[SI-LIST] Attaching coax cable to board

 
Suppose you attach 50ohm cables from a synthesiser to you board through SMA . 
Its 10G differential setup. The board contains a microstrip/coplanar waveguide 
connecting the SMA to your IC which has 50ohm termination connected to Vcc

It seems to me you have field lines in the coax between the center conductor 
and the sheathing. This then somehow has to transfer to fields between the 
differential microstrip/coplanar wg on your board. The field lines between the 
surface line and the ground provides the common mode impedence whereas the 
field lines between the conductors provides the differential mode Z.

Now my question is: should you connect your SMA ground to the IC ground or 
should you keep it isolated. If you keep it isolated, should you connect 
decoupling caps between your IC ground (ie the board ground) and the SMA ground.

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