- Email: [email protected]
Superconductors and cryotechnology for space communications
Physica C 372–376 (2002) 489–492 www.elsevier.com/locate/physc
Superconductors and cryotechnology for space communications Tobias K€ asser a,*, Michael Viertel a, Ralf B€ olter a, Christian Neumann b, F. Schnell b a
b
Bosch SatCom GmbH, UC-RA/EMD, D-71501 Backnang, Germany Robert Bosch GmbH, Corporate Research and Development, D-70049 Stuttgart, Germany
Abstract In commercial satellite applications, superconductive devices offer the advantage of a reduction in mass and volume, combined with improved high-frequency performance. The Bosch space experiment clearly demonstrates these benefits, and it also shows the applicability of the technology with respect to space qualification procedure. Furthermore, this article describes improved design methods for planar superconducting filters, combining high Q-values with complex designs. 2002 Elsevier Science B.V. All rights reserved. Keywords: Cryogenics; Satellite communications; Filter design
1. Introduction One major application of high-temperature superconductivity is passive communication technology. The benefit of superconductivity and cryotechnology in space communications lies in the miniaturisation of communication systems as well as in improved performance with respect to e.g. selectivity or noise figure. In this contribution we will report on the status of the Bosch HTSC Space Experiment. The engineering-qualifying model clearly demonstrates the above mentioned advantages, and it is fully space-
*
Corresponding author. Tel.: +49-7191-930-1217; fax: +497191-930-1850. E-mail address: [email protected] (T. K€asser).
qualified with respect to typical commercial requirements. Furthermore, we will focus on our ongoing work which aims at a higher efficiency of cryogenic satellite payloads and at improved RF performance. We deal with problems arising when designing high-order filters combining complex designs and low electrical losses simultaneously.
2. Bosch space experiment It is the aim of the experiment to demonstrate the benefits of superconducting devices under real operating conditions. Furthermore, it is the aim to demonstrate the full applicability and qualificability of the materials involved, of all related assembly and integration techniques and of the
0921-4534/02/$ - see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 0 7 2 9 - 3
490
T. K€asser et al. / Physica C 372–376 (2002) 489–492
surrounding cryosystem. In space business, costumers are conservative, and a space experiment is a keystone in introducing a new technology into market. Other space experiments with the same aims are known (see Ref. [1,2]). Unfortunately, the Bosch space experiment was cancelled by the German Centre for Space and Avionics (DLR) in late 2000, since for organizational reasons the envisaged launch on the International Space Station ISS could not be realized. The setup of the experiment has been described in detail in Ref. [3]. 2.1. Results The results of the space experiment cover highfrequency measurements, thermal behaviour (Ref. [4]) and qualification status. Concerning highfrequency measurements, all devices fully operate as designed: • The low-noise amplifier in the cryogenic frontend exhibits a noise figure of better than 0.5 db at 77 K (3.4–4.2 GHz, gain 20 dB). • The input multiplexer fulfills the same electrical specifications as a conventional one (Fig. 1) and is also fully comparable regarding unloaded quality factors (12.000 at 77 K, trimming included). Therefore the advantage in mass and volume saving while maintaining the performance required is fully demonstrated.
Fig. 1. Electrical measurements of the three-channel input multiplexer.
• The dielectric resonators in the output multiplexer have unloaded quality factors of about 80.000 (including trimming) which is far superior to conventional technology. This results in a reduction of electrical losses and thus allows to decrease amplifier power. The qualification status of our space experiment is as according to qualifying-engineering status in space business. This means that the whole setup is fully qualified (Ref. [4]), from the single material and technology employed up to the whole system. Two results shall be mentioned here to illustrate the complexity of this work: • Superconducting devices have been fabricated, structurized, assembled and integrated on basis of specifications as in commercial programs. These specifications resulted from numerous tests (thermal cycling, vibration, destructive tests such as measurement of pulling forces, . . .) on a large number of samples (Fig. 2). • The cryogenic setup was designed to withstand mechanical vibrations as they occur when a spacecraft is launched (Fig. 3). The frame could withstand random vibrations with an acceleration of 20 g (rms). Furthermore, the mechanical transfer function was deduced and used as a basis for vibration qualifying of the highfrequency devices.
Fig. 2. Qualification sample: frame with mounted MIC test modules, the dark areas are half of 3 in. superconducting wafers with rows of contact pads.
