In general belief, smaller capacitors have better charactristic(more capacitive behaviour) in high frequency than bulky capacitors.

On contrary in one of my RF project (8.5GHz - 9.5GHz) when checking for different package size as bypass capacitor between each of my microwave block (Mixer, Switches and etc) I suspect above rule of thumb

After some inspection on S-Param of Kemet RF capacitors, I noticed that for the same value of capacitor, SRF(Self Resonant Frequency) become higher as package size increases. So a 805 package have higher SRF than 603 and the same rule for 603 and 402 (SRF_603 > SRF_402).

I see the same result in KSIM simulator from Kemet. Here is the summarized result

10pF C0603 C0G 10VDC-8 C0603C100K8GAC : SRF = 2.089GHz

10pF C0805 C0G 10VDC-8 C0805C100K8GAC : SRF = 2.399GHz

As can be seen in simulator (and verified by VNA in lab) the SRF not decrease with size instead SRF increases with even more than 300MHz. Why is that the case?

  • note: I will add the sparam plot soon.
  • note2: I see same result in reply #11 and other replies on this page.
  • \$\begingroup\$ Show a photo of the internals of the test-jig you used to measure SRF. \$\endgroup\$ – analogsystemsrf May 10 '18 at 17:35
  • \$\begingroup\$ I dont have access to setup now. the test result is in compliant to kemet official result \$\endgroup\$ – pazel1374 Oct 12 '18 at 9:29
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    \$\begingroup\$ The "smaller size = higher self resonance" is a rule of thumb. If the self resonance is critical for your design, then you need to check to be sure (as you have done.) By checking the datasheet, you found that the general rule doesn't apply to a particular series of parts (perhaps because they were designed specifically for RF use.) \$\endgroup\$ – JRE Oct 12 '18 at 11:09
  • \$\begingroup\$ @JRE Thanks JRE, that seems a logistic answer. If you want you can post that as a answer so I could accept it \$\endgroup\$ – pazel1374 Oct 12 '18 at 11:46
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    \$\begingroup\$ If nobody posts an answer, I'll make that comment into an answer. I hope somebody more knowledgeable posts a better explanation and maybe explains the mechanism, though. \$\endgroup\$ – JRE Oct 12 '18 at 11:54

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