices and are in close agreement with a new theoretical model for this class of signal processors.