Electrical length

In the high-frequency technology, the electrical length is the length of a transmission medium, expressed as a multiple of the wavelength (symbol λ ) of a periodic signal, which propagates in the medium (see line theory ). The electrical length is often given in units of radians.

Electromagnetic waves propagate slower in a medium or on a waveguide (such as an antenna cable), as they would do that in a vacuum. It follows that their wavelength in a medium is less than it would be in a vacuum. For the mechanical dimensions of lines and resonators (for example, antennas), this means that they are mechanically usually smaller than it would be after the calculation from the frequency and the vacuum speed of light.

For example, the telescope antennas of many portable radios are about 75 cm long and have thus relative to the wavelength of 3 m of the FM broadcasting a length of 1 /4 of the wavelength. Shorter rod antennas, as they are often seen on cars are electrically shortened by special measures ( longitudinal induction by coiling ) and also have an electrical length of λ / 4 The electrical length of antenna can also be extended through appropriate measures.

In waveguides such as coaxial cables, the term reduction factor is used occasionally. It indicates the factor by which the conductor is shorter than the calculation from the vacuum speed of light would be expected. This information is, for example, for the calculation of stubs of importance.

• Electromagnetic Theory
• Electrical conduction