# How to convert lumped components to TL segments?

I have the following circuit:

which I need to implement in Microstrip. For now in order to get the correct results I was using lumped capacitors. But I will need to use Microstrip stubs when fabricating the board. How can I convert the circuit into one using stubs instead of these lumped elements.

• What are you actually trying to accomplish? For example, are you trying to make a low-pass filter? Or some kind of coupler? Or a balun? Or what? – The Photon May 22 '19 at 16:56
• I am trying to make a directional coupler. – hacker804 May 22 '19 at 17:04
• What frequency band? – The Photon May 22 '19 at 17:13
• 2-4GHz, with a center frequency of 3GHz. – hacker804 May 22 '19 at 17:15
• For that band and ~0.2 pF, I would expect you could use discrete capacitors. You might get eaten alive by tolerances though. – The Photon May 22 '19 at 17:24

• @hacker804, probably not. There are formulas (I think) for coplanar plate capacitors, which would be a better fit. But you could just add another coupled line segment to your ADS model and optimize on the S parameter instead. Given that your separation is already down to 0.13 mm for the closely coupled segment, you might not be able to get much closer (maybe 0.075 mm) if this is a ordinary PCB. If this is a thin film circuit you can probably get much closer. – The Photon May 22 '19 at 19:57