Electronic – Transmission Line Question

hflinereflectiontransmission

I have a question concerning reflections due to impedance mismatching. Now, assuming a lossless TL, the latter is modelled by sections of lumped L-C segments where L in a series (sub)element of the transmission line and the capacitors connect to GND. I understand that this models the two wires of the TL and mathematically leads to the characteristic impedance Sqrt(L/C) used to calculate reflections once source and load impedances are also known.. Now to my question.. I know how to compute the reflection coefficient when source and load impedances are given. But how do i calculate the reflection introduced by a series capacitance in the TL, right between the source and the TL? (Or between TL and the load). I assume i have to include the series C into source or load, respectively…but how to deal then (for example) when there are two TLs in series and the series C is right between those?

Thanks a lot for explanations 😉

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Best Answer

You can solve any simple TL problem like this :

  1. start at the load, and work towards the generator.
  2. take the end load Z (if it's a reactance, convert to Z using frequency)
  3. Transform the impedance down the line, either using a Smith chart, the TL equation or the lossless TL equation.
  4. If you have a series capacitor in the middle of a line, treat it as two lines. Calculate Z up to the cap, then add 1/jwC, then carry on.
  5. If you're looking for reflection coefficient of the whole complex circuit, Load, TL, capacitor, TL, then just convert back from impedance.
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