T. K€asser et al. / Physica C 372–376 (2002) 489–492
Fig. 3. Setup of the Bosch space experiment: the cryogenic high-frequency devices are mounted on a plate which is suspended in a frame via Kevlar ropes.
To conclude, both qualification and electrical measurements were performed without any failure. Therefore we are sure that this setup would have passed the in-orbit demonstration with good success.
3. Future satellite payloads Our future development will be governed by two aspects: • Reduction of the cryogenic burden and hence improvement in overall mass, volume and power budget. There is ongoing and very promising work on films with higher Tc and thus higher operating temperature (Ref. [5]). • Improved superconducting devices, allowing for superior HF-performance (see following chapter). 3.1. Planar HTSC filters It is well known that planar HTSC filters are small in size and weight while offering extremely low high-frequency losses. To reach high-unloaded quality factors in planar designs, resonators have to be somewhat extended in space (a prominent example are disc resonators, Ref. [6]). Unfortu-
491
nately, these extended field patterns result for filters in long-range interactions deteriorating the filter performance (and imposing limits on achievable small bandwiths). Therefore, in realizing complex high-order filters as desired in satellite communications, one has often been satisfied with non-optimum losses. We are working on designs combining complexity and low-losses simultaneously. Our key to the problem is an optimization algorithm which optimizes coupling coefficients such that the resulting filter is as specified (Ref. [7]). The algorithm is extremely flexible and allows to introduce arbitrary couplings between arbitrary resonators. We regard a planar filter structure as described by two sets of couplings: one set are the designable couplings (designable by e.g. varying the distance between neighboured resonators), and the other set are the undesired but nevertheless present couplings. (Commonly, only the designable couplings are used in filter design.) We intend to use this algorithm by introducing the undesired crosscouplings as boundary conditions and by optimizing the designable couplings such that the overall set of couplings describe the filter specified. We have implemented the algorithm on a PC and we have optimized a set of coupling coefficients for a 12-pole filter in quasi-elliptic and self-equalized design according to common specifications for input multiplexers in satellite communications. The optimization procedure for this filter takes about 25 h, and the numerical precision for this filter order is to be noted. On the way towards realization of complex filters, we build low-order test structures to deduce values for the undesired cross-couplings. We have started by a dual-mode patch resonator (Fig. 4). Generally, such a structure is described only by the input and output couplings k0,l and k2,3 and the main coupling kl,2. We have used our optimization algorithm and by also allowing for crosscouplings k0,2 and k0,3 (representing coupling of energy from the ports two the non-neighboured mode and between the ports), we have achieved a much better fit to the measured data (Fig. 5). (It is also worth mentioning that this structure was realized on a Thallium-based film (fabricated at IPHT Jena, Germany) and measured at 85 K.)
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T. K€asser et al. / Physica C 372–376 (2002) 489–492
Acknowledgements
Fig. 4. Left: geometry of the dual-mode patch resonator employed as test structure (gray scale due to simulated current density); right: coupling schemes.
This work has been supported by the BMBF (German Federal Ministry for Education and Research) under grant 13N7390/2 and by the DLR (German Centre for Space and Avionics) under grants 50TT9833/3, 50YB9807/9 and 50Y9808. Numerous partners in the BMBF project have contributed to the results.
References
Fig. 5. Measurement of dual-mode patch resonator and fit with two different coupling schemes.
[1] M. Nisenoff, W. Meyers, IEEE Trans. Appl. Supercond. 11 (2001). [2] E. Polturak, G. Koren, I. Flohr, R. Waller, M. Guelman, IEEE Trans. Microwave Theory Tech. 48 (7) (2000) 1289– 1291. [3] M. Klauda, T. K€asser, B. Mayer, C. Neumann, F. Schnell, B. Aminov, A. Baumfalk, H. Chaloupka, S. Kolesov, H. Piel, N. Klein, S. Schornstein, M. Bareiss, IEEE Trans. Microwave Theory Tech. 48 (7) (2000) 1227–1239. [4] T. K€asser, M. Klauda, B. Mayer, C. Neumann, F. Schnell, U. Wochner, IEEE MTT-S Digest, Boston, June 2000. [5] H. Schneidewind, M. Manzel, K. Kirsch, IEEE Trans. Appl. Supercond. 11 (2001) 3106–3109. [6] H. Chaloupka, M. Jeck, B. Gurzinski, S. Kolesov, Electron. Lett. 32 (18) (1996) 1735–1736. [7] A.A. Atia, IEEE MTT-S International Microwave Symposium, Workshop on Microwave Filter Synthesis and Equivalent Circuit Extraction.
