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Superconducting RF Filters for Advanced Signal Processing


High-performance filters can be enabled by operation at cryogenic temperatures. The lower loss associated with superconductors can enable unique functionality, such as power-limiting behavior and extremely high selectivity. These two unique characteristics can be combined to develop, for example, auto-limiting mulitplexers, which can be used to excise large in-band interference signals without attenuating smaller signals of interest within a given frequency band. The further development of superconducting filters is of interest for both analog signal processing applications such as multiplexers, as well as for control of signals generated by precision microwave sources. Auto-limiting circuitry based on superconducting devices has been under development at NIST for a number of years, and commercialization of the technology has the potential to improve the performance of sensitive RF and microwave receivers. The results of this research can also be applied for high-performance filtering necessary in the development of precision microwave sources based on superconductor technology.

Subtopic goals include the development of compact superconductor filters for application in auto-limiting multiplexers and precision sources based on superconductor technologies. For signal-limiting applications, there is particular interest in frequency bands centered around 1 GHz and 3.5 GHz. The filters are expected to be implemented in microstrip technology on microwave-friendly substrates such as sapphire, and packaged for operation on closed-cycle cryocooler-based platforms.

Phase I expected results:
Designs and simulated results for compact microstrip filters based on superconductor technology for approximately 20 MHz (3 dB) bandwidth operating at 3.5 GHz. Successful designs should emphasize compact filter layouts, and be designed for high temperature superconductors deposited on high-quality sapphire substrates. Results of simulations are required in order to evaluate impact of phase II work for fabrication and packaging of the most promising designs.

Phase II expected results:
Phase II expected results include fabricated superconductor filters for operation at 3.5 GHz with approximately 20 MHz (3dB) bandwidth. Up to two packaged devices for operation at cryogenic temperatures on a compact closed-cycle cryocooler as well as one or more unpackaged die are required for detailed evaluation of performance in both linear and nonlinear regimes.

Collaboration may be available in terms of discussion of design configurations, as well as simulated response; preliminary measurements of unpackaged devices that are amenable to wafer-probe style measurements; and support for advanced device modeling.

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