Chris Bartram G4DGU
I've just been deleting some old posts and I noticed your comment about PCB materials. I think you are being a little hard on the reputable PCB manufacturers! Most of the good ones - both those who make specialist microwave laminates, and many of those who produce lower cost materials, do have good data on the dispersive change of Er with frequency, as this now needs to be taken account of in the design of fairly ordinary PCBs. Some modern laminates, such as FR408, now have surprisingly stable and reproducible, Er figures up to 10GHz and even beyond! Losses are not that much improved though - but with care they are acceptable for much work for <=10GHz.
Of course, anyone using stock FR4 is at the mercy of low cost manufacture, but even there, I've been able to a good job in the 10GHz region - although printed filters are out, unless ... :-) Watch this space when I get a bit more time!
Luxulyan, Bodmin, Cornwall