Best way to design parallel coupled 12 Ghz filters?

I have a need for designing some narrowband bandpass parallel coupled line filters on alumina. Last time I did this, I optimized them in Eagleware Genesys, and then simulated them in HFSS for a final tweak. They came out without the need to respin them.

I no longer have HFSS available. Rather than just buy or lease HFSS, is there a better filter simulation program out there now? Due to the schedule constraints, I do need to hit these right the first time. It is not good enough if they program is 3% off in frequency, for instance.

In the past I did the
"homegrown synthesis" (my stuff at RFdude.com based on MYJ, and some papers)
-> eagleware -> sonnet.

I always had pretty decent luck with sonnet (and eagleware's EMPOWER if I had time to wait for the simulations).

I wonder though if you will be able to hold 3% across material thickness and Dk variations. I have to admit I only deal with pretty lousy materials with the stuff I work on, but even with decent materials this might be a problem.

Good luck!
Lance