I am working on a AD9361 design with a customly designed AD9361 hardware. I am using STM32F407 to config AD9361. Basically it works well. But I found that the 2,3,4,5 harmonics are quite strong. as shown by the following to figures.
In the above figure, carrier is 600MHz, and you can see a strong harmonic of carrier at 1.2GHz
In the above figure, we set tx carrier to 80MHz, we can see a lot of harmonics.
My questions are : Where does the harmonics of carrier come from and how to get rid of? I am using a fully customed AD9361 hardware.
When I reduce Tx power, all the harmonics decreases correspondingly as with the carrier.