FreeLists / si-list / [SI-LIST] Re: Effective dielectric constant

[Ed Sayre III <esayre3@xxxxxxxx>]

Atif,
    Unfortunately,  Wadell's formula assumes a uniform dielectric, and you 
clearly do not have this.  Much of the problem lies in the trace width, 
height, and spacings relative to the dielectric thicknesses.   I would 
suggest you check out  K.C. Gupta's book "Microstrip Lines and Slotlines" 
chapter 7 to get a better understanding of the problem.

         Good luck
         -Ed Sayre


At 03:48 PM 6/2/2003 -0700, you wrote:
>Hi
>I am working on SOI(silicon on insultor) with silicon (Epsilon r = 11.9 
>and h= 550 micron)and then on  top of this is Sio2 (Epsilon r = 4 and h= 8 
>micron).Then is the metal layer(copper) .A part of the metal structure is 
>coplanar strips and I am trying to find out the charactersitic impedance 
>of the cps.For that I need to know the effective dielectric constant .I am 
>using the equations from waddell 's design handbook.Confusion is which 
>Epsilon r to be used in the equations..(11.9 or 4 ) Also for "h" do I just 
>use 558 micron(by simply adding both the heights) and why? appreciate all 
>the info regarding this..
>Thanks
>Atif
>
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