How i can properly terminate the pins which oscillates at the frequency fo/2 so that unwanted spurs will not occur?
The fundamental feedthrough (or 1/2 harmonic) that you see is on the RFout port is due to the topology of the device. If you don't need the RFout / 2 port (fundamental freq) simply install an appropriately sized capacitor for the frequency you're working with and a shunt 50 ohm resistor. Otherwise, filtering is the only means of suppressing it.
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