how to reduce harmonic products

You will have to use a very linear type amplifier. It should be followed by LC filters that are tuned in real time to track the frequency in use.

Output of the PA(1~30M),
P-1=43dBm, 2nd harmonic =-40dBc,3rd harmonic=-22dBc,
But the Imd3=-17dBc,how to increase the IMD3?
thanks

Don't run the PA anywhere near compression, this will increase the IM products drastically.

I have designed predistorters to reduce 3rd order intermodulation products. Without trying too hard, they can reduce IM products by 9 dB, and much more if you work at it.

I can not think of any reason you could not use a predistorter to reduce the 2nd harmonic out of a power amp too. It would be a different design--one that operated with 2nd order products.

Rich

use the balanced circuit to minimize the harmonics.

you see you want better 2nd hamonic than the 3rd. So there really is a way to reduce 2nd hamonic but the 3rd.