One technique to improve the phase noise in wide-band VCO's was shown by
Ulrich Rhode. He uses several diodes in parallel in order to decrease the
RF
current in each diode, reportedly lowering losses and improving noise. I
never tried it myself.

If the diodes are the limiting factor, it can help.
The second diode seemed to do the most good,
the third, a little more, but any more didn't help
(in my designs).

The way the varactor is made will affect the
noise performance. Ask the manufacturers
which process yields their best phase-noise
performance. Most of them are very helpful.
As I recall, planar, epitaxial construction,
with thermal compression bonded leads
gave my best results. Hyperabrupt diodes
gave the worst. But things change rapidly
these days, so ask.

73, John - K6QQ