Does an increase in frequency affect a capacitors value?

Question

When looking at an open circuited microstrip line, when the frequency is increased the value of the capacitance is changed.

When looking at an ideal capacitor the value does not change with increased frequency.

If it wasn't an ideal capacitor would the value change?

yes, for example [see here](https://electronics.stackexchange.com/questions/327975/capacitance-vs-frequency-graph-of-ceramic-capacitors) — Pete W, Mar 16 '21 at 02:45
Also for ceramic capacitors (mlcc) the effective capacitance changes over temperature and voltage bias — Ernesto, Mar 16 '21 at 03:31
Real capacitors get inductive after a certain frequency, (inductors, the same after resonance), have piezo and biase effects and also you have all the parasitic LC components from your circuit boards. In UHF even nanohenries and picofarad matters. So either you have a really good simulator or simply tune the values after building. If you are using RF rated capacitor at least many of these issues are attenuated — Lorenzo Marcantonio, Mar 16 '21 at 07:06

score 2 · Accepted Answer · answered Mar 16 '21 at 06:50

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If your circuit has to work, let's say, at 2.4 GHz, then you have to carefully pick capacitors and inductors that have resonant frequency above 2.4 GHz, for example 3 GHz.

This is the standard way to design RF circuits.

Murata and others characterize their components in frequency.

answered Mar 16 '21 at 06:50

Enrico Migliore

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After that the golden rule is buy borrow or steal a VNA and a trained operator or simply be happy with whatever comes out. That's my experience even for small RF circuits (mostly antenna feeds) – Lorenzo Marcantonio Mar 16 '21 at 07:08
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@LorenzoMarcantonio Asking is not an option. Assert your dominance. – DKNguyen Mar 16 '21 at 08:02

score 2 · Answer 2 · answered Mar 16 '21 at 07:05

Yes the capacitance change with the frequency:

The dielectric constant is a function of frequency. Depending on the material used this could be negligible others may be problematic.
There is a series inductance of the capacitor. So the realcapacitor is a series L-C circuit.

Does an increase in frequency affect a capacitors value?

2 Answers2