RF cable and Smith Chart

Hi all,

Can any body explain me that why the 50 Ohm cable only makes the S parameter shift on Smith Chart?

Hi

This is because it only change the phase. Not the amplitude (if lossless/low loss).

Regards

Do not think about this question by the function of impedance. it's too complex. In Smith chart, the x-coordinate and y-coordinate can be real part and imaginary part of reflection coefficient.
and the Γin=Γ0*E(j*β*d)
where Γ0 is the reflection coefficient at the load end of the microstrip,
Γin is the reflection coefficient at the other end.
d is the length of the microstrip
so as d is changing, the track of Γin is a circle.
Γ0 =(Zl-Z0)/(Zl+Z0)
the central of the circle is Z0, the radius is the distance between Γ0 and Z0 at x-coordinate.

Hi

The input reflection coeffcient should read: Γin=Γ0*E(2*j*β*d)
The 2 takes into account that the wave have to travel down the transmission line and back to the source.

Regards