Negative Resistance In Microwave RIng resonators

[sshz44]

Hi,
Iam Currently working on My MSc Thesis and i have to design a negative resitance circuit to be coupled in to a Microwave ring resonator , to compensate for the losses in the ring, i have tried a lot of things but i wasnt able to get desired results, any help in this regard would be really a favour to me, as i have to submit my thesis by the end of this month. the centre frequency is 6 Ghz, i have used Microstrip tarnsmission lines, all r ditributed elements.
Thanks

 

[biff44]

Well, I always just think of the resonator/active device as a pair of microwave black boxes with S parameters. If the reflection coefficient of the ring resonator is 0.6, for instance, I know that if I hook up an active device with a reflection coefficient of 1.7 and the right phase angle, it has a chance of oscillating. Set up your feedback on the active device to be 20% higher than that value, and it will probably start up in the real world.