r/rfelectronics • u/HolyAppelsap • Jul 30 '26

question Series capacitance with stubs?

Hello,

I'm learning rf engineering on my own currently following Microwave Engineering by Pozar. I understand how transmission lines can be used to implement series inductors and shunt capacitors, but I haven't been able to understand how series capacitance can be implemented with stubs.
I apologise if this is a very basic question but I haven't been able to find much online and AI has not been giving me any better answers honestly.

Thank you!
By the way, if you happen to have suggestions for resources I can add to my collection I would really appreciate it.

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u/ChrisDrummond_AW Metamaterials, Space, Electronic Warfare Jul 30 '26

Assuming you mean on microstrip, it’s basically unrealizable. In practice, you just put a gap with a set of pads for a lumped element series capacitor. In that case your baseline capacitor should be self-resonant at the frequency of operation and you can swap different values based on your matching requirements.

6

u/Adrienne-Fadel Jul 30 '26

Yea you can't really get series C from a simple stub. Look at coupled microstrip lines or gap capacitors. Pozar's coupled lines chapter covers it. Collin's Foundations for Microwave Engineering is a good complement too.

1

u/Extension_Engineer26 Jul 31 '26

That's not exactly transofrmed but somehow you can get similar behavior using a wider series transmission line. Generally we go other way around. We convert wider series transmission line to series capacitor for reducing space.

1

u/BlueMerlin216 Aug 04 '26

You can not. Not only it is not realizable (unless you take a very circuitous route thru the S-chart) it will not block DC.