Microwave transmissionFrom Wikipedia, the free encyclopedia

The atmospheric attenuation ofmicrowaves in dry air with a precipitable water vapor level of 0.001 mm. The downward

spikes in the graph correspond to frequencies at which microwaves are absorbed more strongly, such as

by oxygenmolecules

Microwave transmission refers to the technology of transmitting information or energy by the use of radio

waves whose wavelengths are conveniently measured in small numbers of centimetre; these are

called microwaves. This part of the radio spectrum ranges acrossfrequencies of roughly 1.0 gigahertz (GHz) to

30 GHz. These correspond to wavelengths from 30 centimeters down to 1.0 cm.

Microwaves are widely used for point-to-point communications because their small wavelengthallows

conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving

antenna. This allows nearby microwave equipment to use the same frequencies without interfering with each

other, as lower frequency radio waves do. Another advantage is that the high frequency of microwaves gives

the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30 times

that of all the rest of the radio spectrum below it. A disadvantage is that microwaves are limited to line of

sightpropagation; they cannot pass around hills or mountains as lower frequency radio waves can.

Microwave radio transmission is commonly used in point-to-point communication systems on the surface of the

Earth, in satellite communications, and in deep space radio communications. Other parts of the microwave

radio band are used for radars, radio navigation systems, sensor systems, and radio astronomy.

The next higher part of the radio electromagnetic spectrum, where the frequencies are above 30 GHz and

below 100 GHz, are called "millimeter waves" because their wavelengths are conveniently measured in

millimeters, and their wavelengths range from 10 mm down to 3.0 mm. Radio waves in this band are usually

strongly attenuated by the Earthly atmosphere and particles contained in it, especially during wet weather.

Also, in wide band of frequencies around 60 GHz, the radio waves are strongly attenuated by molecular

oxygen in the atmosphere. The electronic technologies needed in the millimeter wave band are also much

more difficult to utilize than those of the microwave band.

Contents

  [hide] 

1 Uses

2 Parabolic (microwave) antenna

3 Microwave radio relay

o 3.1 How microwave radio relay links are formed

o 3.2 Planning considerations

o 3.3 Over-horizon microwave radio relay

o 3.4 Usage of microwave radio relay systems

o 3.5 Microwave link

3.5.1 Properties of microwave links

3.5.2 Uses of microwave links

4 Microwave power transmission

o 4.1 History

o 4.2 Common safety concerns

o 4.3 Proposed uses

o 4.4 Current status

5 See also

6 References

7 External links

[edit]Uses

Wireless transmission of information

One-way (e.g. television broadcasting) and two-way telecommunication using communications satellite

Terrestrial microwave radio broadcasting relay links in telecommunications networks including e.g.

backbone or backhaul carriers incellular networks linking BTS-BSC and BSC-MSC.

A parabolic antenna for Erdfunkstelle Raisting, based in Raisting, Bavaria, Germany.

C band horn-reflector antennas on the roof of a telephone switching center inSeattle, Washington, part of the U.S. AT&T

Long Lines microwave relay network.

Wireless transmission of power

Proposed systems e.g. for connecting solar power collecting satellites to terrestrial power grids

[edit]Parabolic (microwave) antenna

Main article: Parabolic antenna

To direct microwaves in narrow beams for point-to-point communication links or radiolocation (radar),

a parabolic antenna is usually used. This is an antenna that uses a parabolic reflector to direct the

microwaves. To achieve narrow beamwidths, the reflector must be much larger than the wavelength of the

radio waves. The relatively short wavelength of microwaves allows reasonably sized dishes to exhibit the

desired highly directional response for both receiving and transmitting.

[edit]Microwave radio relay

Dozens of microwave dishes on the Heinrich-Hertz-Turm in Germany.

Microwave radio relay is a technology for transmitting digital and analog signals, such as long-

distance telephone calls, television programs, and computer data, between two locations on a line of

sight radio path. In microwave radio relay, microwaves are transmitted between the two locations

with directional antennas, forming a fixed radio connection between the two points. The requirement of a line of

sight limits the distance between stations to 30 or 40 miles.

Beginning in the 1950s and 1960s networks of microwave relay links, such as the AT&T Long Lines system in

the U.S., carried long distance telephone calls and television programs between cities. These included

long daisy-chained series of such links that traversed mountain ranges and spanned continents. Much of the

transcontinental traffic is now carried by cheaperoptical fibers and communication satellites, but microwave

relay remains important for shorter distances.

[edit]How microwave radio relay links are formed

Relay towers on Frazier Mountain,Southern California

Because the radio waves travel in narrow beams confined to a line-of-sight path from one antenna to the other,

they don't interfere with other microwave equipment, and nearby microwave links can use the same

frequencies. Antennas used must be highly directional (Highgain); these antennas are installed in elevated

locations such as large radio towers in order to be able to transmit across long distances. Typical types of

antenna used in radio relay link installations are parabolic antennas, dielectric lens, and horn-reflector

antennas|, which have a diameter of up to 4 meters. Highly directive antennas permit an economical use of the

available frequency spectrum, despite long transmission distances.

Danish military radio relay node

[edit]Planning considerations

Because of the high frequencies used, a quasi-optical line of sight between the stations is generally required.

Additionally, in order to form the line of sight connection between the two stations, the first Fresnel zone must

be free from obstacles so the radio waves can propagateacross a nearly uninterrupted path. Obstacles in the

signal field cause unwanted attenuation, and are as a result only acceptable in exceptional cases. High

mountain peak or ridge positions are often ideal: Europe's highest radio relay station, the Richtfunkstation

Jungfraujoch, is situated atop the Jungfraujoch ridge at an altitude of 3,705 meters (12,156 ft) above sea level.

Multiple antennas provide space diversity

Obstacles, the curvature of the Earth, the geography of the area and reception issues arising from the use of

nearby land (such as in manufacturing and forestry) are important issues to consider when planning radio links.

