# `Intrinsic Impedance`

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 The intrinsic impedance is a property of a medium - an area of space. For a vacuum (outer space) or for wave propagation through the air around earth (often called 'free space'), the intrinsic impedance (often written as or Z) is given by: = This parameter is the ratio of the magnitude of the E-field to the magnitude of the H-field for a plane wave in a lossless medium (zero conductivity): This relation can be derived directly from Maxwell's Equations. For a general medium with permittivity and permeability given by , the intrinsic impedance is given by: For a medium with a conductivity associated with it, the intrinsic impedance is given by: When the conductivity is non-zero, the above intrinsic impedance is a complex number, indicating that the electric and magnetic fields are not in-phase. The intrinsic impedance of free-space has nothing to do with the electrical impedance of an antenna. Also, there is no reason to have the impedance of an antenna match the intrinsic impedance of free space (no mismatch loss occurs).