ADM2867E Radiation

Hi, Thomas from Austria- we have a issue with the radiation at 3.77 and 4.02 GHz, violating RX limits of EN 302 571. Until now we could not identfy if it is emitted directly from the chip or via the PCB. We used the reference design from the Datasheet.
the source is clearly the ADM2867E.
Do you have any hints how to improve this behaviour?

Hi, Thomas from Austria- we have a issue with the radiation at 3.77 and 4.02 GHz, violating RX limits of EN 302 571. Until now we could not identfy if it is emitted directly from the chip or via the PCB. We used the reference design from the Datasheet.
the source is clearly the ADM2867E.
Do you have any hints how to improve this behaviour?

Hi Thomas,

Could you share more details on the emission levels you are seeing with the device? I am surprised to see the 4.02GHz frequency appear from the ADM2867E. 

If possible I would recommend reducing the size of the GND2 plane -> This will reduce the antenna area and form a less efficient dipole antenna. If this is not possible and you need a large secondary side ground plane, inductive/ferrite filter can be used to separate an small GND2 plane of the ADM2867E from the rest of the secondary side ground plane. 

Regards,

Neil 

Hi Neil, thanks for the feedback.

The 4.205 GHz is gone, when Vcc is disconnected. The 3.77 needs Vio and the UART to be down.
the 3.77GHz look like this (Frequency depends slightly on temperature:

I will send the 4.205 when I get it.

Regards,
Thomas

Regarding GND2- we do not have a plane for GND2, it looks like this:

We will interrupt it with an inductor close to the chip and see if it helps.

Regards,
Thomas

Good Morning,

Current finding: any modification on the GND2 structure has no effect on the emission.

Regards,

Thomas

We still do not have any improvement on this topic.
do the slower Versions (ADM2863) have different characteristics in this regard?

One additional comment, the spurious we measure is about the same as shown above in your measurement. Unfortunately we have to test against the Radio emitting standard in RX mode, which is lower.