In the planning process, it is essential that "path profiles" are produced, which provide information about

the terrain andFresnel zones affecting the transmission path. The presence of a water surface, such as a lake

or river, in the mid-path region also must be taken into consideration as it can result in a near-perfect reflection

(even modulated by wave or tide motions), creatingmultipath distortion as the two received signals ("wanted"

and "unwanted") swing in and out of phase. Multipath fades are usually deep only in a small spot and a narrow

frequency band, so space and/or frequency diversity schemes would be applied to mitigate these effects.

The effects of atmospheric stratification cause the radio path to bend downward in a typical situation so a major

distance is possible as the earth equivalent curvature increases from 6370 km to about 8500 km (a 4/3

equivalent radius effect). Rare events of temperature, humidity and pressure profile versus height, may

produce large deviations and distortion of the propagation and affect transmission quality. High intensity rain

and snow must also be considered as an impairment factor, especially at frequencies above 10 GHz. All

previous factors, collectively known as path loss, make it necessary to compute suitable power margins, in

order to maintain the link operative for a high percentage of time, like the standard 99.99% or 99.999% used in

'carrier class' services of most telecommunication operators.

The longest microwave radio relay known up to date cross the Red Sea with 360km hop between Jebel Erba

(2170m a.s.l., 20°44'46.17"N 36°50'24.65"E, Sudan) and Jebel Dakka (2572m a.s.l., 21° 5'36.89"N

40°17'29.80"E , Saudi Arabia). The link built in 1979 by Telettra allowed to proper transmit 300 telephone

channels and 1 TV signal, in the 2GHz frequency band. [1]

Portable microwave rig for Electronic news gathering (ENG) for television news

[edit]Over-horizon microwave radio relay

In over-horizon, or tropospheric scatter, microwave radio relay, unlike a standard microwave radio relay link,

the sending and receiving antennas do not use a line of sight transmission path. Instead, the stray signal

transmission, known as "tropo - scatter" or simply "scatter," from the sent signal is picked up by the receiving

station. Signal clarity obtained by this method depends on the weather and other factors, and as a result a high

level of technical difficulty is involved in the creation of a reliable over horizon radio relay link. Over horizon

radio relay links are therefore only used where standard radio relay links are unsuitable (for example, in

providing a microwave link to an island).

[edit]Usage of microwave radio relay systems

During the 1950s the AT&T Long Lines system of microwave relay links grew to carry the majority of US long

distance telephone traffic, as well as intercontinental television networksignals.[1] The prototype was called TDX

and was tested with a connection between New York City and Murray Hill, the location of Bell Laboratories in

1946. The TDX system was set up between New York and Boston in 1947. The TDX was improved to the TD2,

which still usedklystron tubes in the transmitters, and then later to the TD3 that used solid state electronics. The

main motivation in 1946 to use microwave radio instead of cable was that a large capacity could be installed

quickly and at less cost. It was expected at that time that the annual operating costs for microwave radio would

be greater than for cable. There were two main reasons that a large capacity had to be introduced suddenly:

Pent up demand for long distance telephone service, because of the hiatus during the war years, and the new

medium of television, which needed more bandwidth than radio.

Similar systems were soon built in many countries, until the 1980s when the technology lost its share of fixed

operation to newer technologies such as fiber-optic cable and communication satellites, which offer lower cost

per bit.

At the turn of the century, microwave radio relay systems are being used increasingly in portable radio

applications. The technology is particularly suited to this application because of lower operating costs, a more

efficient infrastructure, and provision of direct hardware access to the portable radio operator.

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[edit]Microwave link

A microwave link is a communications system that uses a beam of radio waves in the microwave frequency

range to transmit video, audio, or data between two locations, which can be from just a few feet or meters to

several miles or kilometers apart. Microwave links are commonly used by television broadcasters to transmit

programmes across a country, for instance, or from an outside broadcast back to a studio.

Mobile units can be camera mounted, allowing cameras the freedom to move around without trailing cables.

These are often seen on the touchlines of sports fields on Steadicam systems.

[edit]Properties of microwave links

Involve line of sight (LOS) communication technology

Affected greatly by environmental constraints, including rain fade

Have very limited penetration capabilities through obstacles such as hills, buildings and trees

Sensitive to high pollen count[citation needed]

Signals can be degraded[citation needed]during Solar proton events [2]

[edit]Uses of microwave links

In communications between satellites and base stations

As backbone carriers for cellular systems

In short range indoor communications

Telecommunications, in linking remote and regional telephone exchanges to larger (main) exchanges

without the need for copper/optical fibre lines.

[edit]Microwave power transmission

Microwave power transmission (MPT) is the use of microwaves to transmit power through outer space or

the atmosphere without the need for wires. It is a sub-type of the more general wireless energy

transfer methods.

[edit]History

Following World War II, which saw the development of high-power microwave emitters known as cavity

magnetrons, the idea of using microwaves to transmit power was researched. In 1964, William C.

Brown demonstrated a miniature helicopter equipped with a combination antenna and rectifier device called

a rectenna. The rectenna converted microwave power into electricity, allowing the helicopter to fly.[3] In

principle, the rectenna is capable of very high conversion efficiencies - over 90% in optimal circumstances.

Most proposed MPT systems now usually include a phased array microwave transmitter. While these have

lower efficiency levels they have the advantage of being electrically steered using no moving parts, and are

easier to scale to the necessary levels that a practical MPT system requires.

Using microwave power transmission to deliver electricity to communities without having to build cable-based

infrastructure is being studied at Grand Bassin on Reunion Island in the Indian Ocean.

Microwave spying

During the Cold War, the US intelligence agencies, such as NSA, were reportedly able to intercept Soviet

microwave messages using satellites such as Rhyolite.[4] Microwave also used in mobile communication.

[edit]Common safety concerns

The common reaction to microwave transmission is one of concern, as microwaves are generally perceived by

the public as dangerous forms of radiation - stemming from the fact that they are used in microwave ovens.

While high power microwaves can be painful and dangerous as in the United States Military's Active Denial

System, MPT systems are generally proposed to have only low intensity at the rectenna.

Though this would be extremely safe as the power levels would be about equal to the leakage from a

microwave oven, and only slightly more than a cell phone, the relatively diffuse microwave beam necessitates a

large rectenna area for a significant amount of energy to be transmitted.

