Less Line, Standing Waves, Nodes, Standing Wave Ratio

LESS LINE, STANDING WAVES, NODES, STANDING WAVE RATIO

If the transmission is not terminated in its characteristic impedance ,then there will be two waves traveling along the line which gives rise to standing waves having fixed maxima and fixed minima.

The ratio of the maximum to minimum magnitudes of current or voltage on a line having standing wave is called the standing-wave ratio S. That is, S= E _max = I _max; E_min =I _min.

For coaxial lines it is necessary to use a length of line in which a longitudinal slot, one half wavelength or more long has been cut. A wire probe is inserted into the air dielectric of he line as a pickup device, a vacuum tube voltmeter or other detector being connected between probe and sheath as an indicator. If the meter provides linear indications, S is readily determined. If the indicator is non linear, corrections must be applied to the readings obtained.

The relation between standing wave ratio S and reflection co-efficient k is, S =1+ k/1-k.