Super high frequency (SHF) is the

ITU The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Union ...

designation for radio frequencies (RF) in the range between 3 and 30

gigahertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...

(GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...

s range from one to ten centimetres. These frequencies fall within the

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...

band, so radio waves with these frequencies are called microwaves. The small wavelength of microwaves allows them to be directed in narrow beams by aperture antennas such as parabolic dishes and

horn antenna A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. They are ...

s, so they are used for point-to-point communication and data links This article from the beginning of the microwave era predicted the future value of microwaves for point-to-point communication. and for

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...

. This frequency range is used for most

transmitters,

wireless LAN A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office buildi ...

s, satellite communication,

microwave radio relay Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300MHz to 300GHz(1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signals are normally lim ...

links,

satellite phone A satellite telephone, satellite phone or satphone is a type of mobile phone that connects to other phones or the telephone network by radio through orbiting satellites instead of terrestrial cell sites, as cellphones do. The advantage of a sa ...

s (

S band The S band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a part of the microwave band of the electromagnetic spectrum covering frequencies from 2 to 4 gigahertz (GHz). Thus it crosses the conventi ...

), and numerous short range terrestrial data links. They are also used for heating in industrial microwave heating, medical

diathermy Diathermy is electrically induced heat or the use of high-frequency electromagnetic currents as a form of physical therapy and in surgical procedures. The earliest observations on the reactions of high-frequency electromagnetic currents upon the ...

, microwave hyperthermy to treat cancer, and to cook food in

microwave oven A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce ...

s. Frequencies in the SHF range are often referred to by their IEEE radar band designations: S, C, X, K_u, K, or K_a band, or by similar

NATO The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two N ...

or EU designations.

Propagation

Microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...

s propagate solely by line of sight; because of the small

refraction In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomen ...

due to their short wavelength, the groundwave and ionospheric reflection (

skywave In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature o ...

or "skip" propagation) seen with lower frequency radio waves 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 at microwave frequencies that the antenna can be much larger than a wavelength, allowing highly directional (high

gain Gain or GAIN may refer to: Science and technology * Gain (electronics), an electronics and signal processing term * Antenna gain * Gain (laser), the amplification involved in laser emission * Gain (projection screens) * Information gain in de ...

)

antenna Antenna ( antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two collid ...

s to be built which can produce narrow beams. Therefore, they are used in point-to-point terrestrial communications links, limited by the visual horizon to 30–40 miles (48–64 km). Such high gain antennas allow

frequency reuse A cellular network or mobile network is a communication network where the link to and from end nodes is wireless. The network is distributed over land areas called "cells", each served by at least one fixed-location transceiver (typically thr ...

by nearby transmitters. They are also used for communication with

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, ...

since the waves are not

refracted In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...

(bent) when passing through the

ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...

like lower frequencies. The

of SHF waves creates strong reflections from metal objects the size of automobiles, aircraft, and ships, and other vehicles. This and the narrow

beamwidth The beam diameter or beam width of an electromagnetic beam is the diameter along any specified line that is perpendicular to the beam axis and intersects it. Since beams typically do not have sharp edges, the diameter can be defined in many differ ...

s possible with high gain antennas and the low atmospheric attenuation as compared with higher frequencies make SHF the main frequencies used in

. Attenuation and scattering by moisture in the atmosphere increase with frequency, limiting the use of high SHF frequencies for long range applications. Small amounts of microwave energy are randomly scattered by water vapor molecules in the

troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. Fro ...

. This is used in

troposcatter Tropospheric scatter, also known as troposcatter, is a method of communicating with microwave radio signals over considerable distances – often up to and further depending on frequency of operation, equipment type, terrain, and climate facto ...

communications systems, operating at a few GHz, to communicate beyond the horizon. A powerful microwave beam is aimed just above the horizon; as it passes through the tropopause some of the microwaves are scattered back to Earth to a receiver beyond the horizon. Distances of 300 km can be achieved. These are mainly used for military communication.

Antennas

The

of SHF waves is short enough that efficient transmitting antennas are small enough to be conveniently mounted on handheld devices, so these frequencies are widely used for wireless applications. For example a quarter wave whip antenna for the SHF band is between 25 and 2.5 centimeters long.

Omnidirectional antenna In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis ( elevation angle), declining ...

s have been developed for applications like wireless devices and

cellphone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whi ...

s that are small enough to be enclosed inside the device's case. The main antenna used for these devices is the printed

inverted F antenna An inverted-F antenna is a type of antenna used in wireless communication, mainly at UHF and microwave frequencies. It consists of a monopole antenna running parallel to a ground plane and grounded at one end. The antenna is fed from an inte ...

(PIFA) consisting of a

monopole antenna A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, o ...

bent in an L shape, fabricated of copper foil on the

printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich str ...

inside the device. Small sleeve dipoles or quarter-wave monopoles are also used. The

patch antenna A patch antenna is a type of antenna with a low profile, which can be mounted on a surface. It consists of a planar rectangular, circular, triangular, or any geometrical sheet or "patch" of metal, mounted over a larger sheet of metal called a g ...

is another common type, often integrated into the skin of aircraft. The wavelengths are also small enough that SHF waves can be focused into narrow beams by high gain

directional antenna A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing increased performance and reduced interference from unwanted sources. Directional antennas provide increased performanc ...

s from a half meter to five meters in diameter. Directive antennas at SHF frequencies are mostly aperture antennas, such as

parabolic antenna A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or par ...

s (the most common type),

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...

slot Slot, the slot or Slots may refer to: People * Arne Slot (born 1978), Dutch footballer * Gerrie Slot (born 1954), Dutch cyclist * Hanke Bruins Slot (born 1977), Dutch politician * Tonny Bruins Slot (born 1947), Dutch association football coach ...

and

s. Large parabolic antennas can produce very narrow beams of a few degrees or less, and often must be aimed with the aid of a boresight. Another type of antenna practical at microwave frequencies is the

phased array In antenna theory, a phased array usually means an electronically scanned array, a computer-controlled array of antennas which creates a beam of radio waves that can be electronically steered to point in different directions without moving th ...

, consisting of many dipoles or

s on a flat surface, each fed through a

phase shifter A phase shift module is a microwave network module which provides a controllable phase shift of the RF signal. Phase shifters are used in phased arrays. Classification Active versus passive Active phase shifters provide gain, while passiv ...

, which allows the array's beam to be steered electronically. The short wavelength requires great mechanical rigidity in large antennas, to ensure that the radio waves arrive at the feed point in phase.

Waveguide

At microwave frequencies, the types of cable (

transmission line In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. The term applies when the conductors are long enough that the wave nature of the transmi ...

) used to conduct lower frequency radio waves, such as

coaxial cable Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...

, have high power losses. Therefore, to transport microwaves between the transmitter or receiver and the antenna with low losses, a special type of metal pipe called

waveguide A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...

must be used. Because of the high cost and maintenance requirements of long waveguide runs, in many microwave antennas the output stage of the transmitter or the RF front end of the receiver is located at the antenna.

Advantages

SHF frequencies occupy a "sweet spot" in the

radio spectrum The radio spectrum is the part of the electromagnetic spectrum with frequencies from 0 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particul ...

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 high frequency gives microwave communication links a very large information-carrying capacity ( bandwidth). In recent decades many new solid state sources of microwave energy have been developed, and microwave

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

s for the first time allow significant

signal processing Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing '' signals'', such as sound, images, and scientific measurements. Signal processing techniques are used to optimize transmissions, ...

to be done at these frequencies. Sources of EHF energy are much more limited and in an earlier state of development.

References

External links