A stack of "fishbone" and Yagi–Uda television antennas
A portable battery-powered AM/FM broadcast receiver, used to listen to audio broadcast by local radio stations.
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.
A modern communications receiver, used in two-way radio communication stations to talk with remote locations by shortwave radio.
Electronic symbol for an antenna
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
Antennas of the Atacama Large Millimeter/submillimeter Array.
A bedside clock radio that combines a radio receiver with an alarm clock
An automobile's whip antenna, a common example of an omnidirectional antenna.
Symbol for an antenna
Half-wave dipole antenna
Symbol for a bandpass filter used in block diagrams of radio receivers
Diagram of the electric fields ( blue ) and magnetic fields ( red ) radiated by a dipole antenna ( black rods) during transmission.
Symbol for an amplifier
Cell phone base station antennas
Symbol for a demodulator
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.
Envelope detector circuit
Typical center-loaded mobile CB antenna with loading coil
How an envelope detector works
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.
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.
The wave reflected by earth can be considered as emitted by the image antenna.
Block diagram of a superheterodyne receiver. The dotted line indicates that the RF filter and local oscillator must be tuned in tandem.
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).
Block diagram of a dual-conversion superheterodyne receiver
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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.

In radio engineering, an 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 (radio)

It is used with an antenna.

- Radio receiver
A stack of "fishbone" and Yagi–Uda television antennas

11 related topics

Alpha

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

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).

Radio waves are generated artificially by an electronic device called a transmitter, which is connected to an antenna which radiates the waves.

They are received by another antenna connected to a radio receiver, which processes the received signal.

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.

Microwave

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

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

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.

Their short wavelength also allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter.

Due to the high cost and maintenance requirements of 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.

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

Radio

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

They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves, and received by another antenna connected to a radio receiver.

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

Radar

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.

Line of sight propagation to an antenna

Line-of-sight propagation

Characteristic of electromagnetic radiation or acoustic wave propagation which means waves travel in a direct path from the source to the receiver.

Characteristic of electromagnetic radiation or acoustic wave propagation which means waves travel in a direct path from the source to the receiver.

Line of sight propagation to an antenna
Objects within the Fresnel zone can disturb line of sight propagation even if they don't block the geometric line between antennas.
Two stations not in line-of-sight may be able to communicate through an intermediate radio repeater station.
R is the radius of the Earth, h is the height of the transmitter (exaggerated), d is the line of sight distance

Thus, any obstruction between the transmitting antenna (transmitter) and the receiving antenna (receiver) will block the signal, just like the light that the eye may sense.

The radio horizon is the locus of points at which direct rays from an antenna are tangential to the surface of the Earth.

Commercial FM broadcasting transmitter at radio station WDET-FM, Wayne State University, Detroit, USA. It broadcasts at 101.9 MHz with a radiated power of 48 kW.

Transmitter

Commercial FM broadcasting transmitter at radio station WDET-FM, Wayne State University, Detroit, USA. It broadcasts at 101.9 MHz with a radiated power of 48 kW.
A radio transmitter is usually part of a radio communication system which uses electromagnetic waves (radio waves) to transport information (in this case sound) over a distance.
Animation of a half-wave dipole antenna transmitting radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods, with an alternating current applied at its center from a radio transmitter (not shown). The voltage charges the two sides of the antenna alternately positive  (+)  and negative   (−) .  Loops of electric field (black lines) leave the antenna and travel away at the speed of light; these are the radio waves.  This animation shows the action slowed enormously
Hertz discovering radio waves in 1887 with his first primitive radio transmitter (background).
Guglielmo Marconi's spark gap transmitter, with which he performed the first experiments in practical Morse code radiotelegraphy communication in 1895-1897
High power spark gap radiotelegraphy transmitter in Australia around 1910.
1 MW US Navy Poulsen arc transmitter which generated continuous waves using an electric arc in a magnetic field, a technology used for a brief period from 1903 until vacuum tubes took over in the 20s
An Alexanderson alternator, a huge rotating machine used as a radio transmitter at very low frequency from about 1910 until World War 2
One of the first vacuum tube AM radio transmitters, built by Lee De Forest in 1914. The early Audion (triode) tube is visible at right.
One of the BBC's first broadcast transmitters, early 1920s, London. The 4 triode tubes, connected in parallel to form an oscillator, each produced around 4 kilowatts with 12 thousand volts on their anodes.
Armstrong's first experimental FM broadcast transmitter W2XDG, in the Empire State Building, New York City, used for secret tests 1934–1935. It transmitted on 41 MHz at a power of 2 kW.
Transmitter assembly of a 20 kW, 9.375 GHz air traffic control radar, 1947. The magnetron tube mounted between two magnets (right) produces microwaves which pass from the aperture (left) into a waveguide which conducts them to the dish antenna.

In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna.

A transmitter and a receiver combined in one unit is called a transceiver.

