CC2538-CC2592EM-RD: 1.2GHz and harmonics seen on 2.4GHz output

Hi,

We have a board that copies the reference design as closely as possible with the exception that the SMA SMT connector was changed to a through-hole mount to reduce breakage.  

The SMA connector has the same size above the board, with the addition of through-hole pins where the surface mounts were.

A Pulse W1038G mono-pole antenna is mounted directly to the SMA connector, normal to the PCB

Problem: When transmitting, there are spurious harmonics of half the carrier frequency present.

Here, Marker 1 is the expected 2.475GHz carrier; Marker 2 is on the half-frequency spur and Marker 3 is on the third harmonic of that.

What are possible causes of these?  

Is it possible the PLL is falling out of lock?  In this case I would expect to see ±1MHz and harmonics modulated onto the carrier.

Are there dividers in the PLL/VCO CC2538 that could generate these?

Is there a way that coupling from the antenna back into the CC2538 could cause this?

Thanks

Steve R.