Re: grounded co-planar waveguide PCB design advice please


"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> a écrit dans le
message de news:ehh312ltkmicboadjnamh1vclo4frj73eh@xxxxxxxxxx
On 10 Mar 2006 04:53:24 -0800, "megoodsen" <hq105862@xxxxxxxxxxx>
wrote:

Hi,

I'm designing an RF multilayer board that is to work over 10-200MHz.

For the transmission line I'm using grounded co-planar waveguide.

Material is 10 thou Rogers 4350B, with a 50ohm track width of 0.46mm
and a track to top ground gap of 0.146mm.
This is working OK.

I now want to shield the board to prevent crosstalk, but I am
restricted to very little height.

My plan is to get a flat plate of say 1mm material half mm deep etched
with pockets that follow the RF lines and is grounded all elsewhere.

My worry is, will the fairly close proximity (but nearly 4 times the
track to gnd distance) of the metal plate above the transmission lines
cause problems, and/or will I have resonating cavities too?
I can make the cavities be 3 or 4 times wider that the gnd to gnd gap
around the lines if need be.

What do you think?

73

This will seriously change the impedance, so you'd have to narrow the
trace if Z matters. And the mixed dielectrics (epoxy-glass and air)
will make the calculations a real pain.


I don't know for a coplanar line, but with a microstrip line, just compute
the impedance with any calculator for a buried line, then multiply the air
side thickness by Er and you'll have the corresponding air thickness,
provided the sidewalls are not too near the line.

Also, why using Rogers4350 at 200MHz? Unless you need it for some other part
of the design, this is overkill.


--
Thanks,
Fred.


.

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