terahertz VCO problems

dear every body
i meet problem following :
i desgin a terahertz VCO at 80 Ghz, but when i do post-layout , the result frequency with no RC is smaller than 80 Ghz so much (it is about 50Ghz) , the result frequency with R+c+cc aslo smaller than 80 Ghz ( it is about 60 Ghz)
please show me . what is my problems .
is it "layout problem" or another kind of problems,...and how can i solve it

thank you !

At such high frequencies, the design would be too sensitive to parasitics. Layout parasitics can easily cause this to happen. It pays to use pessimistic estimated parasitics on the nodes at the schematic design stage

Boy, the definition of Thz keeps on getting dumbed down.
It used to mean 1E12 and up, now everybody's calling it
half-octave down from there and here you are with 80GHz
(over a decade away) trying to bandwagon.

Evidently you have some layout baggage, but I'd say you
need to have better than a 2:1 capability surplus in the
schematic design, at worst temp / supply / process, to
have any hope.

Looking at signal chain test points all down the line, and
comparing view:view, ought to help you find the point(s)
where you're losing gain @ freq (the likely reason for limited
max freq). Then you might look at the extracted view,
pick off parasitic capacitors for likely nodes and see which
of the big ones might be pointing at unfortunate layout
practices (like putting your VCO under a close-in metal
layer, trying to actively drive a well, co-routed antiphase
signals beating each other back, etc.).

I do not see any details on how you design a VCO at 80 GHz. Above ~20 GHz, oscillators can utilize a dielectric or another high-Q resonator, and above ~40 GHz, Gunn diodes are preferred. The resonant and line structure is mostly waveguide. Maybe there are special MMIC designs of VCOs up to 80 GHz, but such devices are so far highly "laboratory" experiments, no commercial devices.

For a good oscillator, use a lower-frequency quality oscillator followed by a multiplier. See "www.spaceklabs.com" for good mm-wave oscillators. Terahertz is a thousand of gigahertz, so with ~80 GHz are quite low in the terahertz range.

thank every body so much
when i do simulation this circuit , i have to measure "pss" , and i do not know what meaning of " beat frequency" , how can i assign this parameter with VCO oscillate at 80Ghz
many thanks in advance

can some one explain to me ,in terahert circuit, why Vip , Vum. Vqp . Vqm has 0 ,180 , 90 , 270 degree in phase , respectively ?