pa saturation

If we drive PA output(3W class A rf power amp ) into saturation, is it have bad effect on rf fsk modulated signal? can we drive PA into saturation during normal operation to use its max power output?

FSK is not impaired by saturated power amp.

True: FSK is constant envelope so don't bother AM/AM or AM/PM.

How ever you may need to comply the emission standards so better not to over drive much.

kspalla:

Do you mean that second and other harmonics of PA output becomes stronger?

If I push the PA in heavy saturation then the output harmonics will be increased then we have to use LPF filter.

Yes.
LPF with cutoff below second harmonic frequency or BRF which is easy than LPF.

minicircuits have smd small LPF filters (high watt) that are suitable for harmonic rejection,

I want to push the PA into saturation and use the minicircuits LFCN serie filters,I think this is a good way.what is your idea?

LPF will give more IL if the order of the filter is more.
if the order is less then you will get less attenuation for the second harmonic.
BTW what is your specification on this?
BRF will be easy to implement if the freq is in GHz.
What's your Freq of operation?

IL of minicircuits is 0.6db,Is it good? Have BRF lower IL?what is its value?

Can you send info on BRF?

f=1800MHZ

IL of the order 0.4 dB should be ok. 0.6dB also fine if the amplifier takes care of this loss.
How ever IL is not the only parameter. In this case, it is associate with the rejection of the filter too.
What is the rejection requirement?
BRF is generally notch filter in this case.
Depend on the BW we need to go for multiple fingers.
I feel a 4 finger BRF will be sufficient.

I need 30dB rejection and LFCN give this.

How to design BRF? Is there any help on design it? Please send some links.