A dielectric-free superconducting coaxial cable

The theoretical properties of a dielectric-free superconducting coaxial cable with a magnetically levitated inner conductor are studied. It is found that at 100 GHz the intrinsic attenuation along such a cable is on the order of a 0.1 dB per kilometer. Furthermore, for a given cable, the loss is proportional to the square of the frequency. This low loss, coupled with a generous signal to noise ratio (≈80 dB at 100-GHz bandwidth), provides bit rates of 100 Gb/s over 600 km. At 10 Gb/s the distance increases to over 60000 km. Such a high-bandwidth, extremely-low-loss electronic transmission medium might be of interest for very-long distance repeaterless communications. In addition, since efficient means of tapping coaxial media already exist, local area network applications with an excess of 10⁴ users could be supported. The two properties of superconductors central to this application are very low intrinsic loss and expulsion of magnetic flux. Low loss allows high-bandwidth dispersionless transmission, and magnetic flux expulsion permits magnetic support of the inner conductor, thereby avoiding the large dielectric losses associated with any support material