AWR1843: Full span noise follow the target in chamber

Hi,

HW: Custom AWR1843 board

Please refer to the attached file. Page 1 is "no target in chamber". Page 2 is a corner reflector in chamber.

As you can see, there're noise in page 2 and these noise follow the corner reflector when we change the location of it.

We perform several tests and have the following results:

(1) This noise symptom only happens in high antenna gain. The single TX gain is around 20db, 3TX gain is around 24~25db
If the antenna gain is small, there's no noise. The TI AWR1843 EVM doesn't have this symptom since it only has 3 patches and antenna gain is not high.

(2) If we decrease the Tx power by using Tx backoff, the noise is also decreased

I'm seeking your suggestions where could the be the root cause of these noise?

Full span noise follow the target in Chamber.pdf