Research has involved exposing multiple generations of animals to microwave radiation of this or higher

intensity, and no health issues have been found.[5]

[edit]Proposed uses

Main article: Solar power satellite

MPT is the most commonly proposed method for transferring energy to the surface of the Earth from solar

power satellites or other in-orbit power sources. MPT is occasionally proposed for the power supply in [beam-

powered propulsion] for orbital lift space ships. Even though lasers are more commonly proposed, their low

efficiency in light generation and reception has led some designers to opt for microwave based systems.

[edit]Current status

Wireless Power Transmission (using microwaves) is well proven. Experiments in the tens of kilowatts have

been performed at Goldstone in California in 1975[6][7][8] and more recently (1997) at Grand Bassin on Reunion

Island.[9] In 2008 a long range transmission experiment successfully transmitted 20 watts 92 miles (148 km)

from a mountain on Maui to the main island of Hawaii.[10]

[edit]See also

energy portal

Wireless energy transfer

Fresnel zone

Passive repeater

Radio repeater

Transmitter station

Path loss

British Telecom microwave network

Trans-Canada Microwave

Antenna array (electromagnetic)

[edit]References

1. ̂  "Sugar Scoop Antennas Capture Microwaves." Popular Mechanics, February 1985, p. 87, bottom of page.

2. ̂  Analyzing Microwave Spectra Collected by the Solar Radio Burst Locator

3. ̂  EXPERIMENTAL AIRBORNE MICROWAVE SUPPORTED PLATFORM Descriptive Note : Final rept. Jun

64-Apr 65

4. ̂  James Bamford, The Shadow Factory, Doubleday, 2008, p 176

5. ̂  Environmental Effects - the SPS Microwave Beam

6. ̂  NASA Video, date/author unknown

7. ̂  Wireless Power Transmission for Solar Power Satellite (SPS) (Second Draft by N. Shinohara), Space

Solar Power Workshop, Georgia Institute of Technology

8. ̂  Brown., W. C. (September 1984). "The History of Power Transmission by Radio Waves". Microwave

Theory and Techniques, IEEE Transactions on (Volume: 32, Issue: 9 On page(s): 1230- 1242 + ISSN:

0018-9480). DOI:10.1109/TMTT.1984.1132833.

9. ̂  POINT-TO-POINT WIRELESS POWER TRANSPORTATION IN REUNION ISLAND 48th International

Astronautical Congress, Turin, Italy, 6–10 October 1997 - IAF-97-R.4.08 J. D. Lan Sun Luk, A. Celeste, P.

Romanacce, L. Chane Kuang Sang, J. C. Gatina - University of La Réunion - Faculty of Science and

Technology.

10. ̂  http://www.wired.com/wiredscience/2008/09/visionary-beams/

Microwave Radio Transmission Design Guide, Trevor Manning, Artech House, 1999

MicrowaveFrom Wikipedia, the free encyclopedia

This article is about the electromagnetic wave. For the cooking appliance, see Microwave oven. For other uses,

see Microwaves (disambiguation).

A microwave telecommunications tower on Wrights Hill in Wellington, New Zealand

Microwaves are radio waves with wavelengths ranging from as long as one meter to as short as one

millimetre, or equivalently, withfrequencies between 300 MHz (0.3 GHz) and 300 GHz.[1] This broad definition

includes both UHF and EHF (millimeter waves), and various sources use different boundaries.[2] In all cases,

microwave includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often

putting the lower boundary at 1 GHz (30 cm), and the upper around 100 GHz (3 mm).

Apparatus and techniques may be described qualitatively as "microwave" when the wavelengths of signals are

roughly the same as the dimensions of the equipment, so that lumped-element circuit theory is inaccurate. As a

consequence, practical microwave technique tends to move away from the discrete resistors, capacitors,

and inductors used with lower-frequency radio waves. Instead, distributed circuit elements and transmission-

line theory are more useful methods for design and analysis. Open-wire and coaxial transmission lines give

way to waveguides and stripline, and lumped-element tuned circuits are replaced by cavity resonators or

resonant lines. Effects of reflection,polarization, scattering, diffraction, and atmospheric absorption usually

associated with visible light are of practical significance in the study of microwave propagation. The

same equations of electromagnetic theory apply at all frequencies.

The prefix "micro-" in "microwave" is not meant to suggest a wavelength in the micrometer range. It indicates

that microwaves are "small" compared to waves used in typical radio broadcasting, in that they have shorter

wavelengths. The boundaries between far infrared light,terahertz radiation, microwaves, and ultra-high-

frequency radio waves are fairly arbitrary and are used variously between different fields of study.

Electromagnetic waves longer (lower frequency) than microwaves are called "radio waves". Electromagnetic

radiation with shorter wavelengths may be called "millimeter waves", terahertz radiation or even T-rays.

Definitions differ for millimeter wave band, which the IEEE defines as 110 GHz to 300 GHz.

Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is in

effect opaque, until the atmosphere becomes transparent again in the so-called infrared and optical

window frequency ranges.

Light comparison

Name Wavelength Frequency (Hz) Photon Energy (eV)

Gamma ray less than 0.01 nm more than 10 EHz 100 keV – 300+ GeV

X-Ray 0.01 to 10 nm 30 EHz – 30 PHz 120 eV to 120 keV

Ultraviolet 10 nm – 400 nm 30 PHz – 790 THz 3 eV to 124 eV

Visible 390 nm – 750 nm 790 THz – 405 THz 1.7 eV – 3.3 eV

Infrared 750 nm – 1 mm 405 THz – 300 GHz 1.24 meV – 1.7 eV

Microwave

1 mm – 1 meter300 GHz – 300 MHz

1.24 µeV – 1.24 meV

Radio 1 mm – 100,000 km 300 GHz – 3 Hz 12.4 feV – 1.24 meV

Contents

  [hide] 

1 Microwave sources

2 Uses

o 2.1 Communication

o 2.2 Radar

o 2.3 Radio astronomy

o 2.4 Navigation

o 2.5 Power

o 2.6 Spectroscopy

3 Microwave frequency bands

4 Microwave frequency measurement

5 Health effects

6 History and research

7 See also

8 References

9 External links

[edit]Microwave sources

High-power microwave sources use specialized vacuum tubes to generate microwaves. These devices operate

on different principles from low-frequency vacuum tubes, using the ballistic motion of electrons in a vacuum

under the influence of controlling electric or magnetic fields, and include the magnetron (used in microwave

ovens), klystron, traveling-wave tube (TWT), and gyrotron. These devices work in the density modulated mode,

rather than the current modulated mode. This means that they work on the basis of clumps of electrons flying

ballistically through them, rather than using a continuous stream of electrons.

