Earth-Ionosphere waveguide
Encyclopedia
The Earth–ionosphere waveguide refers to the phenomenon in which certain radio waves can propagate
in the space between the ground and the boundary of the ionosphere
.
Because the ionosphere contains charged particles, it can behave as a conductor
. The earth operates as a ground plane
, and the resulting cavity behaves as a large waveguide
.
Extremely low frequency
(ELF) and Very low frequency
(VLF) (300 Hz
– 30 kHz) frequency signals can propagate efficiently in this waveguide. For instance, lightning strikes launch a signal called radio atmospherics, which can travel many thousands of miles, because they are confined between the Earth and ionosphere.
The round-the-world nature of the waveguide produces resonance
s, like a cavity, which are at ~7 Hz.
Radio propagation
Radio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere...
in the space between the ground and the boundary of the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
.
Because the ionosphere contains charged particles, it can behave as a conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
. The earth operates as a ground plane
Ground plane
In electrical engineering, a ground plane is an electrically conductive surface.-Radio antenna theory :In telecommunication, a ground plane structure or relationship exists between the antenna and another object, where the only structure of the object is a structure which permits the antenna to...
, and the resulting cavity behaves as a large waveguide
Waveguide
A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave...
.
Extremely low frequency
Extremely low frequency
Extremely low frequency is a term used to describe radiation frequencies from 3 to 300 Hz. In atmosphere science, an alternative definition is usually given, from 3 Hz to 3 kHz...
(ELF) and Very low frequency
Very low frequency
225px|thumb|right|A VLF receiving antenna at [[Palmer Station]], Antarctica, operated by Stanford UniversityVery low frequency or VLF refers to radio frequencies in the range of 3 kHz to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals...
(VLF) (300 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
– 30 kHz) frequency signals can propagate efficiently in this waveguide. For instance, lightning strikes launch a signal called radio atmospherics, which can travel many thousands of miles, because they are confined between the Earth and ionosphere.
The round-the-world nature of the waveguide produces resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
s, like a cavity, which are at ~7 Hz.
See also
- Radio propagationRadio propagationRadio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere...
- SkywaveSkywaveSkywave is the propagation of electromagnetic waves bent back to the Earth's surface by the ionosphere. As a result of skywave propagation, a broadcast signal from a distant AM broadcasting station at night, or from a shortwave radio station can sometimes be heard as clearly as local...
- Shortwave radio
- Tropospheric ducting
- Atmospheric ductAtmospheric ductIn telecommunication, an atmospheric duct is a horizontal layer in the lower atmosphere in which the vertical refractive index gradients are such that radio signals are guided or ducted, tend to follow the curvature of the Earth, and experience less attenuation in the ducts than they would if...
- WaveguideWaveguideA waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave...