Notch filter reflect rejection_band power ?

I have a question regarding notch filter usage.
When I use notch filter, will the rejection band power bounce back to DUT?
Should I add Circulator or directional coupler between notch filter and DUT?
Thanks for suggestion

It depends on the kind of filter: dissipative or reflective.

With a dissipative filter you will have no problem.

With a reflective one and high power levels probably a circulator is preferred: It will help you to achieve a good match also.

Hi! marcodd ,
Can I say if the notch filter is dissipative then the S11 of the filter is close to 50 ohm.
On the other hand if the notch filter is reflective then the S11 of the filter is far from 50 ohm.
Could you give me some comment?
Thanks a lot

Filters with just reactive elements are reflective in the rejection band. You can make a diplexer which diverts the frequencies in the notch to a dummy load.

Alternately, you can include the notch in the transistor output network. Some of the high efficiency amplifier topologies use this method to square up the voltage waveforms while allowing a sinusoidal current waveform.

In general, a circulator is a good addition if you are in a high signal environment. It keeps RF power from near by transmitters coming back down the antenna-transmission line and causing IMD in your amplifier.