Extremely high frequency

Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low (or far) infrared light, also referred to as Terahertz radiation. This band has a wavelength of one to ten millimetres, giving it the name millimeter band or millimetre wave.

Radio signals in this band are extremely prone to atmospheric attenuation, making them of very little use over long distances. Even over relatively short distances, rain fade is a serious problem, caused when absorption by rain reduces signal strength.

Applications

This band is commonly used in radio astronomy.

In the United States, the band 38.6 - 40.0 GHz is used for licensed high-speed microwave data links, and the 60 GHz band can be used for unlicensed short range (1.7 km) data links with data throughputs up to 2.5 Gbit/s (gigabits per second). This is a civil air patrol frequency, as well. It is used commonly in flat terrain.

The 71-76, 81-86 and 92-95GHz bands are also used for point-to-point high-bandwidth communication links. These frequencies, as opposed to the 60GHz frequency, require a transmitting license in the US from the FCC, though do not suffer from the effects of oxygen absorption as the 60GHz does. There are plans for 10 GBit/s links using these frequencies as well. In the case of the 92-95GHz band, a 100MHz band has been reserved for space-borne radios, making this upper band limited to a transmission rate of only a few gigabits.

Applications include radar systems with high resolution. A recent development has been imagers for security applications as clothing and other organic materials are translucent in some mm-wave atmospheric windows.

See also

• Terahertz radiation
• Microwaves

External links

Academic

• Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).
• Millimetre-Wave Technology Group at Rutherford-Appleton Laboratory
• St. Andrews University mm-wave group
• A Survey of University Capabilities for a New Canadian Radio Telescope

Commercial

• QinetiQ mm-wave imager
• Roke manor research