# Choosing capacitor for RF coupling

I want to couple 10W at 150MHz, 50 Ohms (before and after an RF switch). The PA is a RA08H1317M powered by 14V DC.

How do I choose an RF coupling capacitor?

I have found this answer, but it only applies to the frequency, not power. What power rating can I expect from an 0805 or 1206 MLCC?

• um, what impedance does your system have / what's the peak voltage across that cap? Commented Dec 16, 2017 at 19:54
• I have updated my question. I don't know the exact RF voltage. The PA is powered from 14V.
– filo
Commented Dec 16, 2017 at 20:27

At page 7, on the equivalent circuit of the RA08H1317M, the output is already AC coupled. Same thing on page 1 on the block diagram.

If you need to AC couple outside of the component anyway, then you have to find the power dispated by the capacitor due to ESR:

$P_{cap}=R_{ESR} \cdot I^2=\frac{R_{ESR}}{R_{50Ω}} \cdot P_{RF}<\frac{0.1Ω}{50Ω} \cdot 10W=20mW$

This is close to the typical power rating for size 0603. Size 0805 and 1206 should have no problem if you asume an ESR below 100mΩ. You should probably use a NPO dielectric.