I'm setting up an S-Parameter test on a transmission line, but I want the electrical length to change and depend on the frequency. How can I go about that? The variables that I can put in are all constant-I can't figure out how to make non-constant variables. I also tried putting in a sweep plan, but I can't figure out how to use it as a variable in the transmission line.
Electrical – In ADS, how can I change the electrical length on a transmission line to depend on the frequency sweep
adstransmission line
Related Solutions
Continuous varying impedances are used all the time for impedance matching. If you have a very capacitive part of a trace (for example, where a large component pad might be), you can have a relatively inductive transition before or after it to "balance" it out.
What will end up happening is that the reflections will "stack up" but, instead of being at one point (a VSWR peak), it will be moderately spread out. You can still imagine it discretely, but in small steps.
And also remember, if you have a small reflection point, any backward reflection after THAT will be reflected slightly FORWARD, and so on.
Anyway, the good gents at http://www.microwaves101.com/encyclopedia/klopfenstein.cfm always have a nice, in depth explanation.
edit: I didn't completely answer your question. "How it would look" is dependent a bit on how you are describing it. In the frequency domain, what you'll probably get is a VSWR that is "de-Q'd". You'll go from a nice sharp peak at midband to a more gradual, broader band response.
In the time domain....well, I don't work with the time domain as much but I would imagine you would have a lower amplitude, longer pulsewidth "ringing" or reflection.
Electronic – Must the characteristic impedance of a transmission line be non-real for it to be lossy
Phil, the real part of the propagation constant is the attenuation constant and this equals: -
\$Re\sqrt{(R+jwL)(G+jwC)}\$ and not the formula you have in your question.
The formula you have used is for characteristic impedance.
This wiki page should confirm this (right at the bottom): -
So, if you do the math at low frequencies (to make life easier) you see that the attenuation constant becomes \$\sqrt{RG}\$ and if R=G=1 then you have a constant of 1 and a lousy highly lossy line. A lossless line has a re(propagation constant) of zero.
Best Answer
This effect is called dispersion, and ADS is able to model it. However, you might have trouble with it. The way that dispersion works is limited by the laws of physics, and the ADS simulator attempts to obey these laws. The consequence is that electrical length versus frequency cannot change in an arbitrary way. Using ADS for this type of analysis requires an understanding of dispersion and how it is constrained. This is an advanced topic. Start with the Kirschning and Jansen formula.