we have incorporated in a tranceiver design of ours the hmc821lp6 PLL&VCO part.
We have not noticed any systematic issues with that part in the product mass production phase, so far .
However , recently 3 units have returned from one of our customers experiencing a PLL LD issue for temps >=aproax 40C.
PLL alm is real. When temp increases synth gets unlocked due to a VCo failure .
Please also note that during the issue's occurance , there is no signal at RF output even at a large frequency span.
At a specific temperature range (temp > 40C) and while VCO is still alive, VCO output spectrum is full of non harmonic related spurs .
It seems that VCO malfunctions when temp increases for those parts.
I would appreciate your feedback on that issue.