Roger J. Forse

Hairpin-comb filters for HTS and other narrow-band applications

The folded half-wavelength resonators in hairpin-comb filters all have the same orientation, whereas the orientations of the resonators in conventional hairpin-filters alternates. Hairpin-comb filters are shown to have attractive properties for design of compact, narrow-band filters such as are often desired for high-temperature-superconductivity (HTS) and other applications. The results obtained from two- and four-resonator trial HTS-filter designs are discussed. The filters are seen to have very strong stopbands, and their computed and measured performance are found to be in very good agreement.

Measured performance at 77 K of superconducting microstrip resonators and filters

Results on three types of passive microwave devices fabricated and tested using epitaxial thin films of Tl/sub 2/CaBa/sub 2/Cu/sub 2/O/sub 8/ grown on LaAlO/sub 3/ are reported. A microstrip ring resonator with unloaded Q of 2740 at 77 K and 33 GHz is described. A superconducting 4.6 GHz band-reject filter with unloaded Q greater than 15000 when operated at 77 K is reported. In addition, results on a multiple microstrip bandpass filter are presented. >

Design of HTS, lumped-element, manifold-type microwave multiplexers

Manifold-type frequency multiplexers are especially useful when a sizable number of channels are required. However, they normally use interconnecting transmission lines that could result in an overall structure many wavelengths across. Herein we investigate the design of compact manifold multiplexers using lumped-element filters which are convenient for high temperature superconductor (HTS) realization, while the transmission lines are replaced with lumped-element equivalents. Design examples calculated for frequencies in the vicinity of 0.8 GHz yield element values which are quite feasible for realization in HTS microstrip circuits. The examples indicate that very compact multiplexers should be obtainable.

Thirty-five-GHz downconverter using high-temperature superconductor films

A receiver with an rf band of 34.6 GHz to 35.4 GHz, an integral local oscillator with a frequency of 36.5 GHz, and an IF frequency of 1.1 GHz to 1.9 GHz was designed and fabricated. The rf filter was a three pole distributed design fabricated with High Temperature Superconductor (HTS) films. The IF filter was a 9 pole lumped element design fabricated with HTS films. The local oscillator was a parallel feedback type design using a sapphire resonator shielded by two HTS ground planes. The rest of the elements used normal conductors or semiconductors operated at 77 K. The entire subassembly was integrated into a liquid nitrogen dewar and its performance is reported in the text, with the important figures of merit being low noise figure and low phase noise.

High-temperature superconducting Josephson mixers from deliberate grain boundaries in Tl2CaBa2Cu2O8

Deliberate grain boundaries have been fabricated in epitaxial films of Tl2CaBa2Cu2O8 by growing the films on substrates with localized surface damage and on substrates with surface steps produced with an anisotropic etching process. Bowtie antennas were fabricated to couple millimeter wave radiation into the weak link junctions, which were used as the nonlinear elements. Heterodyne mixing of signals at 55 GHz and 94 GHz was observed in the integrated antenna/detector structures at temperatures below 101 K in the Tl-based films. In addition, observations were made at 55 GHz, using these structures as subharmonic mixers. We have designed an integrated microwave package to measure the noise and conversion efficiency of the grain-boundary junctions at frequencies between 9 GHz and 20 GHz.

Tl-Ca-Ba-Cu-O Thin Film Passive Microwave Devices

We report results on several passive microwave devices fabricated and tested using epitaxial thin films of Tl2CaBa2Cu2O8 grown on LaAlO3. We report microstrip resonators with unloaded Q’s of 15,000 at 80K and 4.83 GHz, and 1440 at 80K and 33 GHz. We report a superconducting 4.6 GHz bandreject filter with unloaded Q greater than 15,000 when operated at 77K.