Fet oscillator design: what if replace gate microstrip stub with microstrip ring?

[Terminator3]

Did anybody here tried that? Instead of coupling microstrip ring or DRO to gate stub, we connect microstrip ring directly to gate. Even varactor can put in there.

Any problems with that design?

I am interested in such design because:
1) we can put transistor inside the ring -> miniaturisation
2) drain output goes through via or simply coupled to microstrip line on the other side of dielectric.

also have a feeling, that it can give more power output.

 

[biff44]

where u place the active device is somewhat irrelevant. But you may not want to "directly" attach a gate to a microstrip ring, as you would end up with a very low Q resonator. There is decoupling inherently built in, either with a small value lumped capacitor or a physical gap between the ring and the gate stub. With the proper decoupling, your loaded Q will be much higher, and the oscillator will behave better (lower phase noise, less timing jitter, etc)

Placing a device, and its bias circuitry, inside of a resonant ring will likely shift the resonant frequency. It may even cause multiple resonances (due to added parasitics) which could, in the worst case, make the oscillator work at more than one frequency at a time.

 

[Terminator3]

Thank you. One more question. What if i still connect ring to gate without gaps or capacitors, can it improve output power at the price of higher noise?

 

[Terminator3]

Please help with design procedures for microstrip ring resonator.
I make this picture above to make my question more obvious: I want eliminate microstrip stub and make resonator as shown on the right part of picture: If L2 is eliminated, then gap between ring and L3 can be represented by capacitor, so the left scheme becomes the same as right. My question is do we need L4 stub before ring and why? Only for optimizing reflections for oscillation? Can we throw away this nasty L4 and what happens?

Left part of picture: length of source stub L1 for certain frequency producing "inductive" stub to increase instability. How L2 and L3 must be analyzed, the same way as DRO?

To conclude: i want to know design procedure for L4 stub length, wich connects microstrip ring and gate of FET through capacitor C. Is there any way to replace ring part with simple straight microstrip to use standard design procedure? Ring is 360deg for frequency F (only first harmonic).

 

[Terminator3]

I still have problem. I want to use analytical formulas, as with DRO. For DRO, there is equivalent scheme, where real numbers can be put in formulas and analyzed.
For DRO: check stability factor, match gate and drain and calculate distance to DRO

For RING attached to gate: check stability factor, match gate and drain. I can't understand how i must do this matching?

My current guess: look at FET as stand-alone microstrip oscillator with series feedback, calculate gate and drain stubs (maybe additional source stub). Then put ring at the end of drain stub, not on side, directly on axis, because i do not need DRO "emulation".

Guess #2: assume ring is equivalent to 180deg stub (although ring length is 360 deg). Then substract 180 deg from gate stub length, calculated for series feedback. Then gate will be attached to L-180deg stub, sutb attached to ring through capacitor.

i can't understand how to look at that ring: as a part of gate stub, or separate element with only some coupling.

 

[Terminator3]

I realized some new things! Hope somebody can give comments if it is correct:

1) to make microstrip oscillator, we choosing reflection coefficient Гs close to the inverse of S11. Then finding impedance Zs from Гs and microstrip length L from Zs.
2) if we go from S11 directly through line L, impedance transformed to the open-circuit. So it looks that transistor with line L of impedance Zs produce half-wavelenght open-circuited resonator. Some part of this resonator is "inside" transistor S11, and the outer part is line with length L.

Using this idea, i try to attach ring resonator. It seems that it is enough just put that resonator after L of (Zs), because ring resonator transforms impedance by half-wavelenht, and we again at open-circuited point on smith chart.

 

[Bob60]

These staff is quite tricking. S11 that is low signal parameter, strongly saying they not valid for oscillators.
Below is probably my design of the DRO + PLL oscillator. It is staff not for professors, otherwise appear questions, what is it? love or science and why student can and professor not.