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Its presently accepted value is [1] Z 0 = 376.730 313 412 (59) Ω, where Ω is the ohm, the SI unit of electrical resistance. 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.
where c is the defined value for the speed of light in classical vacuum in SI units, [4]: 127 and μ 0 is the parameter that international standards organizations refer to as the magnetic constant (also called vacuum permeability or the permeability of free space). Since μ 0 has an approximate value 4π × 10 −7 H/m, [5] and c has the ...
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),
Permittivity as a function of frequency can take on real or complex values. In SI units, permittivity is measured in farads per meter (F/m or A 2 ·s 4 ·kg −1 ·m −3 ). The displacement field D is measured in units of coulombs per square meter (C/m 2 ), while the electric field E is measured in volts per meter (V/m).
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,
The permeability of vacuum (also known as permeability of free space) is a physical constant, denoted μ 0. The SI units of μ are volt-seconds per ampere-meter, equivalently henry per meter. Typically μ would be a scalar, but for an anisotropic material, μ could be a second rank tensor.
Another frequently used value for determining ... is a universal constant called vacuum impedance or impedance of free space. The equivalent circuit and the formula ...
For small values of r / λ the impedance is high and capacitive, at short range being asymptotic to: | | . In both cases, the wave impedance converges on that of free space as the range approaches the far field.