Although there are plenty of free impedance calculators out there, I'm struggling to find one that can solve impedances for a differential pair using coplanar waveguide. Anyone know of any free software that can do that? The only one I was able to find was Si9000 and Si8000m by Polar instruments, but they aren't free.

Reason I'm interested is because I'm trying to route USB 2.0 HS signals on a 2 layer 1.6mm FR4 board and want to see if using coplanar waveguide will make it more practical (i.e. thinner traces).


  • \$\begingroup\$ What calculators have you tried (to save a thousand pointless suggestions)? \$\endgroup\$
    – Andy aka
    Jul 7, 2014 at 9:06
  • \$\begingroup\$ atlc was mentioned in a recent question, however I've never used it myself. \$\endgroup\$
    – The Photon
    Jul 7, 2014 at 16:06
  • \$\begingroup\$ Also the OP's geometry in that question might help you out. \$\endgroup\$
    – The Photon
    Jul 7, 2014 at 16:09
  • \$\begingroup\$ I tried this once :) It is possible but we had trouble because the reference portion of the coplanar waveguide had to be fairly fat compared to the traces so it took away a large section of pins from the chip. I want to say 1/4" maybe? Moving it away to make space defeated the point. Once we found out the true cost difference between a 4 layer board and a 2 layer board at our volumes we convinced mgmt to go with a 4 layer. By the time you factor in all the advantages including an easier time with EMI... It just made more sense. Good luck! \$\endgroup\$ Nov 4, 2014 at 16:02
  • \$\begingroup\$ Oh and we figured out the waveguide by hand based on Wadell's book amazon.com/Transmission-Handbook-Antennas-Propagation-Microwave/… I seem to have taken it home or I'd check the pages for you. \$\endgroup\$ Nov 4, 2014 at 16:04

1 Answer 1


Try TNT or TxLine.

Also note that your best bet may actually be VERY SHORT (few mm) traces, a thinner board or a 4 layer board :-)

  • 1
    \$\begingroup\$ Thanks for your suggestions. Unfortunately, TxLine doesn't do coplanar waveguide for differential traces. I checked out TNT, but couldn't seem to be able to do the same with that either. \$\endgroup\$
    – Amr Bekhit
    Jul 7, 2014 at 9:34

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