A report on Microwave

A telecommunications tower with a variety of dish antennas for microwave relay links on Frazier Peak, Ventura County, California. The apertures of the dishes are covered by plastic sheets (radomes) to keep out moisture.
The atmospheric attenuation of microwaves and far infrared radiation 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. This graph includes a range of frequencies from 0 to 1 THz; the microwaves are the subset in the range between 0.3 and 300 gigahertz.
Waveguide is used to carry microwaves. Example of waveguides and a diplexer in an air traffic control radar
Disassembled radar speed gun. The grey assembly attached to the end of the copper-colored horn antenna is the Gunn diode which generates the microwaves.
A satellite dish on a residence, which receives satellite television over a Ku band 12–14 GHz microwave beam from a direct broadcast communications satellite in a geostationary orbit 35,700 kilometres (22,000 miles) above the Earth
The parabolic antenna (lower curved surface) of an ASR-9 airport surveillance radar which radiates a narrow vertical fan-shaped beam of 2.7–2.9 GHz (S band) microwaves to locate aircraft in the airspace surrounding an airport.
Small microwave oven on a kitchen counter
Microwaves are widely used for heating in industrial processes. A microwave tunnel oven for softening plastic rods prior to extrusion.
Absorption wavemeter for measuring in the Ku band.
1.2 GHz microwave spark transmitter (left) and coherer receiver (right) used by Guglielmo Marconi during his 1895 experiments had a range of 6.5 km
ku band microstrip circuit used in satellite television dish.
Heinrich Hertz's 450 MHz spark transmitter, 1888, consisting of 23 cm dipole and spark gap at focus of parabolic reflector
Jagadish Chandra Bose in 1894 was the first person to produce millimeter waves; his spark oscillator (in box, right) generated 60 GHz (5 mm) waves using 3 mm metal ball resonators.
Microwave spectroscopy experiment by John Ambrose Fleming in 1897 showing refraction of 1.4 GHz microwaves by paraffin prism, duplicating earlier experiments by Bose and Righi.
Augusto Righi's 12 GHz spark oscillator and receiver, 1895
Antennas of 1931 experimental 1.7 GHz microwave relay link across the English Channel.
Experimental 700 MHz transmitter 1932 at Westinghouse labs transmits voice over a mile.
Southworth (at left) demonstrating waveguide at IRE meeting in 1938, showing 1.5 GHz microwaves passing through the 7.5 m flexible metal hose registering on a diode detector.
The first modern horn antenna in 1938 with inventor Wilmer L. Barrow
thumb|Randall and Boot's prototype cavity magnetron tube at the University of Birmingham, 1940. In use the tube was installed between the poles of an electromagnet
First commercial klystron tube, by General Electric, 1940, sectioned to show internal construction
British Mk. VIII, the first microwave air intercept radar, in nose of British fighter. Microwave radar, powered by the new magnetron tube, significantly shortened World War II.
Mobile US Army microwave relay station 1945 demonstrating relay systems using frequencies from 100 MHz to 4.9 GHz which could transmit up to 8 phone calls on a beam.

Form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively.

- Microwave
A telecommunications tower with a variety of dish antennas for microwave relay links on Frazier Peak, Ventura County, California. The apertures of the dishes are covered by plastic sheets (radomes) to keep out moisture.

117 related topics with Alpha

Overall

Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (−). Loops of electric field leave the antenna and travel away at the speed of light; these are the radio waves. In this animation the action is shown slowed down enormously.

Radio wave

18 links

Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below.

Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below.

Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (−). Loops of electric field leave the antenna and travel away at the speed of light; these are the radio waves. In this animation the action is shown slowed down enormously.
Diagram of the electric fields (E) and magnetic fields (H) of radio waves emitted by a monopole radio transmitting antenna (small dark vertical line in the center). The E and H fields are perpendicular, as implied by the phase diagram in the lower right.
Animated diagram of a half-wave dipole antenna receiving a radio wave. The antenna consists of two metal rods connected to a receiver R. The electric field ( E, green arrows ) of the incoming wave pushes the electrons in the rods back and forth, charging the ends alternately positive (+) and negative (−) . Since the length of the antenna is one half the wavelength of the wave, the oscillating field induces standing waves of voltage ( V, represented by red band ) and current in the rods. The oscillating currents (black arrows) flow down the transmission line and through the receiver (represented by the resistance R).

All warm objects radiate high frequency radio waves (microwaves) as part of their black body radiation.

