From the ADL5373 datasheet page 11 says: "The balun presents high impedance to the output (VOUT); therefore, a matching network may be needed at the output for optimal power transfer". On page 7 I've seen the smith chart of the Vout S22 (Pin 13) from 2300 to 3000 MHz.
To match the output impedance i would need to have the S-Parameters file relative to the RF output, but I haven't find them on the site. Also, the LO input S-Parameters are needed to simulate its behavior.
Can someone send me these files?