Superconductors and cryotechnology for space communications Tobias K€ asser a,*, Michael Viertel a, Ralf B€ olter a, Christian Neumann b, F. Schnell b a
b
Bosch SatCom GmbH, UC-RA/EMD, D-71501 Backnang, Germany Robert Bosch GmbH, Corporate Research and Development, D-70049 Stuttgart, Germany
Abstract In commercial satellite applications, superconductive devices offer the advantage of a reduction in mass and volume, combined with improved high-frequency performance. The Bosch space experiment clearly demonstrates these benefits, and it also shows the applicability of the technology with respect to space qualification procedure. Furthermore, this article describes improved design methods for planar superconducting filters, combining high Q-values with complex designs. 2002 Elsevier Science B.V. All rights reserved. Keywords: Cryogenics; Satellite communications; Filter design
1. Introduction One major application of high-temperature superconductivity is passive communication technology. The benefit of superconductivity and cryotechnology in space communications lies in the miniaturisation of communication systems as well as in improved performance with respect to e.g. selectivity or noise figure. In this contribution we will report on the status of the Bosch HTSC Space Experiment. The engineering-qualifying model clearly demonstrates the above mentioned advantages, and it is fully space-
*
Corresponding author. Tel.: +49-7191-930-1217; fax: +497191-930-1850. E-mail address: [email protected] (T. K€asser).
qualified with respect to typical commercial requirements. Furthermore, we will focus on our ongoing work which aims at a higher efficiency of cryogenic satellite payloads and at improved RF performance. We deal with problems arising when designing high-order filters combining complex designs and low electrical losses simultaneously.
2. Bosch space experiment It is the aim of the experiment to demonstrate the benefits of superconducting devices under real operating conditions. Furthermore, it is the aim to demonstrate the full applicability and qualificability of the materials involved, of all related assembly and integration techniques and of the
0921-4534/02/$ - see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 0 7 2 9 - 3
490
T. K€asser et al. / Physica C 372–376 (2002) 489–492
surrounding cryosystem. In space business, costumers are conservative, and a space experiment is a keystone in introducing a new technology into market. Other space experiments with the same aims are known (see Ref. [1,2]). Unfortunately, the Bosch space experiment was cancelled by the German Centre for Space and Avionics (DLR) in late 2000, since for organizational reasons the envisaged launch on the International Space Station ISS could not be realized. The setup of the experiment has been described in detail in Ref. [3]. 2.1. Results The results of the space experiment cover highfrequency measurements, thermal behaviour (Ref. [4]) and qualification status. Concerning highfrequency measurements, all devices fully operate as designed: • The low-noise amplifier in the cryogenic frontend exhibits a noise figure of better than 0.5 db at 77 K (3.4–4.2 GHz, gain 20 dB). • The input multiplexer fulfills the same electrical specifications as a conventional one (Fig. 1) and is also fully comparable regarding unloaded quality factors (12.000 at 77 K, trimming included). Therefore the advantage in mass and volume saving while maintaining the performance required is fully demonstrated.
Fig. 1. Electrical measurements of the three-channel input multiplexer.
• The dielectric resonators in the output multiplexer have unloaded quality factors of about 80.000 (including trimming) which is far superior to conventional technology. This results in a reduction of electrical losses and thus allows to decrease amplifier power. The qualification status of our space experiment is as according to qualifying-engineering status in space business. This means that the whole setup is fully qualified (Ref. [4]), from the single material and technology employed up to the whole system. Two results shall be mentioned here to illustrate the complexity of this work: • Superconducting devices have been fabricated, structurized, assembled and integrated on basis of specifications as in commercial programs. These specifications resulted from numerous tests (thermal cycling, vibration, destructive tests such as measurement of pulling forces, . . .) on a large number of samples (Fig. 2). • The cryogenic setup was designed to withstand mechanical vibrations as they occur when a spacecraft is launched (Fig. 3). The frame could withstand random vibrations with an acceleration of 20 g (rms). Furthermore, the mechanical transfer function was deduced and used as a basis for vibration qualifying of the highfrequency devices.
Fig. 2. Qualification sample: frame with mounted MIC test modules, the dark areas are half of 3 in. superconducting wafers with rows of contact pads.
T. K€asser et al. / Physica C 372–376 (2002) 489–492
Fig. 3. Setup of the Bosch space experiment: the cryogenic high-frequency devices are mounted on a plate which is suspended in a frame via Kevlar ropes.