A stack of "fishbone" and Yagi–Uda television antennas

Antenna (radio)

15 links

Antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.

Antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.

A stack of "fishbone" and Yagi–Uda television antennas
Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (−). Loops of electric field leave the antenna and travel away at the speed of light; these are the radio waves. In this animation the action is shown slowed down enormously.
Electronic symbol for an antenna
Antennas of the Atacama Large Millimeter/submillimeter Array.
An automobile's whip antenna, a common example of an omnidirectional antenna.
Half-wave dipole antenna
Diagram of the electric fields ( blue ) and magnetic fields ( red ) radiated by a dipole antenna ( black rods) during transmission.
Cell phone base station antennas
Standing waves on a half wave dipole driven at its resonant frequency. The waves are shown graphically by bars of color ( red for voltage, V and blue for current, I ) whose width is proportional to the amplitude of the quantity at that point on the antenna.
Typical center-loaded mobile CB antenna with loading coil
Polar plots of the horizontal cross sections of a (virtual) Yagi-Uda-antenna. Outline connects points with 3 dB field power compared to an ISO emitter.
The wave reflected by earth can be considered as emitted by the image antenna.
The currents in an antenna appear as an image in opposite phase when reflected at grazing angles. This causes a phase reversal for waves emitted by a horizontally polarized antenna (center) but not for a vertically polarized antenna (left).
frame

A receiving antenna may include not only the passive metal receiving elements, but also an integrated preamplifier or mixer, especially at and above microwave frequencies.

A portable battery-powered AM/FM broadcast receiver, used to listen to audio broadcast by local radio stations.

Radio receiver

15 links

Electronic device that receives radio waves and converts the information carried by them to a usable form.

Electronic device that receives radio waves and converts the information carried by them to a usable form.

A portable battery-powered AM/FM broadcast receiver, used to listen to audio broadcast by local radio stations.
A modern communications receiver, used in two-way radio communication stations to talk with remote locations by shortwave radio.
Girl listening to vacuum tube radio in the 1940s. During the golden age of radio, 1925–1955, families gathered to listen to the home radio receiver in the evening
A bedside clock radio that combines a radio receiver with an alarm clock
Symbol for an antenna
Symbol for a bandpass filter used in block diagrams of radio receivers
Symbol for an amplifier
Symbol for a demodulator
Envelope detector circuit
How an envelope detector works
Block diagram of a tuned radio frequency receiver. To achieve enough selectivity to reject stations on adjacent frequencies, multiple cascaded bandpass filter stages had to be used. The dotted line indicates that the bandpass filters must be tuned together.
Block diagram of a superheterodyne receiver. The dotted line indicates that the RF filter and local oscillator must be tuned in tandem.
Block diagram of a dual-conversion superheterodyne receiver
Guglielmo Marconi, who built the first radio receivers, with his early spark transmitter (right) and coherer receiver (left) from the 1890s. The receiver records the Morse code on paper tape
Generic block diagram of an unamplified radio receiver from the wireless telegraphy era
Example of transatlantic radiotelegraph message recorded on paper tape by a siphon recorder at RCA's New York receiving center in 1920. The translation of the Morse code is given below the tape.
Coherer from 1904 as developed by Marconi.
Experiment to use human brain as a radio wave detector, 1902
Magnetic detector
Electrolytic detector
A galena cat's whisker detector from a 1920s crystal radio
Marconi's inductively coupled coherer receiver from his controversial April 1900 "four circuit" patent no. 7,777.
Radio receiver with Poulsen "tikker" consisting of a commutator disk turned by a motor to interrupt the carrier.
Fessenden's heterodyne radio receiver circuit
Unlike today, when almost all radios use a variation of the superheterodyne design, during the 1920s vacuum tube radios used a variety of competing circuits.
During the "Golden Age of Radio" (1920 to 1950), families gathered to listen to the home radio in the evening, such as this Zenith console model 12-S-568 from 1938, a 12-tube superheterodyne with pushbutton tuning and 12-inch cone speaker.
De Forest's first commercial Audion receiver, the RJ6 which came out in 1914. The Audion tube was always mounted upside down, with its delicate filament loop hanging down, so it did not sag and touch the other electrodes in the tube.
Block diagram of regenerative receiver
Circuit of single tube Armstrong regenerative receiver
Armstrong presenting his superregenerative receiver, June 28, 1922, Columbia University
Hazeltine's prototype Neutrodyne receiver, presented at a March 2, 1923 meeting of the Radio Society of America at Columbia University.
Block diagram of simple single tube reflex receiver
The first superheterodyne receiver built at Armstrong's Signal Corps laboratory in Paris during World War I. It is constructed in two sections, the mixer and local oscillator (left) and three IF amplification stages and a detector stage (right). The intermediate frequency was 75 kHz.
A Zenith transistor based portable radio receiver
A modern smartphone has several RF CMOS digital radio transmitters and receivers to connect to different devices, including a cellular receiver, wireless modem, Bluetooth modem, and GPS receiver.

