Thank for your reply! I managed to make BFP420 unstable by adding gate open stub (common gate configuration). Although i use H-biasing scheme with 4 resistors now, but Vce is similar to S53MV's VCO. Now i am trying to calculate push-push oscillator. Actually it goes well. But there is one thing that i can't understand: how 180 degree anti-phase operation is obtained. Here is an example of push-push oscillator (it is balanced oscillator, but can be used as push-push).
http://www.taconic-add.com/en/pdf/technicalarticles--antiphase_design_for_balanced-oscillators.pdf
and here is radar-detector with some information on common resonator push-push oscillator.
http://www.freepatentsonline.com/5402087.html
the length of said microstrip resonator at each side of said output tap is at least one-quarter the wavelength of the oscillating frequency of the respective one of the said pair of transistors to which it is connected plus a sufficient extra length so as to provide a capacitive impedance at the oscillating frequency of each respective transistor
I can't understand between which points 180 degree phase shift is measured. Don't we added additional length to provide capacitive impedance? It now maybe 190 or 200 deg. But in reality it is not. Somehow virtual ground remains in the center of line. I can't understand why virtual ground will be in the center of the common resonator.
I can't understand how to go from one 5GHz building block to push-push with common resonator.
For example, i calculated required Gsource and some inductance to realize it.
It can be realized by open-stub or (short-stub +180 deg).
Because 10GHz push-push will have virtual ground at center, i must
1) decrease single 5GHz oscillator stub length by 90 deg and put them together. Idea is that single 5GHz oscillator have short located at 90 deg from open stub length.
2) or remove short in short stub and connect two oscillators together
But it seems something is wrong with calculations.
Single oscillator is around 5GHz, but when i connect them using this approach, frequency shifts too significantly (5GHz becomes 4GHz to 6GHz). Harmonic output is good (8-12GHz).
So my current problem is i want make push-push frequency right by calculations, not by tuning.