Cap between collector and emitter

This is the schematics of the microwave amplifier. I would like to ask there were two capacitor C21 and C22. What is the functions of these two capacitors?

Moreover, for the RF choke L13, how to calculate the inductance of the inductor?

Thank you very much

It is a low frequency RF "tuned" amplifier--that is, narrow bandwidth gain. This is typical of the type of amplifier Hams used to use 20 years ago.

C22 is just a capacitor to ground.

C21 resonates with the inductor to form a "parallel resonant" tank circuit. At resonance, the capacitance cancels the inductance, and there is an RF high impedance between the collector and the power supply.

The inductor is a 3 turn inductor. You would need to know its actual dimensions to figure out the intended inductance. If it is a surface mount coil, just go to coil craft and look up a 3 turn coil for a guess.

In fact this is a simple VHF amplifier, but the reason why looks so complicated is because whoever draw the schematic was in a big hurry.

Resonance frequency is approximately 290MHz (I have assumed that L13 has around 20nH inductance value )
I guess it's is an amplifier that operates at 300MHz...