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For wireless product such as Bluetooth (2.4GHz), DC blocking cap for RF circuit is in the region of 5.6 to 10pF. I use a lot of 6pF, COG tolerenace, 0402 ceramic cap from MURATA, ACX, Epcos.
The trick is to such a cap that has a series resonance frequency around the working frequency of your RF circuit. 8)
Make the value of the DC-blocking capacitor as low as possible, without introducing additional RF loss/voltage drop in your circuits. Calculate the reactance as Xc = 1/(2*pi*f*C).
The self resonance of the capacitor vill generally be higher with lower capacitance value.
The DC blocking cap will function as a high-pass filter as well. The corner frequency will increase with decreased cap value, which is desirable in some cases.
You can model the equivalent circuit (simple 1 will do) in microwave simulator and therefore understand what is the best value to use as DC block.
Juse be careful with the self resonant frequency is high enough from ur operating frequency and equivalent series resistance is low at ur operating frequency.
For more comprehesive understanding, check out here
**broken link removed**
at high microwave frequencies it is good if you can find cheep and adequate DC blocking capacitor. Sometimes onli beam-lead capacitors are available and they might be too expencive and require special mounting techniques. In that situation it is best to use coupled lines in microstrip or some other structure to form BP filtering structure that acts as a DC block.
Finding the C value is easy. I agree with most reply.
I may another little source of info: AppCad by Agilent.
But pratically speaking, sefl inductance, both inside and outside the capacitor otfen limit the BW of the circuit.
A solution may by an "inverted koala" were a small capacitor connected to the circuit is surmounted by a larger one connected parallel.
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