Cutaway view inside a cavity magnetronas used in a microwave oven

Low-power microwave sources use solid-state devices such as the field-effect transistor (at least at lower

frequencies), tunnel diodes,Gunn diodes, and IMPATT diodes.[3]

A maser is a device similar to a laser, which amplifies light energy by stimulating photons. The maser, rather

than amplifying light energy, amplifies the lower frequency, longer wavelength microwaves and radio frequency

emissions.

The sun also emits microwave radiation, although most of it is blocked by Earth's atmosphere.[4][not in citation given]

The Cosmic Microwave Background Radiation (CMBR) is a source of microwaves that supports the science

of cosmology's Big Bangtheory of the origin of the Universe.

[edit]Uses

Stripline techniques become increasingly necessary at higher frequencies

[edit]Communication

Before the advent of fiber-optic transmission, most long-distance telephone calls were carried via networks

of microwave radio relay links run by carriers such as AT&T Long Lines. Starting in the early 1950s, frequency

division multiplex was used to send up to 5,400 telephone channels on each microwave radio channel, with as

many as ten radio channels combined into one antenna for the hop to the next site, up to 70 km away.

Wireless LAN protocols, such as Bluetooth and the IEEE 802.11 specifications, also use microwaves in the

2.4 GHz ISM band, although802.11a uses ISM band and U-NII frequencies in the 5 GHz range. Licensed long-

range (up to about 25 km) Wireless Internet Access services have been used for almost a decade in many

countries in the 3.5–4.0 GHz range. The FCC recently[when?] carved out spectrum for carriers that wish to offer

services in this range in the U.S. — with emphasis on 3.65 GHz. Dozens of service providers across the

country are securing or have already received licenses from the FCC to operate in this band. The WIMAX

service offerings that can be carried on the 3.65 GHz band will give business customers another option for

connectivity.

Metropolitan area network (MAN) protocols, such as WiMAX (Worldwide Interoperability for Microwave Access)

are based on standards such as IEEE 802.16, designed to operate between 2 to 11 GHz. Commercial

implementations are in the 2.3 GHz, 2.5 GHz, 3.5 GHz and 5.8 GHz ranges.

Mobile Broadband Wireless Access (MBWA) protocols based on standards specifications such as IEEE

802.20 or ATIS/ANSI HC-SDMA(such as iBurst) operate between 1.6 and 2.3 GHz to give mobility and in-

building penetration characteristics similar to mobile phones but with vastly greater spectral efficiency.[5]

Some mobile phone networks, like GSM, use the low-microwave/high-UHF frequencies around 1.8 and

1.9 GHz in the Americas and elsewhere, respectively. DVB-SH and S-DMB use 1.452 to 1.492 GHz, while

proprietary/incompatible satellite radio in the U.S. uses around 2.3 GHz for DARS.

Microwave radio is used in broadcasting and telecommunication transmissions because, due to their short

wavelength, highly directional antennas are smaller and therefore more practical than they would be at longer

wavelengths (lower frequencies). There is also more bandwidth in the microwave spectrum than in the rest of

the radio spectrum; the usable bandwidth below 300 MHz is less than 300 MHz while many GHz can be used

above 300 MHz. Typically, microwaves are used in television news to transmit a signal from a remote location

to a television station from a specially equipped van. See broadcast auxiliary service (BAS), remote pickup

unit (RPU), and studio/transmitter link (STL).

Most satellite communications systems operate in the C, X, Ka, or Ku bands of the microwave spectrum. These

frequencies allow large bandwidth while avoiding the crowded UHF frequencies and staying below the

atmospheric absorption of EHF frequencies. Satellite TV either operates in the C band for the traditional large

dish fixed satellite service or Kuband for direct-broadcast satellite. Military communications run primarily over X

or Ku-band links, with Ka band being used for Milstar.

[edit]Radar

Radar uses microwave radiation to detect the range, speed, and other characteristics of remote objects.

Development of radar was accelerated during World War II due to its great military utility. Now radar is widely

used for applications such as air traffic control, weather forecasting, navigation of ships, and speed

limit enforcement.

A Gunn diode oscillator and waveguide are used as a motion detector for automatic door openers.

[edit]Radio astronomy

Most radio astronomy uses microwaves. Usually the naturally-occurring microwave radiation is observed, but

active radar experiments have also been done with objects in the solar system, such as determining the

distance to the Moon or mapping the invisible surface of Venus through cloud cover.

Galactic background radiation of the Big Bang mapped with increasing resolution

[edit]Navigation

Global Navigation Satellite Systems (GNSS) including the Chinese Beidou, the American Global Positioning

System (GPS) and the Russian GLONASS broadcast navigational signals in various bands between about

1.2 GHz and 1.6 GHz.

[edit]Power

A microwave oven passes (non-ionizing) microwave radiation (at a frequency near 2.45 GHz) through food,

causing dielectric heatingprimarily by absorption of the energy in water. Microwave ovens became common

kitchen appliances in Western countries in the late 1970s, following development of inexpensive cavity

magnetrons. Water in the liquid state possesses many molecular interactions that broaden the absorption peak.

In the vapor phase, isolated water molecules absorb at around 22 GHz, almost ten times the frequency of the

microwave oven.

Microwave heating is used in industrial processes for drying and curing products.

Many semiconductor processing techniques use microwaves to generate plasma for such purposes as reactive

ion etching and plasma-enhanced chemical vapor deposition(PECVD).

