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Why can I detect a large RFout/2 signal from RFout port, whose power isn't negligible

Dear all,

I used ADF4113HV and HMC738/HMC739 to form an RF sensor.

A very large RFout/2 signal can be detected from RFout port.

Although I used 50 ohm impedance to absorb RFout/2 output.

Some details are shown in the photos.

The substrate is FR-4, and the ground is complete.

The relative power of RFout to RFout/2 is around 17 dB.

The thru-holes were added densely.

Is it possible to use a filter to exclude RFout/2 signal? Or the chip malfunctions itself?

P.S. I hope a enable pin could be adopted to shutdown the unused port.

Thank you.

Spectrum analyzer output

RF connection