Research On High Temperature Superconductor Filters Used In Mobile Communication

The study of High Temperature Superconductor (HTS) filter systems has become a active field in the studies of superconductivity applications, due to its high performance and great commercial potential. In contrast with the conventional filters,HTS filters provided many advantages, such as much less insert loss, more steep edge, smaller size and easier integration. The installation of HTS filters in the front receivers of cellsites is ideal for reducing interference, saving frequency resources, expanding coverage, enhancing communicating quality and speeding transferring data. It also has promising application values in the field of spaceflight, secondary planet, communication and radar. At present, superconductor filter subsystems have been deployed abroad in the field of mobile communication and offered exceptional commercial performance.The design of HTS filters is a comprehensive problem of network analysis. According to the condition of calculation and practical size of superconducting films, we configured compacted forward-coupled microstrip filter, with the aid of TUMIC and SONNET software. The parameters of the filters are satisfying. Several important factors affecting the performance of filters were also studied and analyzed.During the fabricating of HTS filters, it is important that microstrip circuit connect with the outer. At present, we made Au or Ag contacts on the superconducting film in order to connect with the outer circuit. Because the contact resistance between the metal contacts and the superconducting films has large impact on the performance of superconducting filters, we experimental techniques. After annealing the optimum temperature and, we got the minimum contact resisitivity. We also further studied the interaction between Ag and YBCO films after annealing at a certain temperature and attempted to give an explanation and discussion.Packaging and jointing are another two important factors for the performance of HTS filters. Several issues that are crucial for HTS filters packaging and jointing are discussed in detail. Ultrasonic wire bonding was applied to connect the contacts and sub-miniature-A(SMA) connectors. Also a suitable shield box has been designed for the test of HTS filters.From designing to packing, and testing, the result is satisfying. The success of this experiment set up sound base for further study and development .Now our superconductor filter subsystems are experimenting in the cellsites.