71082

Voltage standing wave ratio

We recall from Chapter 2 the results S =

Rmax

Zo

= rmax(3.7)

s =

Zo

Rmin 1

fmin

(3.8)

and the fact that the point of maximum voltage on the linę occurs as the point of maximum impedance and the point of minimum voltage on the linę occurs at the point of

minimum impedance, and that those points are distant a quarter of a wave length apart.

These matters are illustrated in Figurę 3.7 which shows the locus of a voltage reflection

factor, which originates from a point at which the normalised load impedance is zi, as we move back along the linę away from the load.

When that locus intersects the horizontal axis to the right of the origin, the voltage reflection factor has become real and positive, and maximum voltage and impedance occur at that point. Moving further along the linę away from the load produces a second

intersection of the horizontal axis, this one to the left of the origin, at which point the voltage reflection factor has become real and negative, and the point of minimum voltage

and impedance is encountered. We see that the movement from the point zitowards the

input end of the linę passes through points of voltage maximum and minimum on the linę, as shown in Figurę 3.7.