What is the purpose of the unbalanced resistor T-network on the evaluation board for RFIN pin 3?
If it's an impedance converter, what the target output impedance and attenuation?
The resistive T-network is for wideband impedance matching of the RFIN. The network also helps to improve the input return loss of the HMC713LP3E-EVALZ eval board. Data sheet page 11-4 shows the Input Return Loss graph. It is about -10dB or better to the wide frequency range. The network has about 6dB insertion loss.