The attached circuit recommended as an Interface Shematic for Vcc shown in the data sheet is a must?
I don't understand much about a role of this circuit and if possible, I would not like to use it due to PCB space issue.
The circuit you're referencing is inside the HMC385LP4. The evaluation board circuit (see pg 11-18 of the datasheet) which consists of a couple of power supply de-coupling caps will be fine if you have a clean regulated supply for Vcc.
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