I seem to remember that the shorted- vs open-transmission line reflection is out of phase by 180-degrees. I'm new to the mathematics behind transmission line theory and I'm trying to figure out how that phase shift is represented in the scattering matrix.

I couldn't find a reference for this, hence this question, so please correct me if I'm wrong: I am guessing the S-parameters for an ideal open-circuit and ideal transmission line are as follows. The values are in dB format, so "0" means no loss:

Ideal Transmission Line

S11: -INF+0j   S12: 0+0j
S21:    0+0j   S22: -INF+0j

Ideal Open Transmission Line (ie, its been cut but is not shorted)

S11:    0+0j   S12: -INF+0j
S21: -INF+0j   S22: 0+0j


  • What are the S-parameters for an ideal transmission line that is:
    1. Shorted at one end?
    2. Open at one end?
    3. Are #1 and #2 represented purely as S11? It doesn't sound like S21 would play a part here.
  • Does \$Z_0\$ play any part in the "ideal" case?

I would be interested to understand how the math for how this trivial circuit is represented to calculate the resulting S-parameter matrix. If you know the details then a bit of help understanding the math to create the resulting matrix would be appreciated.

  • \$\begingroup\$ What length of t-line? \$\endgroup\$
    – Andy aka
    Jul 8, 2022 at 8:10

1 Answer 1

  1. s11=0
  2. s11=0
  3. Y.
    . N

If the other end cannot be accessed then only s11 is relevant.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.