The input impedance of the LO port of the ADL5801 is 50-ohms differential. T2/T4/T7 was populated with 0-ohm resistors to utilize the differential output of the ADF4351.
Based on experimental results, we determined that 50-ohm pull up resistors provided a better broadband match compared to other resistive matching configurations. Please refer to the 'Output Matching' section for ADF4351 datasheet for more information about matching the output port of the ADF4351. As indicated in the circuit note, the mismatch on the LO path will not degrade performance of the mixer. We recommend keeping the length of the traces connecting the mixer and the PLL to be short as possible.