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The goal of the project was to cope with three problems concerning the application of superconductors to microwave industrial problems:
1) to define really pertinent devices. Operational devices must be defined from specific needs and require a careful analysis of the whole problem (expected performance, volume, weight, including cryogeny).
2) to produce homogeneous reproducible films. Most of the published results correspond to small samples (typically 10 x 10 mm) 50 x 50 mm areas are highly desirable for practical applications.
3) to make these devices. Operational devices imply very tight specifications defined by end-users, which adds design difficulties independently of the superconducting aspect. They require top level modelling. The initial specifications were:
1- YBCO thin films: 500 nm thick,
2- surface resistance Rs< 0.5 milliohm at 10 GHz and 77 K,
3- homogeneous area: Ø 50 mm
4- ultimate objective: Rs = 0.1 milliohm
5- multiple tap delay line: more than 16 taps with 0.1 to 1 ns delay between taps
6- narrow band filter: relative bandwidth < 0.5 %
7- 3D high Q resonators: Q > 300 000 updated to 1 000 000 at 10 GHz
8- slow wave effect demonstrator: slowing factor > 5
9- microwave superconducting detectors competitive with semiconducting diodes.

Most of these specifications (1,2,3,5,6,7) have been met except the more exploratory ones (4,8,9). The material specifications (1,2,3,4) provide a two orders of magnitude improvement versus the values of the metallization used in microwave devices at room temperature. This implies to reconsider the design of some usual components: planar resonators can replace metallic cavities with equivalent performances for the design of filter banks and with a considerable gain in weight and volume especially at frequencies below 5GHz. At the completion of the research (01/03/1996), several objects are available:
low Rs superconducting films: Rs < 0.4 milliohm;
C band narrow bandwidth filter: bandwidth = 0.5 to 1 %;
high Q 3D resonators (10 GHz): Q = 1 300 000;
tapped delay line (up to 10 GHz): delay = 4 nanoseconds.
The industrial objectives of this project are:

- to demonstrate the real avaibility on the european market of microwave quality HTSC thin films i.e.: surface resistance lower than 0.5 milliohm at 10 GHz and 77k.

- to supply of strategic microwave components using these films.

The choice of components concerns:

- multiple tap delay line : basic component for analog signal processing: goniometer, spectrum analyser, correlatof for spread spectrum communications,

- filter bank,

- high Q resonator (Q>1000000) for low noise oscillators.

The main general interest concerns the improvement of both spatial and ground communications, and to safer air traffic control. These strategic areas are in the business of the proposers.

In order to realize this objective, the project plans to control the main technics used for superconducting material process.

- sputtering film deposition
- wet etching for patterning
- microwave circuit modelling
- specific packaging (microwave and cryogeny)
- microwave testing.

Call for proposal

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Domaine de Corbeville
91404 Orsay

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