Thanks borich_03 for the suggestion.
I have read the e-book you suggest.
But it seems doesn't solve my problem. I am designing a combline (coax cavity) lossy bandpass filter and has difficulty to achieve the resonance at centre frequency (2 GHz - with very narrowbandwidth i.e 2.5MHz). I have tried to vary the resonator's length, capacitive loading, cavity height, but it responded at only about below 1.6GHz and above 2.4GHz. I dont know how it couldn't go for 2GHz.
Some people says this is maybe due to poor meshing. Then I have changed the lambda refinement from 0.3333 (default) to 0.02. However, it doesn't help much but longer analysing time.
could someone know what exactly is happening? Any suggestion is highly appreciated.
Thks
zaril