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. Radio waves in this band have wavelengths from ten to one millimetre, giving it the name millimetre band or millimetre wave, sometimes abbreviated MMW or mmW.
Compared to lower bands, terrestrial radio signals in this band are extremely prone to atmospheric attenuation, making them of very little use over long distances. In particular, signals in the 57–64 GHz region are subject to a resonance of the oxygen molecule and are severely attenuated. Even over relatively short distances, rain fade is a serious problem, caused when absorption by rain reduces signal strength. In climates other than deserts absorption due to humidity also has an impact on propagation. While this absorption limits potential communications range, it also allows for smaller frequency reuse distances than lower frequencies. The small wavelength allows modest size antennas to have a small beam width, further increasing frequency reuse potential.
Read more about Extremely High Frequency: Propagation
Famous quotes containing the words extremely, high and/or frequency:
“‘Tis the perception of the beautiful,
A fine extension of the faculties,
Platonic, universal, wonderful,
Drawn from the stars, and filtered through the skies,
Without which life would be extremely dull.”
—George Gordon Noel Byron (1788–1824)
“Parents do not give up their children to strangers lightly. They wait in uncertain anticipation for an expression of awareness and interest in their children that is as genuine as their own. They are subject to ambivalent feelings of trust and competitiveness toward a teacher their child loves and to feelings of resentment and anger when their child suffers at her hands. They place high hopes in their children and struggle with themselves to cope with their children’s failures.”
—Dorothy H. Cohen (20th century)
“The frequency of personal questions grows in direct proportion to your increasing girth. . . . No one would ask a man such a personally invasive question as “Is your wife having natural childbirth or is she planning to be knocked out?” But someone might ask that of you. No matter how much you wish for privacy, your pregnancy is a public event to which everyone feels invited.”
—Jean Marzollo (20th century)