highest RF frequency?

what is the highest RF frequency ever used in a device? was it just experimental or it's being used? was it for communications purposes? I mean the highest radio frequency in microwave range, not the visible light!
thanks

Well, i know for radars that working in Ka band (nearly 40GHz).
There are type of rf tubes called Gyrotron which are capable to deliver continuous power over 1kw on frequencies over 300ghz. For similar purposes there are also reflexive triode.
For semiconductor devices, there are MHEMTs capable of working on frequencies over 200ghz. (I do not know any device which using them on that frequencies, so it might be that they are only experimental devices).

Today E-band radio links emerge for networking. They use up to 96 GHz. This is real commercial euipment around us. In the papers I read about 300GHz equipment.

http://users.erols.com/nspokes/300GHz.htm

Very interesting paper. I did not know that ham are trying so high frequencies. By the way, historically, ham discovered some bands. For example, HF communications were first developed by ham operators back in 20-ties. Then military guys took it to use.

Yes, a fascinating web page.
An oscillator tube called a "carcinotron"? What a great name, if you have dark sense of humor.

Related tidbit: Here's the United States Frequency Allocation Chart. It's very colorful.
The chart stops at 300 GHz. Above that point, the name changes from RF to infrared.
http://www.ntia.doc.gov/osmhome/allochrt.html

I did work on a radiometer that stopped just short of 200 GHz. Handling the waveguides was interesting. That is not quite at the 300 GHz cited above. I also spent considerable time with precision measurement tools and surface plates to get everything lined up. Radiation patterns were made on a compact range.

Beamwidths less than a degree from a parabola 5" in diameter gives one a new perspective.

One of the greatest amateur radio designing microwave stuff is Michael Kuhne DB6NT, the owner of KUHNE Electronic.

http://www.kuhne-electronic.de/en/3_Startpage

He was one of the first amateur in the world which did some experiments in 411 GHz.

In the first link very interesting the losses along the communication path

"Atmos Loss: 10.6 dB/km "

I'd like to know how affects the atmospherical conditions at these frequencies

The radiometer I mentioned above is intended to study temperature and water content in the atmosphere for weather prediction. Propagation loss/absdorption at various frequencies plays a part in the measurements.

Here is a snapshot of this particular instrument:
h**p://www.spacemart.com/reports/NG_Ships_First_Advanced_Tech_Microwave_Sounder_Fli ght_Instrument_To_NASA.html