Microwave frequencies typically ranging from 110 – 140 GHz are used in stellarators and more notably

in tokamak experimental fusion reactors to help heat the fuel into a plasma state. The

upcoming ITER Thermonuclear Reactor[6] is expected to range from 110–170 GHz and will employ Electron

Cyclotron Resonance Heating (ECRH).[7]

Microwaves can be used to transmit power over long distances, and post-World War II research was done to

examine possibilities. NASA worked in the 1970s and early 1980s to research the possibilities of using solar

power satellite (SPS) systems with large solar arrays that would beam power down to the Earth's surface via

microwaves.

Less-than-lethal weaponry exists that uses millimeter waves to heat a thin layer of human skin to an intolerable

temperature so as to make the targeted person move away. A two-second burst of the 95 GHz focused beam

heats the skin to a temperature of 130 °F (54 °C) at a depth of 1/64th of an inch (0.4 mm). The United States

Air Force and Marines are currently using this type of active denial system.[8]

[edit]Spectroscopy

Microwave radiation is used in electron paramagnetic resonance (EPR or ESR) spectroscopy, typically in the

X-band region (~9 GHz) in conjunction typically with magnetic fields of 0.3 T. This technique provides

information on unpaired electrons in chemical systems, such as free radicals or transition metal ions such as

Cu(II). The microwave radiation can also be combined with electrochemistry as in microwave enhanced

electrochemistry.

[edit]Microwave frequency bands

The microwave spectrum is usually defined as electromagnetic energy ranging from approximately 1 GHz to

100 GHz in frequency, but older usage includes lower frequencies. Most common applications are within the 1

to 40 GHz range. One set of microwave frequency bands designations by the Radio Society of Great

Britain (RSGB), is tabulated below:

ITU Radio Band Numbers

1 2 3 4 5 6 7 8 9 10 11 12

ITU Radio Band Symbols

ELF SLF ULF VLF LF MF HF VHF UHF SHF EHF THF

NATO Radio bands

A B C D E F G H I J K L M

IEEE Radar bands

HF VHF UHF L S C X Ku K Ka Q V W D

v d e

Microwave frequency bands

Letter Designation Frequency range

L band 1 to 2 GHz

S band 2 to 4 GHz

C band 4 to 8 GHz

X band 8 to 12 GHz

Ku band 12 to 18 GHz

K band 18 to 26.5 GHz

Ka band 26.5 to 40 GHz

Q band 33 to 50 GHz

U band 40 to 60 GHz

V band 50 to 75 GHz

E band 60 to 90 GHz

W band 75 to 110 GHz

F band 90 to 140 GHz

D band 110 to 170 GHz

P band is sometimes used for Ku Band. "P" for "previous" was a radar band used in the UK ranging from 250 to

500 MHz and now obsolete per IEEE Std 521, see [9] and.[10] For other definitions see Letter Designations of

Microwave Bands.

When radars were first developed at K band during World War II, it was not realized that there was a nearby

absorption band (due to water vapor and oxygen at the atmosphere). To avoid this problem, the original K band

was split into a lower band, Ku, and upper band, Ka see.[11]

[edit]Microwave frequency measurement

Microwave frequency can be measured by either electronic or mechanical techniques.

Frequency counters or high frequency heterodyne systems can be used. Here the unknown frequency is

compared with harmonics of a known lower frequency by use of a low frequency generator, a harmonic

generator and a mixer. Accuracy of the measurement is limited by the accuracy and stability of the reference

source.

Mechanical methods require a tunable resonator such as an absorption wavemeter, which has a known relation

between a physical dimension and frequency.

Wavemeter for measuring in the Ku band

In a laboratory setting, Lecher lines can be used to directly measure the wavelength on a transmission line

made of parallel wires, the frequency can then be calculated. A similar technique is to use a

slotted waveguide or slotted coaxial line to directly measure the wavelength. These devices consist of a probe

introduced into the line through a longitudinal slot, so that the probe is free to travel up and down the line.

Slotted lines are primarily intended for measurement of the voltage standing wave ratio on the line. However,

provided astanding wave is present, they may also be used to measure the distance between the nodes, which

is equal to half the wavelength. Precision of this method is limited by the determination of the nodal locations.

[edit]Health effects

Further information: Electromagnetic radiation and health and Microwave burn

Microwaves do not contain sufficient energy to chemically change substances by ionization, and so are an

example of nonionizingradiation. The word "radiation" refers to energy radiating from a source and not

to radioactivity. It has not been shown conclusively that microwaves (or other nonionizing electromagnetic

radiation) have significant adverse biological effects at low levels. Some, but not all, studies suggest that long-

term exposure may have a carcinogenic effect.[12] This is separate from the risks associated with very high

intensity exposure, which can cause heating and burns like any heat source, and not a unique property of

microwaves specifically.

During World War II, it was observed that individuals in the radiation path of radar installations experienced

clicks and buzzing sounds in response to microwave radiation. This microwave auditory effect was thought to

be caused by the microwaves inducing an electric current in the hearing centers of the brain.[13] Research

by NASA in the 1970s has shown this to be caused by thermal expansion in parts of the inner ear.

When injury from exposure to microwaves occurs, it usually results from dielectric heating induced in the body.

Exposure to microwave radiation can produce cataracts by this mechanism, because the microwave heating

denatures proteins in the crystalline lens of the eye (in the same way that heat turns egg whites white and

opaque). The lens and cornea of the eye are especially vulnerable because they contain no blood vessels that

can carry away heat. Exposure to heavy doses of microwave radiation (as from an oven that has been

tampered with to allow operation even with the door open) can produce heat damage in other tissues as well,

up to and including serious burns that may not be immediately evident because of the tendency for microwaves

to heat deeper tissues with higher moisture content.

