I have found an issue when measuring the conversion power gain and P1dB of ADL5380 that I have designed with a 3GHz LO system. (LO level is 2dBm)
when RF is 3.125GHz (-6~3dBm sinewave signal),
I& Q baseband output with a smaller power level compared with the level when RF is 2.875GHz. (1 to 2dB).
RF (3.125GHz)= 3dBm. LO=3GHz I&Q Pout=-0.4dBm,
RF (2.875GHz)= 3dBm. LO=3GHz I&Q Pout=-1.5dBm,
I have also measured the ADL5380 EVB under the same condition, they're balanced and have the same output power level. RF in= 0dBm, I& Q baseband pout=-6.5~6.7dBm
Attached is my schematic. Could you review and advise what could possibly be the root cause?