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The impedance of free space (that is, the wave impedance of a plane wave in free space) is equal to the product of the vacuum permeability μ 0 and the speed of light in vacuum c 0. Before 2019, the values of both these constants were taken to be exact (they were given in the definitions of the ampere and the metre respectively), and the value ...
In free space the wave impedance of plane waves is: = (where ε 0 is the permittivity constant in free space and μ 0 is the permeability constant in free space). Now, since = = (by definition of the metre),
Impedance of free space is roughly Since a half wave dipole is used, its gain over an isotropic antenna ( 2.15 dBi = 1.64 {\displaystyle {\mbox{2.15 dBi}}=1.64} ) should also be taken into consideration,
= = is a universal constant called vacuum impedance or impedance of free space. The equivalent circuit and the formula at right are valid for any type of antenna. It can be as well a dipole antenna, a loop antenna, a parabolic antenna, or an antenna array. From this formula, it is easy to prove the following definitions:
The wave impedance is the ratio of the strength of the electric and magnetic fields, which in the far field are in phase with each other. Thus, the far field "impedance of free space" is resistive and is given by:
Feedpoint impedance of (near-) half-wave dipoles versus electrical length in wavelengths. Black: radiation resistance; blue: reactance for four different values of conductor diameter. A true half-wave dipole is one half of the wavelength λ in length, where λ = c / f in free space. Such a dipole has a feedpoint impedance consisting of ...
Larmor formula; Lenz law; ... Impedance; Inductance; Joule heating; ... where ε 0 is the permittivity of free space and μ 0 the permeability of free space. Since ...
Vacuum permittivity, commonly denoted ε 0 (pronounced "epsilon nought" or "epsilon zero"), is the value of the absolute dielectric permittivity of classical vacuum.It may also be referred to as the permittivity of free space, the electric constant, or the distributed capacitance of the vacuum.