As Scott said, option 2 is a good choice.
However if you are using a 3D EM tool such HFSS or EmPro etc. You can use
the port solver benefits.
For instance the waveport in HFSS solves the 2D fields for the cross
section seen at the port and computes the main parameters of the
transmission line seen at that port.
This means that the port is automatically terminated to its characteristic
impedance in the whole frequency band... And this give to you the perfect
termination, no reflection due to fixed reference impedance.
At the end the S-parameter matrix can be renormalized to 50 ohm.
Just pay attention that this such port is not too electrically close to
your discontinuity, if so extend the cross section and than de-embedd at
the interested reference plane
Hope this help
Regards
Cristian
On Thu, Aug 20, 2015, 6:08 PM jun zhang <zhangjun5960@xxxxxxxxx> wrote:
Hi Experts,
When I do SMA launch optimization, my SMA has characteristic impedance
50ohm, but the trace connected to the SMA has impedance 42.5ohm.
In such a case, when I do the launch optimzation about antipad, GND vias,
do you think it's better to compare S parameters with 50ohms on both ends
or that with 50ohm at SMA end and 42.5ohm at the trace end?
--
best wishes,
Jun Zhang
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