Dipole field strength in free space, in
telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
, is the
electric field strength
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field f ...
caused by a
half wave dipole
In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole w ...
under ideal conditions. The actual field strength in terrestrial environments is calculated by empirical formulas based on this field strength.
Power density
Let N be the effective power radiated from an isotropic antenna and p be the power density at a distance d from this source
:
Power density is also defined in terms of electrical field strength;
Let E be the electrical field and Z be the impedance of the free space
:
The following relation is obtained by equating the two,
:
or by rearranging the terms
:
Numerical values
Impedance of free space The impedance of free space, , is a physical constant relating the magnitudes of the electric and magnetic fields of electromagnetic radiation travelling through free space. That is, , where is the electric field strength and is the magnetic fie ...
is roughly
Since a
half wave dipole
In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole w ...
is used, its
gain over an
isotropic antenna (
) should also be taken into consideration,
:
In this equation
SI units are used.
Expressing the same equation in:
: kW instead of W in
power
Power most often refers to:
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power
* Power (social and political), the ability to influence people or events
** Abusive power
Power may a ...
,
:km instead of m in
distance
Distance is a numerical or occasionally qualitative measurement of how far apart objects or points are. In physics or everyday usage, distance may refer to a physical length or an estimation based on other criteria (e.g. "two counties over"). ...
and
:mV/m instead of V/m in
electric field
is equivalent to multiplying the expression on the right by
.
[ K.H.Kaltbeitzer: ''Site selection'', EBU Techhnical Monograph 3104,Bruxelles,1965, p 30 ] In this case,
:
:
See also
*
Antennas
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. In transmission, a radio transmitter supplies an ...
*
Effective radiated power
Effective radiated power (ERP), synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency (RF) power, such as that emitted by a radio transmitter. It is the total power in watts that would h ...
*
Electric field
*
Field strength meter
In telecommunications, a field strength meter is an instrument that measures the electric field strength emanating from a transmitter.
The relation between the electric field and the transmitted power
In ideal free space, the electric field stre ...
*
Radio propagation model
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere.
As a form of electromagnetic radiation, like light waves, radio waves are affected ...
References
{{Radio frequency propagation models
Telecommunication theory
Antennas
Broadcast engineering
Radio frequency propagation model