HMC659LC5 RFIN DC block cap ?

The application circuit does need an external dc-blocking capacitor but this capacitor was left off of the eval board to afford maximum evaluation flexibility. So for folks who want to go down to a very low frequency, they can use a large cap but that my cost them bandwidth at the top end of the frequency range. For bench evaluation with the evaluation board, I would suggest that you get a coaxial dc block.