X band VCO with reverse bias of GaAs Fet

Looking to the layout of an X band VCO (tuning range 9.2GHz--9.5GHz) I have seen that the GaAs Fet was polarized in reverse mode. The +5Vdc power supply voltage was directly connected to the source terminal through a choke microstrip circuit. Along the Drain output line (rf output of VCO) a 82ohm resistor was series connected ( It acts like an attenuator I suppose) with a proper dc path to ground. The Gate line was connected to a varactor circuit and in the choked dc path was connected a 10K resistor toward the ground. Each of two Source terminal were also connected to an open stub (Approximately 1/4λ or little more) ....uhmmmm?
Also I have noticed that this type of oscillator has a better spectral purity than a similar vco with the usual positive bias on the Drain.
I think that the spectral purity improvement depends on this particolar type of bias adopted for the GaAs Fet.
Someone of you can kindly give some technical explanation to me.
Thanks in advance

Do you have more infomration about your design ?

this may help