7 (YBCO), at a critical temperature. The new filters are intended to increase basestation capacity and will deliver an improved quality of received signal.
The YBCO is deposited on to a 2in lanthanum aluminate substrate using a sputtering technique and etched using standard photolithography.
Superconductors have virtually no electrical resistance so signal losses and attenuations are significantly reduced. The use of YBCO also enables a filter with very sharp edges. The filter can be attached to the base of ground antennas, replacing current filters in a simple retrofit programme.
The superconductor filters are as much as 10 times the price of standard filters: the main cost lies with the cryogenic refrigeration required to maintain the superconductors' operating temperature.
Professor Ruggero Vaglio of Naples University said: "The cost will not be so much for the filter itself, it's the cryogenic cooler that's expensive. But the filter won't work without the cooler."
He believes that the price of the filter will not be prohibitive: "The filters could be as much as 10 times the cost of the filters currently used, but that is almost negligible against the cost of a basestation. The cost won't be the key limiting factor, but maintenance costs will be."
Prof Vaglio added that, in situations where signal quality is essential, the filter could be widely used: "In my opinion, the filter will be used in some special situations, for example in widely distributed basestations."
According to Prof Vaglio, the filters have been tested by Italian network provider Omnitel: "Most of the other similar systems currently being developed have only been tested in labs. Ours has been tested in the field, with very good results."