[edit]History and research

The existence of radio waves was predicted by James Clerk Maxwell in 1864 from his equations. In

1888, Heinrich Hertz was the first to demonstrate the existence of radio waves by building a spark gap radio

transmitter that produced 450 MHz microwaves, in the UHF region. The equipment he used was primitive,

including a horse trough, a wrought iron point spark, and Leyden jars. He also built the first parabolic antenna,

using a zinc gutter sheet. In 1894 Indian radio pioneer Jagdish Chandra Bose publicly demonstrated radio

control of a bell using millimeter wavelengths, and conducted research into the propagation of microwaves.[14]

Perhaps the first, documented, formal use of the term microwave occurred in 1931:

"When trials with wavelengths as low as 18 cm were made known, there was undisguised surprise that

the problem of the micro-wave had been solved so soon." Telegraph & Telephone Journal XVII. 179/1

In 1943, the Hungarian engineer Zoltán Bay sent ultra-short radio waves to the moon, which, reflected

from there, worked as a radar, and could be used to measure distance, as well as to study the moon.[15]

Perhaps the first use of the word microwave in an astronomical context occurred in 1946 in an article

"Microwave Radiation from the Sun and Moon" by Robert Dicke and Robert Beringer. This same article

also made a showing in the New York Times issued in 1951.

In the history of electromagnetic theory, significant work specifically in the area of microwaves and their

applications was carried out by researchers including:

Specific work on microwaves

Work carried out by Area of work

Barkhausen and Kurz Positive grid oscillators

Hull Smooth bore magnetron

Varian BrothersVelocity modulated electron beam → klystron tube

Randall and Boot Cavity magnetron

Electromagnetic spectrum with visible light highlighted

[edit]See also

Block upconverter  (BUC)

Cosmic microwave background radiation

Electron cyclotron resonance

International Microwave Power Institute

Low-noise block converter  (LNB)

Maser

Microwave transmission

Microwave chemistry

Microwave auditory effect

Microwave cavity

Microwave radio relay

Orthomode transducer  (OMT)

Plasma-enhanced chemical vapour deposition

Rain fade

RF switch matrix

Thing (listening device)

Tropospheric scatter

[edit]References

1. ̂  Pozar, David M. (1993). Microwave Engineering Addison–Wesley Publishing Company. ISBN 0-201-

50418-9.

2. ̂  http://www.google.com/search?

hl=en&defl=en&q=define:microwave&ei=e6CMSsWUI5OHmQee2si1DQ&sa=X&oi=glossary_definition

&ct=title

3. ̂  Microwave Oscillator notes by Herley General Microwave

4. ̂  Liou, Kuo-Nan (2002). An introduction to atmospheric radiation. Academic Press. p. 2. ISBN 0-12-

451451-0. Retrieved 12 July 2010.

5. ̂  "IEEE 802.20: Mobile Broadband Wireless Access (MBWA)". Official web site. Retrieved August 20,

2011.

6. ̂  "the way to new energy". ITER. 2011-11-04. Retrieved 2011-11-08.

7. ̂  "Electron Cyclotron Resonance Heating (ECRH)". Ipp.mpg.de. Retrieved 2011-11-08.

8. ̂  Raytheon's Silent Guardian millimeter wave weapon[dead link]

9. ̂  "eEngineer – Radio Frequency Band Designations". Radioing.com. Retrieved 2011-11-08.

10. ̂  PC Mojo – Webs with MOJO from Cave Creek, AZ (2008-04-25). "Frequency Letter bands –

Microwave Encyclopedia". Microwaves101.com. Retrieved 2011-11-08.

11. ̂  Merrill I. Skolnik, Introduction to Radar Systems,Third Ed., Page 522, McGraw Hill, 2001,

12. ̂  Goldsmith, JR (December 1997). "Epidemiologic evidence relevant to radar (microwave)

effects". Environmental Health Perspectives 105 (Suppl. 6): 1579–

1587.DOI:10.2307/3433674. JSTOR 3433674. PMC 1469943. PMID 9467086.

13. ̂  Philip L. Stocklin, US Patent 4,858,612, December 19, 1983

14. ̂  "''The work of Jagdish Chandra Bose: 100years of MM-wave research'', retrieved 2010 01 31".

Tuc.nrao.edu. Retrieved 2011-11-08.

15. ̂  "Jazz-Funk-Groove for everyone... – Hungarian Inventors/Inventions". Dieselpingwin.multiply.com.

1928-09-09. Retrieved 2011-11-08.

Radio spectrumFrom Wikipedia, the free encyclopedia

ITU Radio Band Numbers

1 2 3 4 5 6 7 8 9 10 11 12

ITU Radio Band Symbols

ELF SLF ULF VLF LF MF HF VHF UHF SHF EHF THF

NATO Radio bands

A B C D E F G H I J K L M

IEEE Radar bands

HF VHF UHF L S C X Ku K Ka Q V W D

v d e

Radio spectrum refers to the part of the electromagnetic spectrum corresponding to radio frequencies – that

is, frequencies lower than around 300 GHz (or, equivalently, wavelengths longer than about 1 mm).

Different parts of the radio spectrum are used for different radio transmission technologies and applications.

Radio spectrum is typically government regulated in developed countries and, in some cases, is sold or

licensed to operators of private radio transmission systems (for example, cellular telephone operators or

broadcast television stations). Ranges of allocated frequencies are often referred to by their provisioned use

(for example, cellular spectrum or television spectrum).[1]

Contents

  [hide] 

1 By frequency

o 1.1 ITU

o 1.2 IEEE US

o 1.3 EU, NATO, US ECM frequency designations

o 1.4 Waveguide frequency bands

2 By application

o 2.1 Broadcasting

o 2.2 Air band

o 2.3 Marine band

o 2.4 Amateur radio frequencies

o 2.5 Citizens' band and personal radio services

o 2.6 Industrial, scientific, medical

o 2.7 Land mobile bands

o 2.8 Radio control

o 2.9 Radar

3 See also

4 References

5 External links

[edit]By frequency

A band is a small section of the spectrum of radio communication frequencies, in which channels are usually

used or set aside for the same purpose.

Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the

atmosphere is effectively opaque, until it becomes transparent again in thenear-infrared and optical window

frequency ranges.

