Radiated Emissions failure (receiver spurious emissions test)

[EclectronicDesign]

We are currently going through certification and have had an interesting failure during radiated emissions.  When in normal transceiver mode, all is well, but when we put the device into a special receiver only mode using the Wirepas tool then we fail at the second harmonic of 4.8GHz even though there are no emissions at 2.4GHz.  Very odd. 

I would have thought that, if anything, we would fail a transmitter test rather than a receiver test.  Could the emissions be coming from the receiver local oscillator?  What would you suggest to try and fix it?

Incidentally, we are using a pretty standard meandering inverted F PCB trace antenna with parallel cap and series inductor. 

[WoutZenso]

Hi Kristin,

We encoutered the same issue (I made a private ticket where I shared my design files). We use the CIAA package and there is no updated reference layout for this one, only for QFAX. The P0.25 and P0.26 are unused in the final product, but by coincidence we used these pins for the UART connection for DTM mode. I was wondering, since we don't use these pins and I would like to find a fix which does not mean another iteration on the PCB, if it is sufficient to ground the pins by setting an internal pull-down? Or is it required to have a direct ground connection?

Best regards,

Wout