anybody have experience in varactor-tuned microstrip ring filter?

Does performance degrades after adding a varactor? Wich topology is good?
There are many topologies, split-ring with 1 varactor. Split to provide bias, and dealing with some modes.
Ring with 2 varactors and lambda/4 line. Looks easier.
But all of them are not very symmetrical, i think here can be some problems. Anybody added varactors on symmetrical places of the ring?