To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated in

bands. For example, broadcasting, mobile radio, or navigation devices, will be allocated in non-overlapping

ranges of frequencies.

Each of these bands has a basic bandplan which dictates how it is to be used and shared, to

avoid interference and to set protocol for the compatibility of transmitters andreceivers.

As a matter of convention, bands are divided at wavelengths of 10n metres, or frequencies of 3×10n hertz. For

example, 30 MHz or 10 m divides shortwave (lower and longer) from VHF (shorter and higher). These are the

parts of the radio spectrum, and not its frequency allocation.

Band name AbbrITU band

Frequencyand

wavelength in airExample uses

Tremendously low frequency

TLF 0< 3 Hz

> 100,000 kmNatural and man-made electromagnetic noise

Extremely low frequency ELF 13–30 Hz

100,000 km – 10,000 kmCommunication with submarines

Super low frequency SLF 230–300 Hz

10,000 km – 1000 kmCommunication with submarines

Ultra low frequency ULF 3300–3000 Hz

1000 km – 100 kmSubmarine communication, Communication

within mines

Very low frequency VLF 43–30 kHz

100 km – 10 km

Navigation, time signals, submarine communication, wireless heart rate

monitors, geophysics

Low frequency LF 530–300 kHz

10 km – 1 km

Navigation, time signals, AM longwave broadcasting (Europe and parts

of Asia), RFID, amateur radio

Medium frequency MF 6300–3000 kHz1 km – 100 m

AM (medium-wave) broadcasts, amateur radio, avalanche beacons

High frequency HF 73–30 MHz

100 m – 10 m

Shortwave broadcasts, citizens' band radio, amateur radio and over-the-horizon aviation communications, RFID, Over-the-horizon

radar, Automatic link establishment (ALE) / Near Vertical Incidence

Skywave (NVIS) radio communications, Marine and mobile radio

telephony

Very high frequency VHF 830–300 MHz10 m – 1 m

FM, television broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft

communications. Land Mobile and Maritime Mobile communications, amateur

radio, weather radio

Ultra high frequency UHF 9300–3000 MHz1 m – 100 mm

Television broadcasts, microwave ovens, microwave devices/communications, radio

astronomy, mobile phones,wireless LAN, Bluetooth, ZigBee, GPS and two-way

radios such as Land Mobile, FRS and GMRS radios, amateur radio

Super high frequency SHF 103–30 GHz

100 mm – 10 mm

radio astronomy, microwave devices/communications, wireless LAN, most

modern radars, communications satellites, satellite television broadcasting, DBS, amateur

radio

Extremely high frequency EHF 1130–300 GHz

10 mm – 1 mm

radio astronomy, high-frequency microwave radio relay, microwave remote sensing,

amateur radio, directed-energy weapon, millimeter wave scanner

Terahertz orTremendously high frequency

THz or

THF12

300–3,000 GHz1 mm – 100 μm

Terahertz imaging – a potential replacement for X-rays in some medical applications,

ultrafast molecular dynamics,condensed-matter physics, terahertz time-domain spectroscopy,

terahertz computing/communications, sub-mm remote sensing, amateur radio

[edit]ITU

The ITU radio bands are designations defined in the ITU Radio Regulations. Article 2, provision No. 2.1 states

that "the radio spectrum shall be subdivided into nine frequency bands, which shall be designated by

progressive whole numbers in accordance with the following table[2]".

The table originated with a recommendation of the IVth CCIR meeting, held in Bucharest in 1937, and was

approved by the International Radio Conference held at Atlantic City in 1947. The idea to give each band a

number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band

limits in Hz, originated with B.C. Fleming-Williams, who suggested it in a letter to the editor of Wireless

Engineer in 1942. (For example, the approximate geometric mean of Band 7 is 10 MHz, or 107 Hz.)[3]

Table of ITU Radio Bands

Band Number

SymbolsFrequency

RangeWavelength Range†

4 VLF 3 to 30 kHz 10 to 100 km

5 LF 30 to 300 kHz 1 to 10 km

6 MF 300 to 3000 kHz 100 to 1000 m

7 HF 3 to 30 MHz 10 to 100 m

8 VHF 30 to 300 MHz 1 to 10 m

9 UHF 300 to 3000 MHz 10 to 100 cm

10 SHF 3 to 30 GHz 1 to 10 cm

11 EHF 30 to 300 GHz 1 to 10 mm

12 THF 300 to 3000  GHz 0.1 to 1 mm

† This column does not form part of the table in Provision No. 2.1 of the Radio Regulations

[edit]IEEE US

Table of IEEE bands[4]

BandFrequency

rangeOrigin of name

[citation needed]

HF band 3 to 30 MHz High Frequency

[edit]EU, NATO, US ECM frequency designations

Band Frequency range

A band 0 to 0.25 GHz

[edit]Waveguide frequency bands

BandFrequency

range [5]

R band1.70 to 2.60 GHz

VHF band

30 to 300 MHz Very High Frequency

UHF band

300 to 1000 MHz Ultra High Frequency

L band 1 to 2 GHz Long wave

S band 2 to 4 GHz Short wave

C band 4 to 8 GHzCompromise between S and X

X band 8 to 12 GHzUsed in WW II for fire control, X for cross (as incrosshair)

Ku band 12 to 18 GHz Kurz-under

K band 18 to 27 GHz German Kurz (short)

Ka band 27 to 40 GHz Kurz-above

V band 40 to 75 GHz

W band 75 to 110 GHz W follows V in thealphabet

mm   band 110 to 300 GHz

B band 0.25 to 0.5 GHz

C band 0.5 to 1.0 GHz

D band 1 to 2 GHz

E band 2 to 3 GHz

F band 3 to 4 GHz

G band 4 to 6 GHz

H band 6 to 8 GHz

I band 8 to 10 GHz

J band 10 to 20 GHz

K band 20 to 40 GHz

L band 40 to 60 GHz

M band

60 to 100 GHz

D band

2.20 to 3.30 GHz

S band2.60 to 3.95 GHz

E band3.30 to 4.90 GHz

G band

3.95 to 5.85 GHz

F band4.90 to 7.05 GHz

C band5.85 to 8.20 GHz

H band

7.05 to 10.10 GHz

X band

8.2 to 12.4 GHz

Ku band

12.4 to 18.0 GHz

K band

15.0 to 26.5 GHz

Ka band

26.5 to 40.0 GHz

Q band

33 to 50 GHz

U band

40 to 60 GHz

V band

50 to 75 GHz

W band

75 to 110 GHz

Y band

325 to 500 GHz

[edit]By application

[edit]Broadcasting

Broadcast frequencies:

