Toshiba has developed a tunable filter for wireless basestations that uses a high-temperature superconductor. It is designed to eliminate interference between applications using similar frequencies.
The superconductor tunable band-pass filter operates at around 2GHz. The filters are microstrip-line type, with a superconductor made of yttrium, barium, copper and oxygen (YBCO), grown on a dielectric substrate.
The device uses two filters, one for the top and the bottom of the required band edge. The tunability is achieved by mechanical control of the substrate.
The filters use a superconducting material because it minimises the filter loss, according to Hiroyuki Fuke, a senior engineer at Tosh-iba's R&D centre in Kawasaki.
"The filter loss is determined by the surface resistance. The surface resistance of the YBCO material in the microwave frequency region is more than two orders of magnitude lower than that of ordinary metal," he said.