Spurious emission on the second harmonic

Hi,

We are try to certificate a custom board with DW1000 chip on board. We have followed the application note APH001 for design the PCB and antenna layout. The last week we did a power spectral density test and we have seen some spurious emission on the second harmonic, like in the figure. In the Decawave documentation, there is no reference to the second harmonic and it is not even indicated to use a filter. Can anyone tell us something?

Thanks

Channel:2
Power settings
DA: 0 dBm MIX: 0 dBm

Channel:2
Power settings
DA: 6.0 dBm MIX: 6.5 dBm