Dipole field strength in free space

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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[edit]

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 R be the impedance of the free space

The following relation is obtained by equating the two,

or by rearranging the terms

Numerical values[edit]

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[edit]

References and notes[edit]

  1. ^ Reference data for radio Engineers, Howard W.Sams co,Indianapolis, 1956, 27-7
  2. ^ K.H.Kaltbeitzer: Site selection, EBU Techhnical Monograph 3104,Bruxelles,1965, p 30