imd rf
Thanks to all for the responses.
Yes in effect, my hypotheses (I don't make theoretical calculations nor simulations yet) were in these directions: first about harmonic matching, and second bilaterality of the amplifier because I designed a very linear driver (< -50 dBc of intermod), then I watch power efficiency for estimate the matching and IMD between the driver and power stage.
Having a good matching (good matching means good efficiency/gain/gain flatness compared with theoretical) between stages and good matching in the power stage for the band of interest to 50 Ohm resistive load, I observed a rise of shoulders phenomena in the driver, this raise phenomena is mainly in the push-pull stage rather than single transistor stage, that may be because push-pull is "more bilateral" and this produces the called "reverse intermodulation products" effect.
I'm thinking to try the measurement with circulators but, I haven't expensive VHF circulators, and self-made circulator implies looking for anisotropic ferrites and waste more time..., so I will try the following thing:
In the final design two power stages in parallel wil be connected via 3dB quadrature Hybrid, is well known that one property of these hybrids is "two loads reflection coefficient masking effect" if the loads are the same. I think that the bilaterality (if the amplifier is stable), can be seen as load charge modulation by the driver, so, reflection coeffient modulation and therefore reverse IMD produtcs appears. If the two stages are equal, and they are connected by quadrature hybris, may be global linearity improvement...
What do you think about this?
I didn't speak yet about matching harmonics, but I belive this is also a tricky task, and they must be dissipated in an alternative load.
Added after 12 minutes:
P.S: Sorry for forget the other suggestions, about the matching is broad band. The coupling of power was made with lots of low ESR capacitors and good RF capacitors, (the test was also performed in a freescale evaluation board). The power source is a good laboratory source capable of handling 60V-50Amp. I adds extra ferrite beads to DC power, polarization and coaxial-RF cables and made EMC tests for induced and radiated.