Re: [SI-LIST] : Coplanar Transmission Line

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From: Ray Anderson (raymonda@radium.eng.sun.com)
Date: Thu Feb 03 2000 - 11:34:49 PST


        I've used them in the past in some 800 MHz IF interconnects
in a satcom application. In this application we fabbed the lines on
a flexible Kapton substrate.

        Coplanar waveguide obviates the need for a ground plane yet
provides a controlled impedance interconnect.

        The ground return path is in the conductors that lay in the
same plane as the signal conductor on either side of it. If I remember
correctly (it has been quite a while), to achieve low impedances
like 50 ohms the spacing between the signal and ground traces needed
to be quit narrow.

        The coplanar lines are quite low in loss as you don't have a
lot of field lines traversing a substrate material.

        Cascade Microtech uses the coplanar waveguide technique in
the fabrication of a lot of their microprobes.

        I probably could remember more about them I if I really thought
about it, but that should get you started. I'm sure others on the list
can supply additional input. Oh yeah, check Bahl & Bhartia :)

-Ray

>
>
>
> Dear SI Experts,
>
> Who out there has worked with coplanar (waveguide-like) transmission lines as
> opposed to stripline/microstripline?
>
> What can you tell me about it other than what I can find in Collins or Bahl &
> Bhartia?
>
>
> Thanks in advance,
>
>
> Roy
>

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