To conclude, both qualification and electrical measurements were performed without any failure. Therefore we are sure that this setup would have passed the in-orbit demonstration with good success.
3. Future satellite payloads Our future development will be governed by two aspects: • Reduction of the cryogenic burden and hence improvement in overall mass, volume and power budget. There is ongoing and very promising work on films with higher Tc and thus higher operating temperature (Ref. [5]). • Improved superconducting devices, allowing for superior HF-performance (see following chapter). 3.1. Planar HTSC filters It is well known that planar HTSC filters are small in size and weight while offering extremely low high-frequency losses. To reach high-unloaded quality factors in planar designs, resonators have to be somewhat extended in space (a prominent example are disc resonators, Ref. [6]). Unfortu-
491
nately, these extended field patterns result for filters in long-range interactions deteriorating the filter performance (and imposing limits on achievable small bandwiths). Therefore, in realizing complex high-order filters as desired in satellite communications, one has often been satisfied with non-optimum losses. We are working on designs combining complexity and low-losses simultaneously. Our key to the problem is an optimization algorithm which optimizes coupling coefficients such that the resulting filter is as specified (Ref. [7]). The algorithm is extremely flexible and allows to introduce arbitrary couplings between arbitrary resonators. We regard a planar filter structure as described by two sets of couplings: one set are the designable couplings (designable by e.g. varying the distance between neighboured resonators), and the other set are the undesired but nevertheless present couplings. (Commonly, only the designable couplings are used in filter design.) We intend to use this algorithm by introducing the undesired crosscouplings as boundary conditions and by optimizing the designable couplings such that the overall set of couplings describe the filter specified. We have implemented the algorithm on a PC and we have optimized a set of coupling coefficients for a 12-pole filter in quasi-elliptic and self-equalized design according to common specifications for input multiplexers in satellite communications. The optimization procedure for this filter takes about 25 h, and the numerical precision for this filter order is to be noted. On the way towards realization of complex filters, we build low-order test structures to deduce values for the undesired cross-couplings. We have started by a dual-mode patch resonator (Fig. 4). Generally, such a structure is described only by the input and output couplings k0,l and k2,3 and the main coupling kl,2. We have used our optimization algorithm and by also allowing for crosscouplings k0,2 and k0,3 (representing coupling of energy from the ports two the non-neighboured mode and between the ports), we have achieved a much better fit to the measured data (Fig. 5). (It is also worth mentioning that this structure was realized on a Thallium-based film (fabricated at IPHT Jena, Germany) and measured at 85 K.)
492
T. K€asser et al. / Physica C 372–376 (2002) 489–492
Acknowledgements
Fig. 4. Left: geometry of the dual-mode patch resonator employed as test structure (gray scale due to simulated current density); right: coupling schemes.
This work has been supported by the BMBF (German Federal Ministry for Education and Research) under grant 13N7390/2 and by the DLR (German Centre for Space and Avionics) under grants 50TT9833/3, 50YB9807/9 and 50Y9808. Numerous partners in the BMBF project have contributed to the results.
References
Fig. 5. Measurement of dual-mode patch resonator and fit with two different coupling schemes.
[1] M. Nisenoff, W. Meyers, IEEE Trans. Appl. Supercond. 11 (2001). [2] E. Polturak, G. Koren, I. Flohr, R. Waller, M. Guelman, IEEE Trans. Microwave Theory Tech. 48 (7) (2000) 1289– 1291. [3] M. Klauda, T. K€asser, B. Mayer, C. Neumann, F. Schnell, B. Aminov, A. Baumfalk, H. Chaloupka, S. Kolesov, H. Piel, N. Klein, S. Schornstein, M. Bareiss, IEEE Trans. Microwave Theory Tech. 48 (7) (2000) 1227–1239. [4] T. K€asser, M. Klauda, B. Mayer, C. Neumann, F. Schnell, U. Wochner, IEEE MTT-S Digest, Boston, June 2000. [5] H. Schneidewind, M. Manzel, K. Kirsch, IEEE Trans. Appl. Supercond. 11 (2001) 3106–3109. [6] H. Chaloupka, M. Jeck, B. Gurzinski, S. Kolesov, Electron. Lett. 32 (18) (1996) 1735–1736. [7] A.A. Atia, IEEE MTT-S International Microwave Symposium, Workshop on Microwave Filter Synthesis and Equivalent Circuit Extraction.