Longwave AM Radio  = 148.5 – 283.5 kHz (LF)

Mediumwave AM Radio  = 530 kHz – 1710 kHz (MF)

Shortwave AM Radio  = 3 MHz – 30 MHz (HF)

Designations for television and FM radio broadcast frequencies vary between countries, see Television channel

frequencies and FM broadcast band. Since VHF and UHF frequencies are desirable for many uses in urban

areas, in North America some parts of the former television broadcasting band have been reassigned

to cellular phone and various land mobile communications systems. Even within the allocation still dedicated to

television, TV-band devices use channels without local broadcasters.

The Apex band in the United States was a pre-WWII allocation for VHF audio broadcasting; it was made

obsolete after the introduction of FM broadcasting.

[edit]Air band

Airband refers to VHF frequencies used for navigation and voice communication with aircraft. Trans-oceanic

aircraft also carry HF radio and satellite transceivers.

[edit]Marine band

The greatest incentive for development of radio was the need to communicate with ships out of visual range of

shore. From the very early days of radio, large oceangoing vessels carried powerful long-wave and medium-

wave transmitters. High-frequency allocations are still designated for ships, although satellite systems have

taken over some of the safety applications previously served by 500 kHz and other frequencies. 2182 kHz is a

medium-wave frequency still used for marine emergency communication.

Marine VHF radio is used in coastal waters and relatively short-range communication between vessels and to

shore stations. Radios are channelized, with different channels used for different purposes; marine Channel 16

is used for calling and emergencies.

[edit]Amateur radio frequencies

Amateur radio frequency allocations vary around the world. Several bands are common for amateurs world-

wide, usually in the shortwave part of the spectrum. Other bands are national or regional allocations only due to

differing allocations for other services, especially in the VHF and UHF parts of the radio spectrum.

[edit]Citizens' band and personal radio services

Citizens' band radio is allocated in many countries, using channelized radios in the upper HF part of the

spectrum (around 27 MHz). It used for personal, small business and hobby purposes. Other frequency

allocations are used for similar services in different jurisdictions, for example UHF CB is allocated in Australia.

A wide range of personal radio servicesexist around the world, usually emphasizing short-range communication

between individuals or for small businesses, simplified or no license requirements, and usually FM transceivers

using around 1 watt or less.

[edit]Industrial, scientific, medical

The ISM bands were initially reserved for non-communications uses of RF energy, such as microwave ovens,

radio-frequency heating, and similar purposes. However in recent years the largest use of these bands has

been by short-range low-power communications systems, since users do not have to hold a radio operator's

license. Cordless telephones,wireless computer networks, Bluetooth devices, and garage door openers all use

the ISM bands. ISM devices do not have regulatory protection against interference from other users of the

band.

[edit]Land mobile bands

Bands of frequencies, especially in the VHF and UHF parts of the spectrum, are allocated for communication

between fixed base stations and land mobile vehicle-mounted orportable transceivers. In the United States

these services are informally known as business band radio. See also Professional mobile radio.

Police radio and other public safety services such as fire departments and ambulances are generally found in

the VHF and UHF parts of the spectrum. Trunking systems are often used to make most efficient use of the

limited number of frequencies available.

The demand for mobile telephone service has led to large blocks of radio spectrum allocated to cellular

frequencies.

[edit]Radio control

Reliable radio control uses bands dedicated to the purpose. Radio-controlled toys may use portions of

unlicensed spectrum in the 27 MHz or 49 MHz bands, but more costly aircraft, boat, or land vehicle models use

dedicated remote control frequencies near 72 MHz to avoid interference by unlicensed uses. Licensed amateur

radio operators use portions of the 6-meter band in North America. Industrial remote control of cranes or

railway locomotives use assigned frequencies that vary by area.

[edit]Radar

Radar applications use relatively high power pulse transmitters and sensitive receivers, so radar is operated on

bands not used for other purposes. Most radar bands are in themicrowave part of the spectrum, although

certain important applications for meteorology make use of powerful transmitters in the UHF band.

[edit]See also

Bandplan

DXing

Frequency allocation

Geneva Frequency Plan of 1975

North American Radio Broadcasting Agreement

Open spectrum

Radio astronomy

Radio communication system

Scanner (radio)

Two-way radio

Ultra-wideband

U-NII

WARC bands

[edit]References

1. ̂  Colin Robinson (2003). Competition and regulation in utility markets. Edward Elgar Publishing.

p. 175. ISBN 978-1-84376-230-0.

2. ̂  ITU Radio Regulations, Volume 1, Article 2; Edition of 2008. Available online at [1]

3. ̂  Booth, C.F. (1949). "Nomenclature of Frequencies". The Post Office Electrical Engineers' Journal 42 (1):

47–48.

4. ̂  Per IEEE Std 521-2002 Standard Letter Designations for Radar-Frequency Bands. Reaffirmed standard

of 1984; originally dates back to World War II.

5. ̂  www.microwaves101.com "Waveguide frequency bands and interior dimensions"

ITU-R Recommendation V.431: Nomenclature of the frequency and wavelength bands used in

telecommunications. International Telecommunication Union, Geneva.

IEEE Standard 521-2002: Standard Letter Designations for Radar-Frequency Bands

AFR 55-44/AR 105-86/OPNAVINST 3430.9A/MCO 3430.1, 27 October 1964 superseded by AFR

55-44/AR 105-86/OPNAVINST 3430.1A/MCO 3430.1A, 6 December 1978: Performing Electronic

Countermeasures in the United States and Canada, Attachment 1,ECM Frequency Authorizations.