Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgements
- 1 Superconductivity at microwave frequencies
- 2 Superconducting transmission lines
- 3 Superconducting cavity resonators
- 4 Microwave measurements
- 5 Superconducting filters
- 6 Superconducting delay lines
- 7 Superconducting antennas
- 8 Signal processing systems
- Appendix 1 The surface impedance of HTS materials
- Appendix 2 Substrates for superconductors
- Appendix 3 Some useful relations
- Index
2 - Superconducting transmission lines
Published online by Cambridge University Press: 14 September 2009
- Frontmatter
- Contents
- Preface
- Acknowledgements
- 1 Superconductivity at microwave frequencies
- 2 Superconducting transmission lines
- 3 Superconducting cavity resonators
- 4 Microwave measurements
- 5 Superconducting filters
- 6 Superconducting delay lines
- 7 Superconducting antennas
- 8 Signal processing systems
- Appendix 1 The surface impedance of HTS materials
- Appendix 2 Substrates for superconductors
- Appendix 3 Some useful relations
- Index
Summary
Introduction
In 1947 Pippard pointed out that a wave would be slowed when it propagated along a superconducting transmission line. This effect is due to the increase in inductance of the transmission line because of the penetration of the external magnetic field into the superconductor. The effect increases as the proportion of the magnetic field inside the superconductor increases relative to the proportion of the external magnetic field. This is not the only effect of using superconductors in transmission lines. Provided the transmission line propagates in a TEM mode, a superconducting transmission line is dispersionless, due to the penetration depth not varying with frequency. This is in contrast with a normal conductor where the skin depth is a function of frequency, and increasing the frequency has the effect of reducing the skin depth and hence increasing the velocity due to the decrease of internal inductance. However, for application purposes the most important effect of using superconductors is the very low loss of the transmission line.
This chapter looks at superconducting transmission lines in some detail. Section 2.2 considers the wide microstrip or parallel plate superconducting transmission line. This transmission line is one of the simplest and is close to the type of transmission line used in many applications. Because of its simple nature, the wide microstrip can be analysed and considerable understanding of the effects of using superconductors can be gained.
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- Publisher: Cambridge University PressPrint publication year: 1997