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HELP me about the 12G stripline filter,used the RO4003

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assxdf

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hi everyone
i'm working on the KU band filter,12Ghz. The stripline filter confused me for a long time. i designed the filter use the RO4003 in HFSS.
i test it use the via. The result was so bad ,the center frequence shifted to the left about 400M .The top of the curve is not flat so much.Test results and simulation results are quite different.
in my opinion, there are perhaps two reasons :
(1)the RO4003 has two versions of the dielectric constant ,3.38 and 3.55. I used 3.38 ,maybe i should use 3.55 to design. i don't konw which one should i use. does anybody know that? please help me, thx.
(2)the bad test result maybe brought by via. dose any one has the experence of using via in such band ? The frequence is so high, the via maybe bring bad S11 and S21. dose anyone known that, please help me,thx.
 

How are you achieving the stripline? Is it clamped, or are you using a pre-preg layer to make the sandwich?

The 3.38 and 3.55 numbers are very confusing. Rogers does the same thing with 4350 (the flame retardent bearing version of 4003), listing 3.48 and 3.66. The lower value number is what you get when doing a standard IPC test of the dielectric in a clamped stripline fixture. The nature of the test does lead to the lower number than the "real" dielectric constant due to there being an airgap ont he edges of the resonator. The higher number is measured using a parallel sheet resonance method that is much more suitable to design with.

Rogers has a nice white paper they gave sent me when I whined about the confusing numbers which was very helpful. It also pointed to the dielectric being somewhat anisotropic (higher er in X and Y than in Z) which basically left me paranoid...
 

    assxdf

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hello Garbonzo
Thanks a lot for your guidance. i used the prepreg RO4450 3*0.1mm ,and i used the er=3.54, is it right? i'm not sure about that, because i designed the fillter use the laminate RO4003, the er=3.55, the test result was also shifting, i tested the filter this morning , i will upload my test picture and my design document tomorrow. Please help me examine and analysis the problem. Thank you.
 

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