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
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 . In this case,
See also※
- Antenna (radio)
- Effective radiated power
- Electric field
- Field strength meter
- Radio propagation model