High temperature superconducting filters-a maturing technology

The Defense Advanced Research Projects Agency (DARPA) has sponsored high temperature superconducting (HTS) technologies for many years. Much of the early work focused on materials, processing, patterning and designing of individual filters. The technology has since developed to the point where many systems have been designed and fielded for both government and commercial clients. The HTS filter elements have to be cooled into the 77 K range (~3/4 T_c), to become superconducting and electronically quiet. Cryogenic cooling is readily available using commercially available off the shelf coolers the military is currently using for FLIR (forward looking infrared) systems. This report discusses several HTS filter programs, their elements, and associated system performance benefits. The results of ground and flight tests of a superconducting filter system are presented. Improvements in many areas such as noise figure, S/N and range enhancement are demonstrated. The system improvements offered by the out of band rejection and low insertion loss are also significant