Super high frequency
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3 to 30 GHz |
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Super high frequency (or SHF) is the ITU designation for radio frequencies (RF) in the range of 3 GHz and 30 GHz. This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from ten to one centimetres. These frequencies fall within the microwave band, so radio waves with these frequencies are called microwaves. This frequency range is used for most radar transmitters, microwave ovens, wireless LANs, cell phones, satellite communication, microwave radio relay links, and numerous short range terrestrial data links. The commencing wireless USB technology will be using approximately 1/3 of this spectrum.
Frequencies in the SHF range are often referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations.
Propagation [edit]
Radio waves in the SHF range propagate entirely by line of sight; groundwave and skywave ("skip") propagation do not occur. Although in some cases they can penetrate building walls enough for useful reception, unobstructed rights of way cleared to the first Fresnel zone are usually required. Wavelengths are small enough that they can be focused into narrow beams by parabolic and horn antennas from a half meter to five meters in diameter. Therefore they are used in point-to-point terrestrial communications links limited by the visual horizon (about 40 miles). Such high gain antennas allow frequency reuse by nearby transmitters. The size of SHF waves allow large reflections from metal objects the size of automobiles, aircraft, and ships, and other vehicles. This, the narrow beamwidths possible with high gain antennas, and the low atmospheric attenuation as compared with higher frequencies make SHF frequencies very useful in radar. Attenuation and scattering by moisture in the atmosphere is a factor at the high end of the band.
Utilization [edit]
SHF frequencies occupy a "sweet spot" in the radio spectrum which is currently being exploited by many new radio services. They are the lowest frequency band where radio waves can be directed in narrow beams by conveniently sized antennas so they do not interfere with nearby transmitters on the same frequency, allowing frequency reuse. On the other hand, they are the highest frequencies which can be used for long distance terrestrial communication; higher frequencies in the EHF (millimeter wave) band are highly absorbed by the atmosphere, limiting practical propagation distances to one kilometer. The large bandwidth gives the band a very large information-carrying capacity. In recent decades many new solid state sources of microwave energy have been developed, and microwave integrated circuits for the first time allow significant signal processing to be done at these frequencies. Sources of EHF energy are much more limited and in an earlier state of development.
See also [edit]
External links [edit]
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ELF
3 Hz/100 Mm
30 Hz/10 Mm
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SLF
30 Hz/10 Mm
300 Hz/1 Mm
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ULF
300 Hz/1 Mm
3 kHz/100 km
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VLF
3 kHz/100 km
30 kHz/10 km
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LF
30 kHz/10 km
300 kHz/1 km
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MF
300 kHz/1 km
3 MHz/100 m
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HF
3 MHz/100 m
30 MHz/10 m
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VHF
30 MHz/10 m
300 MHz/1 m
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UHF
300 MHz/1 m
3 GHz/100 mm
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SHF
3 GHz/100 mm
30 GHz/10 mm
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EHF
30 GHz/10 mm
300 GHz/1 mm
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THF
300 GHz/1 mm
3 THz/0.1 mm
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