HMC778 RFOUT coupling cap (why 100 pF)?

Hello ADI,

Why was a 100 pF coupling cap used on the HMC778 RFOUT on the eval board schematic?  Since this part operates around 10 GHz I would have expected that a much smaller coupling cap would be used.  I swept a 100 pF, C0G 0402 cap at 10 GHz and the insertion loss = 0.6 dB and the return loss = 13.5 dB.  Does ADI want the coupling cap to work down below 1 GHz for some reason?



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