Satellite TV receiver - a set-top box which receives subscription direct-broadcast satellite television, and displays it on an ordinary television. A rooftop satellite dish receives many channels all modulated on a Ku band microwave downlink signal from a geostationary direct broadcast satellite 22,000 mi above the Earth, and the signal is converted to a lower intermediate frequency and transported to the box through a coaxial cable. The subscriber pays a monthly fee.

400x400px

Electromagnetic radiation

10 links

In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, propagating through space, carrying electromagnetic radiant energy.

In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, propagating through space, carrying electromagnetic radiant energy.

400x400px
Shows the relative wavelengths of the electromagnetic waves of three different colours of light (blue, green, and red) with a distance scale in micrometers along the x-axis.
In electromagnetic radiation (such as microwaves from an antenna, shown here) the term "radiation" applies only to the parts of the electromagnetic field that radiate into infinite space and decrease in intensity by an inverse-square law of power, so that the total radiation energy that crosses through an imaginary spherical surface is the same, no matter how far away from the antenna the spherical surface is drawn. Electromagnetic radiation thus includes the far field part of the electromagnetic field around a transmitter. A part of the "near-field" close to the transmitter, forms part of the changing electromagnetic field, but does not count as electromagnetic radiation.
Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D animation shows a plane linearly polarized wave propagating from left to right. The electric and magnetic fields in such a wave are in-phase with each other, reaching minima and maxima together.
Representation of the electric field vector of a wave of circularly polarized electromagnetic radiation.
James Clerk Maxwell
Electromagnetic spectrum with visible light highlighted
Rough plot of Earth's atmospheric absorption and scattering (or opacity) of various wavelengths of electromagnetic radiation

It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.

A U.S. Space Force Extremely High Frequency communications satellite relays secure communications for the United States and other allied countries.

Communications satellite

11 links

Artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth.

Artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth.

A U.S. Space Force Extremely High Frequency communications satellite relays secure communications for the United States and other allied countries.
Replica of Sputnik 1
The Atlas-B with SCORE on the launch pad; the rocket (without booster engines) constituted the satellite.
Geostationary orbit
An Iridium satellite

Communications satellites use a wide range of radio and microwave frequencies.

A variety of radio antennas on Sandia Peak near Albuquerque, New Mexico, US

Radio

13 links

Technology of signaling and communicating using radio waves.

Technology of signaling and communicating using radio waves.

A variety of radio antennas on Sandia Peak near Albuquerque, New Mexico, US
Radio communication. Information such as sound is converted by a transducer such as a microphone to an electrical signal, which modulates a radio wave produced by the transmitter. A receiver intercepts the radio wave and extracts the information-bearing modulation signal, which is converted back to a human usable form with another transducer such as a loudspeaker.
Comparison of AM and FM modulated radio waves
Frequency spectrum of a typical modulated AM or FM radio signal. It consists of a component C at the carrier wave frequency f_c with the information (modulation) contained in two narrow bands of frequencies called sidebands (SB) just above and below the carrier frequency.
Satellite television dish on a residence
Satellite phones, showing the large antennas needed to communicate with the satellite
Firefighter using walkie-talkie
VHF marine radio on a ship
Parabolic antennas of microwave relay links on tower in Australia
RFID tag from a DVD
Satellite Communications Center Dubna in Russia
Communications satellite belonging to Azerbaijan
Military air traffic controller on US Navy aircraft carrier monitors aircraft on radar screen
ASR-8 airport surveillance radar antenna. It rotates once every 4.8 seconds. The rectangular antenna on top is the secondary radar.
Rotating marine radar antenna on a ship
A personal navigation assistant GPS receiver in a car, which can give driving directions to a destination.
EPIRB emergency locator beacon on a ship
Wildlife officer tracking radio-tagged mountain lion
US Air Force MQ-1 Predator drone flown remotely by a pilot on the ground
Remote keyless entry fob for a car
Quadcopter, a popular remote-controlled toy
Television receiver

Satellite radio is a subscription radio service that broadcasts CD quality digital audio direct to subscribers' receivers using a microwave downlink signal from a direct broadcast communication satellite in geostationary orbit 22,000 miles above the Earth. It is mostly intended for car radios in vehicles. Satellite radio uses the 2.3 GHz S band in North America, in other parts of the world, it uses the 1.4 GHz L band allocated for DAB.

