Microwave
One set of microwave frequency bands designations by the Radio Society of Great Britain (RSGB), is tabulated below: Other definitions exist.Microwaves are absorbed by moisture in the atmosphere, and the attenuation increases with frequency, becoming a significant factor (rain fade) at the high end of the band.As a consequence, practical microwave circuits tend to move away from the discrete resistors, capacitors, and inductors used with lower-frequency radio waves.[14] In turn, at even higher frequencies, where the wavelength of the electromagnetic waves becomes small in comparison to the size of the structures used to process them, microwave techniques become inadequate, and the methods of optics are used.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.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 and 11 GHz.Microwave radar is widely used for applications such as air traffic control, weather forecasting, navigation of ships, and speed limit enforcement.The world's largest ground-based astronomy project to date, it consists of more than 66 dishes and was built in an international collaboration by Europe, North America, East Asia and Chile.Microwave ovens became common kitchen appliances in Western countries in the late 1970s, following the development of less expensive cavity magnetrons.Many semiconductor processing techniques use microwaves to generate plasma for such purposes as reactive ion etching and plasma-enhanced chemical vapor deposition (PECVD).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.They concentrated on producing short wavelength radio waves in the UHF and microwave ranges, with which they could duplicate classic optics experiments in their laboratories, using quasioptical components such as prisms and lenses made of paraffin, sulfur and pitch and wire diffraction gratings, to refract and diffract radio waves like light rays.[31] Hertz produced waves up to 450 MHz; his directional 450 MHz transmitter consisted of a 26 cm brass rod dipole antenna with a spark gap between the ends, suspended at the focal line of a parabolic antenna made of a curved zinc sheet, powered by high voltage pulses from an induction coil.Independently in 1894, Oliver Lodge and Augusto Righi experimented with 1.5 and 12 GHz microwaves respectively, generated by small metal ball spark resonators.In 1931 an Anglo-French consortium headed by Andre C. Clavier demonstrated the first experimental microwave relay link, across the English Channel 40 miles (64 km) between Dover, UK and Calais, France.[38][39] The system transmitted telephony, telegraph and facsimile data over bidirectional 1.7 GHz beams with a power of one-half watt, produced by miniature Barkhausen–Kurz tubes at the focus of 10-foot (3 m) metal dishes.[39][40] The development of radar, mainly in secrecy, before and during World War II, resulted in the technological advances which made microwaves practical.It was found that conventional transmission lines used to carry radio waves had excessive power losses at microwave frequencies, and George Southworth at Bell Labs and Wilmer Barrow at MIT independently invented waveguide in 1936.[30] Ten centimeter (3 GHz) microwave radar powered by the magnetron tube was in use on British warplanes in late 1941 and proved to be a game changer.The MIT Radiation Laboratory established secretly at Massachusetts Institute of Technology in 1940 to research radar, produced much of the theoretical knowledge necessary to use microwaves.The first microwave relay systems were developed by the Allied military near the end of the war and used for secure battlefield communication networks in the European theater.[30] Due to their high frequency they had a very large information-carrying capacity (bandwidth); a single microwave beam could carry tens of thousands of phone calls.In the 1950s and 60s transcontinental microwave relay networks were built in the US and Europe to exchange telephone calls between cities and distribute television programs.The first communications satellites were launched in the 1960s, which relayed telephone calls and television between widely separated points on Earth using microwave beams.In 1964, Arno Penzias and Robert Woodrow Wilson while investigating noise in a satellite horn antenna at Bell Labs, Holmdel, New Jersey discovered cosmic microwave background radiation.Microwave radar became the central technology used in air traffic control, maritime navigation, anti-aircraft defense, ballistic missile detection, and later many other uses.[42] In 1945 Percy Spencer, an engineer working on radar at Raytheon, noticed that microwave radiation from a magnetron oscillator melted a candy bar in his pocket.Negative resistance amplifier circuits required the invention of new nonreciprocal waveguide components, such as circulators, isolators, and directional couplers.In 1969 Kaneyuki Kurokawa derived mathematical conditions for stability in negative resistance circuits which formed the basis of microwave oscillator design.Today MMICs have become the workhorses of both analog and digital high-frequency electronics, enabling the production of single-chip microwave receivers, broadband amplifiers, modems, and microprocessors.
Microwave ovenMicrowaves (disambiguation)microwave relayFrazier PeakCaliforniaradomeselectromagnetic radiationwavelengthsradio wavesinfraredfrequenciesradio-frequency engineeringprefixmicrometerradio technologyfar infraredterahertz radiationultra-high-frequencysuper high frequency (SHF)extremely high frequencymillimeter waveKa bandline-of-sightground wavesionospherepoint-to-pointwireless networksmicrowave radio relaysatellite and spacecraft communicationdiathermyremote sensingradio astronomyparticle acceleratorsspectroscopycollision avoidance systemsgarage door openerskeyless entry systemsmicrowave ovenselectromagnetic spectrumPhotonenergyGamma rayUltravioletVisible lightRadio Society of Great BritainRadio bands1 (ELF)2 (SLF)3 (ULF)4 (VLF)5 (LF)6 (MF)7 (HF)8 (VHF)9 (UHF)10 (SHF)11 (EHF)12 (THF)EU / NATO / US ECM L bandS bandC bandX bandKu bandK bandQ bandU bandV bandW bandF bandD bandRadio propagationattenuationskywavesFresnel zonerain fadeopaqueoptical windowTropospheric scattertropospherewaveguidesdiplexerair traffic controlomnidirectional antennaswireless devicescell phonescordless phoneswireless LANslaptopsBluetoothwhip antennasrubber ducky antennasdipolespatch antennasinverted F antennawavelengthhigh gainantennasfrequency reuseParabolic ("dish") antennashorn antennasslot antennaslens antennasmicrostrip antennasphased arraytransmission linescoaxial cableparallel wire linestransmitterRF front endreceiverelectromagneticscircuit theorylumped-element circuit theorydistributed circuit elementsresistorscapacitorsinductorsstriplineresonatorsresonant stubsopticscavity magnetronmicrostripradar speed gunhorn antenna