UHF half-wave dipole

Dipole antenna

UHF half-wave dipole
Dipole antenna used by the radar altimeter in an airplane
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).
Cage dipole antennas in the Ukrainian UTR-2 radio telescope. The 8 m by 1.8 m diameter galvanized steel wire dipoles have a bandwidth of 8–33 MHz.
Real (black) and imaginary (blue) parts of the dipole feedpoint impedance versus total length in wavelengths, assuming a conductor diameter of 0.001 wavelengths
Feedpoint impedance of (near-) half-wave dipoles versus electrical length in wavelengths. Black: radiation resistance; blue: reactance for 4 different values of conductor diameter
Length reduction factor for a half-wave dipole to achieve electrical resonance (purely resistive feedpoint impedance). Calculated using the Induced EMF method, an approximation that breaks down at larger conductor diameters (dashed portion of graph).
"Rabbit-ears" VHF television antenna (the small loop is a separate UHF antenna).
Collinear folded dipole array
A reflective array antenna for radar consisting of numerous dipoles fed in-phase (thus realizing a broadside array) in front of a large reflector (horizontal wires) to make it uni-directional.

In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna.

The driving current from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the two halves of the antenna.

Coherent waves that travel along two different paths will arrive with phase shift, hence interfering with each other.

Multipath propagation

Coherent waves that travel along two different paths will arrive with phase shift, hence interfering with each other.
A diagram of the ideal situation for TV signals moving through space: The signal leaves the transmitter (TX) and travels through one path to the receiver (the TV set, which is labeled RX)
In this illustration, an object (in this case an aircraft) pollutes the system by adding a second path. The signal arrives at receiver (RX) by means 
of two different paths which have different lengths. The main path is the direct path, while the second is due to a reflection from the plane.
Radar multipath echoes from an actual target cause ghosts to appear.
GPS error due to multipath
Mathematical model of the multipath impulse response.

In radio communication, multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths.

In radar processing, multipath causes ghost targets to appear, deceiving the radar receiver.

Erdfunkstelle, a large parabolic satellite communications antenna in Raisting, Bavaria, Germany, the biggest facility for satellite communication in the world. It has a Cassegrain type feed.

Parabolic antenna

Erdfunkstelle, a large parabolic satellite communications antenna in Raisting, Bavaria, Germany, the biggest facility for satellite communication in the world. It has a Cassegrain type feed.
Parabolic antennas are based on the geometrical property of the paraboloid that the paths FP1Q1, FP2Q2, FP3Q3 are all the same length. So a spherical wavefront emitted by a feed antenna at the dish's focus F will be reflected into an outgoing plane wave L travelling parallel to the dish's axis VF.
Wire grid-type parabolic antenna used for MMDS data link at a frequency of 2.5-2.7 GHz. It is fed by a vertical dipole under the small aluminum reflector on the boom. It radiates vertically polarized microwaves.
Main types of parabolic antenna feeds.
Array of multiple feed horns on a German airport surveillance radar antenna to control the elevation angle of the beam
Effect of the feed antenna radiation pattern (small pumpkin-shaped surface) on spillover. Left: With a low gain feed antenna, significant parts of its radiation fall outside the dish. Right: With a higher gain feed, almost all its radiation is emitted within the angle of the dish.
Radiation pattern of a German parabolic antenna. The main lobe (top) is only a few degrees wide. The sidelobes are all at least 20 dB below (1/100 the power density of) the main lobe, and most are 30 dB below. (If this pattern was drawn with linear power levels instead of logarithmic dB levels, all lobes other than the main lobe would be much too small to see.)
The angle theta is normal to the aperture.

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 to the receiver in its focal point.

In a receiving antenna the incoming radio waves bounce off the dish and are focused to a point at the feed antenna, which converts them to electric currents which travel through a transmission line to the radio receiver.

A typical mast radiator monopole antenna of an AM radio station in Chapel Hill, North Carolina. The mast itself is connected to the transmitter and radiates the radio waves. It is mounted on a ceramic insulator to isolate it from the ground. The other terminal of the transmitter is connected to a ground system consisting of cables buried under the field.

Monopole antenna

A typical mast radiator monopole antenna of an AM radio station in Chapel Hill, North Carolina. The mast itself is connected to the transmitter and radiates the radio waves. It is mounted on a ceramic insulator to isolate it from the ground. The other terminal of the transmitter is connected to a ground system consisting of cables buried under the field.
Showing the monopole antenna has the same radiation pattern over perfect ground as a dipole in free space with twice the voltage
Vertical radiation patterns of ideal monopole antennas over a perfect infinite ground. The distance of the line from the origin at a given elevation angle is proportional to the power density radiated at that angle.
Multi-lobed radiation pattern of 3⁄2 wavelength monopole. Monopole antennas up to 1⁄2 wavelength long have a single "lobe", with field strength declining monotonically from a maximum in the horizontal direction, but longer monopoles have more complicated patterns with several conical "lobes" (radiation maxima) directed at angles into the sky.
VHF ground plane antenna, a type of monopole antenna used at high frequencies. The three conductors projecting downward are the ground plane

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, or for receiving antennas the output signal to the receiver is taken, between the lower end of the monopole and the ground plane.