Capacitor, Series Resonance in ISM band

[trevorth]

I have a simple ISM transceiver and its output through a couple of RF switches. In between these switches I have DC blocking capacitors.

I need to make sure that the impedance is low at 2.4-2.5GHz. Looking at a datasheet E.g.
**broken link removed**
Page 2 - Plot ' Frequency characteristics (ESR, Impedance) '

It seems as though Z at 2.4Ghz will be around 40ohm. Am I going about this the correct way / am I missing something?

Id ideally use F=1/(2PI*sqrt(LC)) but the manufactures dont seem to give inductance figures....

 

[rfmw]

You're right. You should consider using a higher value of capacitance. See this link:

https://www.johansontechnology.com/...r-capacitors-rohs/series-resonance-chart.html

A value of about 10-22pF should have a series resonance at 2.5GHz.


You can back-calculate the series inductances of capacitors using this chart as well.

 

[trevorth]

Thanks, most helpful

 

[rfmw]

In addition to that graph, I've taken the measured S-parameter data of various capacitors also available on Johansontech website and looked at the minimal insertion loss from the S21 trace. In this way you can be sure to mount the correct/optimal capacitance value into your circuit.