Depends on which positive effects you want to achieve. For most applications, surely for radio transmitters, you want maximal attenuation of harmonics. That's basically regarded by selecting a low pass topology. But specific power stages, e.g. class C can have also requirements for the load impedance at harmonic frequency. Ultimately you place LC series circuits resonating at the harmonics.
dear FvM, again thank you very much.
I have a class A amplifier, and the effect I want is simultaneously having best performance for fundamental freq and offcourse maximal attenuation for the harmonics. I perfectly get that with lowpass design of the matching network it is possible.
But what arises question in my mind is more related to ADS design flow and guides that I have found.
The flow that I have seen (unfortunetly without clear explaination) is that, starting from fundamental freq, for example 'ZL' is the specific value that I find for optimum load, so far OK. As I precieve you responce, with a lowpass matching circuit I can finish the design right here.
But what I see instead, is that after finding 'ZL', the performance of system is again evaluated for both 2nd and 3rd harmonics, with sweeping the gamma phase (ofcourse around the edge of smith chart so considering the magnitude of reflection coefficient =1 ) and finding the optimum values for the load again!
There are 2 things that I absolutely don't get:
1- by this approach we will find 3 different load impedances for fundamental, 2nd and 3rd harmonic. now how to make a matching network compatible with these values in ofcourse these three different frequencies?
2- while performing the simulation for the 2nd, there is an option to put the optimum value of load impedance for fundamental frequency, I don't get how it could possibly effect the simulation result for the 2nd harmonic?? ( I did put different values and I observed different results).
I'm sorry for the long questions that I made, but unfortunetly I barely could have find convincing material on the web, and it is kindda driving me crazy.
I really appreciate for the time you spend to answer me.
Thank you.