301x301px

Microwave oven

10 links

301x301px
The cavity magnetron developed by John Randall and Harry Boot in 1940 at the University of Birmingham, England
Microwave ovens, several from the 1980s
Raytheon RadaRange aboard the NS Savannah nuclear-powered cargo ship, installed circa 1961
1974 Radarange RR-4.
By the late 1970s, technological advances led to rapidly falling prices. Often called "electronic ovens" in the 1960s, the name "microwave oven" later gained currency, and they are now informally called "microwaves".
A microwave oven, c. 2005
A magnetron with section removed (magnet is not shown)
Inner space of an microwave oven and control panels.
In addition to their use in heating food, microwave ovens are widely used for heating in industrial processes. A microwave tunnel oven for softening plastic rods prior to extrusion.
Charred popcorn burnt by leaving the microwave oven on too long
A microwave oven with a metal shelf
A microwaved DVD-R disc showing the effects of electrical discharge through its metal film
Microwave-safe symbol

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.

Later thermionic vacuum tubes, mostly miniature style, some with top cap connections for higher voltages

Vacuum tube

11 links

Device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.

Device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.

Later thermionic vacuum tubes, mostly miniature style, some with top cap connections for higher voltages
Audio power amplifier using tubes, in operation. Red-orange glow is from heated filaments.
Illustration representing a primitive triode vacuum tube and the polarities of the typical dc operating potentials. Not shown are the impedances (resistors or inductors) that would be included in series with the C and B voltage sources.
Radio station signal generator with vacuum tubes
One of Edison's experimental bulbs
Fleming's first diodes
The first triode, the de Forest Audion, invented in 1906
Triodes as they evolved over 40 years of tube manufacture, from the RE16 in 1918 to a 1960s era miniature tube
Triode symbol. From top to bottom: plate (anode), control grid, cathode, heater (filament)
General Electric Company Pliotron, Science History Institute
Tetrode symbol. From top to bottom: plate (anode), screen grid, control grid, cathode, heater (filament).
The useful region of operation of the screen grid tube (tetrode) as an amplifier is limited to anode potentials in the straight portions of the characteristic curves greater than the screen grid potential.
The pentagrid converter contains five grids between the cathode and the plate (anode)
Beam power tube designed for radio frequency use
Miniature tube (right) compared to the older octal style. Not including pins, the larger tube, a 5U4GB, is 93 mm high with a 35 mm diameter base, while the smaller, a 9-pin 12AX7, is 45 mm high, and 20.4 mm in diameter.
Subminiature CV4501 tube (SQ version of EF72), 35 mm long x 10 mm diameter (excluding leads)
RCA 6DS4 "Nuvistor" triode, c. 20 mm high by 11 mm diameter
Commercial packaging for vacuum tubes used in the latter half of the 20th century including boxes for individual tubes (bottom right), sleeves for rows of the boxes (left), and bags that smaller tubes would be put in by a store upon purchase (top right)
The 1946 ENIAC computer used 17,468 vacuum tubes and consumed 150 kW of power
Vacuum tubes seen on end in a recreation of the World War II-era Colossus computer at Bletchley Park, England
Circuitry from core memory unit of Whirlwind
The anode (plate) of this transmitting triode has been designed to dissipate up to 500 W of heat
Metal-cased tubes with octal bases
Triode tube type GS-9B; designed for use at radio frequencies up to 2000 MHz and rated for 300 watts anode power dissipation. The finned heat sink provides conduction of heat from anode to air stream.
Voltage-regulator tube in operation. Low-pressure gas within tube glows due to current flow.
Batteries for a vacuum-tube circuit. The C battery is highlighted.
Tube tester manufactured in 1930.
Getter in opened tube; silvery deposit from getter
Dead vacuum fluorescent display (air has leaked in and the getter spot has become white)
Universal vacuum tube tester
70-watt tube-hybrid audio amplifier
Typical Triode Plate Characteristics

by frequency range (audio, radio, VHF, UHF, microwave)

Magnetron with section removed to exhibit the cavities. The cathode in the center is not visible. The antenna emitting microwaves is at the left. The magnets producing a field parallel to the long axis of the device are not shown.

