Hi Krishnan

Per your mail it seems like an antenna fed by a
differential pair.  If it is a differential pair,
signal will go through one of them and return current
will come back through the other.  Thus when TDR gives
true differential signals, ground plane is not needed
for differential impedance measurement.  However, as I
know there are some brands of TDR do not give true
differential signals when measuring differential
impedance.  For this kind of TDR, ground plane is
needed or you will not get differential impedance.

Best Regards,
cyjui


--- Balasubramanian Krishnan
<[log in to unmask]> 說：

> Dear All,
>       For an 13.56 MHz antenna trace (25 mil wide &
> 400 mm long) running
> between 2 pins of a differential transceiver (Tx1 &
> Tx2) we want to
> maintain dimensional tolerance of + / - 10 % (trace
> width & trace thickness
> including masking)? What has to be specified in the
> fabrication notes for
> this?
>       There is no reference plane below this trace.
> How to ensure the
> impedance tolerance is within 10 %? How should be
> the impedance coupon
> designed for this purpose to do TDR measurements?
>
> Sincerely
>
> K.Balasubramanian
> Project Leader - Hardware.
>
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