Daniel C. Buck

Low- and high-temperature superconducting microwave filters

Stripline and microstrip filters at X-band were designed and fabricated using low- and high-temperature superconductors in quarter-wave, parallel-coupled section configurations. Low-temperature superconducting niobium thin films, deposited on single-crystal sapphire, were used to build to six-pole stripline filters with adjacent passbands and approximately 3 dB crossovers and 1.2% bandwidth. Four- and six-pole microstrip filters were made with in situ epitaxial YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films on LaAlO/sub 3/ substrates. All the YBCO filters showed 77 K passbands with clean skirts and high out-of-band rejection. The six-pole filters had adjacent passbands with -28 dB crossovers and 1.5% bandwidth. >

High temperature superconducting space-qualified multiplexers and delay lines

A high temperature superconducting (HTS) four-channel multiplexer and a delay line were fabricated, space qualified and tested as part of the U.S. Navys High Temperature Superconductivity Space Experiment II (HTSSE-II). The multiplexer had an architecture that included two branch-line hybrids and two identical parallel-coupled line filters per channel. Its operation was centered at 4 GHz, with 50-MHz-wide channels. It was fully integrated, with microstrip interconnections between channels and thin-film load terminations in the out-of-phase port of the output hybrid. The delay line was made up of two cascaded modules for a total delay of 45 ns between 2 and 6 GHz. Both devices were made using 5-cm-diameter LaAlO/sub 3/ wafers coated with epitaxial thin film YBa/sub 2/ Cu/sub 3/O/sub 7/, on both sides in the case of the delay line. Both devices operated at 77 K.

High-temperature superconducting wide band delay lines

Stripline non-dispersive delay lines with 20 GHz of bandwidth were designed and fabricated using YBCO thin films deposited on both sides of 2-inch-diameter, 10-mil thick LaAlO/sub 3/ wafers. A double-wound spiral configuration was used yielding a line length of approximately 150 cm. Novel approaches were used to minimize the effect of air gaps between the two substrates needed to form the stripline structure, and to realize a wide band transition from the coaxial external connections to stripline. Experimental results showed 5 dB of insertion loss at 20 GHz, with 1 dB amplitude ripple over most of the 0-20 GHz, range for a 22.5 ns delay.<<ETX>>

High-temperature superconducting four-channel filterbanks

A high-temperature superconducting four-channel filterbank was fabricated and tested. The device was made in microstrip configuration with an architecture that included two branch-line hybrids and two identical parallel-coupled line filters per channel. The filterbank was fully integrated, with microstrip interconnections between channels and thin-film load terminations in the out-of-phase port of the output hybrid.<<ETX>>