Cavity magnetron

10 links

High-power vacuum tube used in early radar systems and currently in microwave ovens and linear particle accelerators.

High-power vacuum tube used in early radar systems and currently in microwave ovens and linear particle accelerators.

Magnetron with section removed to exhibit the cavities. The cathode in the center is not visible. The antenna emitting microwaves is at the left. The magnets producing a field parallel to the long axis of the device are not shown.
A similar magnetron with a different section removed. Central cathode is visible; antenna conducting microwaves at the top; magnets are not shown.
Obsolete 9 GHz magnetron tube and magnets from a Soviet aircraft radar. The tube is embraced between the poles of two horseshoe-shaped alnico magnets (top, bottom), which create a magnetic field along the axis of the tube. The microwaves are emitted from the waveguide aperture (top) which in use is attached to a waveguide conducting the microwaves to the radar antenna. Modern tubes use rare-earth magnets, electromagnets or ferrite magnets which are much less bulky.
Split-anode magnetron (c. 1935). (left) The bare tube, about 11 cm high. (right) Installed for use between the poles of a strong permanent magnet
A cross-sectional diagram of a resonant cavity magnetron. Magnetic lines of force are parallel to the geometric axis of this structure.
Cutaway drawing of a cavity magnetron of 1984. Part of the righthand magnet and copper anode block is cut away to show the cathode and cavities. This older magnetron uses two horseshoe shaped alnico magnets, modern tubes use rare-earth magnets.
9.375 GHz 20 kW (peak) magnetron assembly for an early commercial airport radar in 1947. In addition to the magnetron (right), it contains a TR (transmit/receive) switch tube and the superheterodyne receiver front end, a 2K25 reflex klystron tube local oscillator and a 1N21 germanium diode mixer. The waveguide aperture (left) is connected to the waveguide going to the antenna.
Magnetron from a microwave oven with magnet in its mounting box. The horizontal plates form a heat sink, cooled by airflow from a fan. The magnetic field is produced by two powerful ring magnets, the lower of which is just visible. Almost all modern oven magnetrons are of similar layout and appearance.
Sir John Randall and Harry Boot's original cavity magnetron developed in 1940 at the University of Birmingham, England
The electromagnet used in conjunction with Randall and Boot's original magnetron
The anode block which is part of the cavity magnetron developed by Randall and Boot
ISO 7010 Warning sign: Non-ionizing radiation

It generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of cavity resonators, which are small, open cavities in a metal block.

Experimental radar antenna, US Naval Research Laboratory, Anacostia, D. C., from the late 1930s (photo taken in 1945).

Radar

13 links

Detection system that uses radio waves to determine the distance (ranging), angle, and radial velocity of objects relative to the site.

Detection system that uses radio waves to determine the distance (ranging), angle, and radial velocity of objects relative to the site.

Experimental radar antenna, US Naval Research Laboratory, Anacostia, D. C., from the late 1930s (photo taken in 1945).
The first workable unit built by Robert Watson-Watt and his team
A Chain Home tower in Great Baddow, Essex, United Kingdom
Memorial plaque commemorating Robert Watson-Watt and Arnold Wilkins
Commercial marine radar antenna. The rotating antenna radiates a vertical fan-shaped beam.
3D Doppler Radar Spectrum showing a Barker Code of 13
Brightness can indicate reflectivity as in this 1960 weather radar image (of Hurricane Abby). The radar's frequency, pulse form, polarization, signal processing, and antenna determine what it can observe.
Change of wavelength caused by motion of the source.
Radar multipath echoes from a target cause ghosts to appear.
Pulse radar: The round-trip time for the radar pulse to get to the target and return is measured. The distance is proportional to this time.
Continuous wave (CW) radar. Using frequency modulation allows range to be extracted.
Pulse-Doppler signal processing. The Range Sample axis represents individual samples taken in between each transmit pulse. The Range Interval axis represents each successive transmit pulse interval during which samples are taken. The Fast Fourier Transform process converts time-domain samples into frequency domain spectra. This is sometimes called the bed of nails.
Radar components
AS-3263/SPS-49(V) antenna (US Navy)
Surveillance radar antenna
Slotted waveguide antenna
Phased array: Not all radar antennas must rotate to scan the sky.

A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver and processor to determine properties of the objects.