Dipole field strength in free space
Dipole field strength in free space, in telecommunications, is the electric field strength caused by a half wave dipole 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[1]
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 is roughly
Since a half wave dipole 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,
- km instead of m in distance and
- mV/m instead of V/m in electric field
is equivalent to multiplying the expression on the right by .[2] In this case,
See also
- Antenna (radio)
- Effective radiated power
- Electric field
- Field strength meter
- Radio propagation model
References
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