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200 GHz Suggested for Last Mile Connections

I've focused on the demand for UHF TV broadcast spectrum in the main stories in this week's RF Report, but 200 GHz is where the high-speed action is.

A team of researchers at Karlsruhe Institute of Technology's Institute of Photonics and Quantum Electronics has demonstrated a 20 Gbps wireless data bridge operating at 220 GHz.

"For our experiment, we use state-of-the-art electronic up- and down-converter modules developed at the Fraunhofer IAF," said Igmar Kallfass, a researcher and the project's leader at the Fraunhofer Institute for Applied Solid State Physics." Previously, wireless data transmission at frequencies greater than 200 GHz with electronic up- and down-converters was virtually unexplored."

Kallfass noted that in the group's first indoor experiment, transmission distances were limited to 50 centimeters, but that has now been increased to 20 meters.

"The second wireless gateway performs the inverse operation of the first gateway by an electronic down-converter module," said Kallfass. "Eventually, the electrical signal is again encoded onto laser light and transmitted over the second fiber span."

While the data rate approaches that of free-space optical links, such links don't work--or only work with limited quality and stability--under adverse atmospheric conditions such as fog, rain, or dust. The millimeter wireless links are able to remain operational under such conditions.

It should be obvious to most readers that higher frequencies are needed for higher speed data. You don't hear much talk about using HF or even VHF frequencies for wireless broadband. I suspect that by the time the FCC is ready to auction of UHF TV broadcast spectrum—perhaps 10 years from now--wireless carriers will have realized that this relatively "low" frequency TV broadcast spectrum will be useful only for low bit-rate (by future standards) communications in rural areas where its range overcomes the disadvantage of limited data bandwidth. The intelligent wireless infrastructure for the next decade will be a robust fiber network feeding "last mile" wireless connections operating in the GHz region or perhaps for fixed links, even the millimeter region.