A Dielectric-Free Superconducting Coaxial Cable.

We have investigated the theoretical properties of a dielectric- free superconducting coaxial cable with a magnetically levitated inner conductor. We found that at 100 GHz the intrinsic attenuation along such a cable is on the order of .1 dB per kilometer. Furthermore, for a given cable, the loss is proportional to the square of the frequency. Thus, at 10GHz, one could expect losses on the order of 10 sup -3dB/km. This low loss coupled with a generous signal to noise ratio (approx 80dB at 100GHz bandwidth) helps provide bit rates of 100Gbit/sec over 600 kilometers. At 10Gbit/sec the distance increases to over 60,000 kilometers: more than twice the earth's circumference. 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 in excess of 10 sup 4 users could be supported. The two properties of superconductors central to this application are (1) very low intrinsic loss; and (2) expulsion of magnetic flux. Low loss allows high bandwidth dispersionless transmission. Magnetic flux expulsion permits magnetic support of the inner conductor thereby avoiding the large dielectric losses associated with any support material.