I was figuring that if you made a really tight meander delay trace, charge would prefer to jump between the loops, rather than go the long way around. That would make a precursor on a voltage step, and raise the impedance. So one of my guys tried it.
That last meander is about an inch of total length. PADS does that on demand.
The TDR and TDT (reflected and transmitted step responses) are:
In my defense, there is a tiny precursor on the through-pulse, and the impedance changes a little. But not enough to declare victory.
The total one-way delay is about 1.5 ns, and the output risetime is
100 ps. You can clearly see the launch SMA connector (big capacitive spike at 3.5 cm, the three vias, the meander from 7 to 9, and finally the 50 ohms of the second scope channel.The meander trace is 16 mils wide, 22 mils pitch, and it has is 9 mils of FR4 above a ground plane. Total length between connectors is 9".
So, tight meanders seem to work.