I am working on impedance matching for one of my projects. After studying different stub matching strategies, I have implemented single and double stub successfully. When I use just a line and a stub (configuration shown in figure 1) I get very good results. But when I use a T-junction-connector (recommended to use when to connect two micro-strip lines, see figure 2) my results degrade by a significant value. I am using ADS for the design. My questions are:

1) Is it mandatory to use the connector component? 2) If it is mandatory? how to assign dimensions to this component?

enter image description here

enter image description here


Thank you for the help!

  • \$\begingroup\$ I'm not sure I understand the relevance of the back story to the question and the real problem you have. \$\endgroup\$
    – Andy aka
    Feb 25 '17 at 11:53
  • \$\begingroup\$ Can you implement a stub without a junction on any physical structure? \$\endgroup\$
    – Mike
    Feb 25 '17 at 11:54

You will often be able to get better results in simulation if you model something simpler than the real world. However, the purpose of using simulation is not to get good simulation results, but as a step to getting good real world results. That means modelling everything as faithfully as you can.

When you join transmission lines of different widths in the real world, there is a discontinuity, which is modelled by that 'Tee' piece that's upsetting your nice simulation results.

The way ADS models lines is that they connect without discontinuity. That means the top picture you have there isn't finished. It's not a good model of anything. If you want a good model, you have to add the Tee.

The reason that we add a Tee manually is that there are different models for Tees, some simple and inaccurate, some more complicated and better, or you might want to use a measure S-parameter file, and all depending on the physical construction of the lines. That's why ADS doesn't assume a discontinuity when you connect dissimilar lines.

Why does it let you draw a circuit without them, like the top one? I don't know, I've never really thought about it, though I have often used ADS in a quick and dirty mode where it didn't matter so much, and I was allowing for the effects. Why shouldn't it let you simulate exactly what you draw? You alone know how well your real world is modeled.

If you leave it out of your simulation, and build what you think you've modeled, you're in for a disappointment.

How to dimension it? Look up the instructions for that component. You usually match line widths, but of course you need to specify them in the right order. You'll probably need an extra MLIN between your TERM and your MTEE.

  • \$\begingroup\$ Thank you for your response @Neil_UK, it is very helpful! Now, I understand the importance Tee component. \$\endgroup\$
    – voyager
    Feb 28 '17 at 4:39
  • \$\begingroup\$ I am trying to implement the structure as told by you, adding an extra line before "term" was really helpful while creating a layout of the circuit. But, adding MTEE is creating issues. Is "MTEE" needed when the widths of the lines are equal? \$\endgroup\$
    – voyager
    Mar 1 '17 at 9:46
  • \$\begingroup\$ MTEE is always needed, whether the lines are equal width or not. What 'issues' is it creating? If you don't want to use the furnished MTEE, you could always scope out the effect of omitting the model by, in the very simplest case, putting a small C to ground at the three way junction of the lines, and varying the C to see what sort of errors an unmodelled shunt C at this point could cause. If doing that causes the same 'issues' as using the MTEE, then that's just telling you that the topology you've chosen won't work in practice, even though a simplified version works in simulation. \$\endgroup\$
    – Neil_UK
    Mar 1 '17 at 9:52
  • \$\begingroup\$ Okay got your point. By issues, I mean the matching is improper and because of improper matching it does not give me maximum power transfer. Thank you! :) \$\endgroup\$
    – voyager
    Mar 1 '17 at 9:59
  • \$\begingroup\$ Try using a radial stub rather than a constant width line stub. I understand they model better. \$\endgroup\$
    – Neil_UK
    Mar 2 '17 at 9:08

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