STI manufactures the SuperFilter™ system for cellular and PCS base stations (see About the Wireless Market). STI has successfully combined our superconductor circuits with complete cryogenic systems into a product that solves many of the pervasive problems facing the base station manufacturers and service providers of the wireless industry. Wireless communications base stations are limited by engineering trade-offs between interference performance, receiver sensitivity, and base station size. The SuperFilter™ offers excellent interference rejection and ultra-low noise figure in compact, practical packaging.
SuperFilter™ systems include thin-film superconductor filter microchips in protective packaging. The packaged filters and applicable LNAs (see Glossary), are mounted in a thermally-insulated enclosure, which in turn is mounted on a proprietary compact cryogenic cooler (see Cryogenic Coolers). This cryogenic unit, along with the controlling electronics, is fully-integrated into either a Tower Mount or Rack Mount platform.
Reducing Interference
Interference in wireless networks is caused by the intrusion of unwanted
signals from competing service provider's frequencies. For the mobile phone
user, interference causes cross talk and dropped calls, and prevents wireless
service providers from utilizing all of their available radio spectrum.
Thus interference can lead to lost revenue and unhappy customers.
The more channel selective a receiver filter can be, the less interference a service provider will experience. Near-zero RF (see Glossary) resistance is a fundamental physical advantage enjoyed by superconductors over any conventional material. In addition, STI incorporates advanced RF design and materials technology into SuperFilter™ systems. The result is much more selective and complex filters in narrow bandwidths, without compromising receiver sensitivity or size.
The World's Smallest Superconductor Filter System
STI believes it offers the smallest HTS filtering system in the wireless
industry. Filters are often located in the base station shelter of a cell
site (see About the Wireless
Market). Existing cell sites are often already filled with equipment
and conventional filters can comprise up to 30 percent of the space in
base stations. Many communities do not want unattractive towers with large
base stations in their backyard. As a result, cell sites are increasingly
expensive and site acquisition timing can have great uncertainty. In some
cases, suitable sites are not available within a reasonable time. Smaller
base stations improve the odds of acquiring new sites.
Equally important, existing network capacity is increasingly limited by space within fully-packed cell site shelters. For example, as cellular service providers begin to install new PCS network equipment, co-locating two systems in one base station will become increasingly desirable. Reducing base station hardware size provides more capacity and more options for service providers. Since filters can occupy 30 percent or more of base station system size in urban areas, smaller filters are essential to any size reduction.
SuperFilter™ systems are based on thin-film superconductor microchips - similar to those made of silicon. Thus the size of each filter is hundreds of times smaller than conventional filters. In addition, STI's Stirling cryogenic cooler is much more compact than other types of cryocoolers (see Cryogenic Coolers). Therefore, a complete system that is four to six times smaller than conventional urban cellular filters, and is significantly smaller than other demonstrated HTS offerings, provides relief for space-constrained base stations.
Expanding Base Station Coverage
The costs, delays and uncertainties caused by increased community resistance
to wireless infrastructure implementation are strongly motivating service
providers to more efficiently use existing cell sites. In addition, by
increasing the coverage area for each base station carriers require fewer
base stations to provide coverage for a given area, and less static for
the mobile phone user. With base station deployment costing as much as
$1 million per site and rising, reducing the number of base stations installed
results in substantial savings in capital investments.
The amount of noise picked up by a receiver filter, known as noise figure, is often the limiting factor in the coverage area of a base station. The SuperFilter™ system takes advantage of the very low insertion loss of the superconducting filter, the fact that both the filter and the LNA are operated at low temperatures and the reduction in noise that occurs by mounting the entire system on the tower. The SuperFilter™ can reduce noise figure by 2 decibels (dB) or more, from estimated conventional tower mount filter/LNA units. Tower mounting can offer an additional 2 dB benefit over ground mount units. STI believes the SuperFilter™ offers wireless service providers a reduction of as much as 30 percent in the number of cell sites required to cover the same area.