A stack of "fishbone" and Yagi–Uda television antennas
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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.
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.
Electronic symbol for an antenna
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.
Antennas of the Atacama Large Millimeter/submillimeter Array.
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.
An automobile's whip antenna, a common example of an omnidirectional antenna.
Representation of the electric field vector of a wave of circularly polarized electromagnetic radiation.
Half-wave dipole antenna
James Clerk Maxwell
Diagram of the electric fields ( blue ) and magnetic fields ( red ) radiated by a dipole antenna ( black rods) during transmission.
Electromagnetic spectrum with visible light highlighted
Cell phone base station antennas
Rough plot of Earth's atmospheric absorption and scattering (or opacity) of various wavelengths of electromagnetic radiation
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).
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In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves).

- Antenna (radio)

When any wire (or other conducting object such as an antenna) conducts alternating current, electromagnetic radiation is propagated at the same frequency as the current.

- Electromagnetic radiation
A stack of "fishbone" and Yagi–Uda television antennas

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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

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

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

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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.

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

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.

Circular polarization on rubber thread, converted to linear polarization

Polarization (waves)

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Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Circular polarization on rubber thread, converted to linear polarization
cross linear polarized
A "vertically polarized" electromagnetic wave of wavelength λ has its electric field vector E (red) oscillating in the vertical direction. The magnetic field B (or H) is always at right angles to it (blue), and both are perpendicular to the direction of propagation (z).
Electric field oscillation
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Animation showing four different polarization states and three orthogonal projections.
A circularly polarized wave as a sum of two linearly polarized components 90° out of phase
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Color pattern of a plastic box showing stress-induced birefringence when placed in between two crossed polarizers.
Paths taken by vectors in the Poincaré sphere under birefringence. The propagation modes (rotation axes) are shown with red, blue, and yellow lines, the initial vectors by thick black lines, and the paths they take by colored ellipses (which represent circles in three dimensions).
A stack of plates at Brewster's angle to a beam reflects off a fraction of the s-polarized light at each surface, leaving (after many such plates) a mainly p-polarized beam.
Stress in plastic glasses
Photomicrograph of a volcanic sand grain; upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter.
Effect of a polarizer on reflection from mud flats. In the picture on the left, the horizontally oriented polarizer preferentially transmits those reflections; rotating the polarizer by 90° (right) as one would view using polarized sunglasses blocks almost all specularly reflected sunlight.
One can test whether sunglasses are polarized by looking through two pairs, with one perpendicular to the other. If both are polarized, all light will be blocked.
The effects of a polarizing filter (right image) on the sky in a photograph
Colored fringes in the Embassy Gardens Sky Pool when viewed through a polarizer, due to stress-induced birefringence in the skylight
Circular polarization through an airplane plastic window, 1989

Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves (shear waves) in solids.

All radio (and microwave) antennas used for transmitting or receiving are intrinsically polarized.

HF's position in the electromagnetic spectrum.

High frequency

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HF's position in the electromagnetic spectrum.
A modern Icom M700Pro two-way radio for marine HF radio communications.
An amateur radio station incorporating two HF transceivers.
A typical Yagi antenna used by a Canadian radio amateur for long distance communication
Boeing 707 used a HF antenna mounted on top of the tail fin

High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz).

At worst, when a band is "dead", no communication beyond the limited groundwave paths is possible no matter what powers, antennas or other technologies are brought to bear.