Specifications

D-2

When a (virtual) transmission line in which the signal wavelength is equal to the wavelength in a

vacuum is assumed, the virtual line length ( e) that causes the same phase shift (β ) as in the actual

line is given by the following equation:

λo 2π 2π e

e = ——— (because β = ———— = —————— )

λλλo

Where, λo is a wavelength in vacuum

λ is a wavelength in transmission line

Therefore, the phase shift quantity, β , can also be expressed by using the phase constant βo in vac-

uum and the virtual line length e (because β = βo e.) Since the βo value is derived from physical

constants (βo = 2π/λo = ω/c, c: velocity of light), it is possible to represent the phase shift by using

only the virtual line length e.

This virtual line length is specified as the electrical length of the test fixtures and airline extensions.

Accordingly, the compensation procedure to derive the impedance Z

can be simplified by using the

electrical length value. In case of the coaxial line, since the β value is proportional to √

—

C (C: distrib-

uted capacitance of the line), the electrical length is proportional to the square root of the dielectric

constant of the insulation layer between the inner and outer conductors.