Is a 'soft' pull-down like 250 ohms acceptable for the unpowered VCO supply lines?

If not, why is it that they should be left floating rather than pulled down?

Also, what is the nominal value of the on-chip VCO power bypass caps?

Thank you.

You need a PLL which drives a frequency doubler which drives an amplifier. Possible choices might be ADF4371 (PLL),  HMC1105 (frequency doubler) and HMC7229 (amplifier). These are not the only choices.

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