I'm routing a U.FL connector to a cellular module (Telit GE864).

According to this calculator a 1mm track with 0.16mm gaps should provide a 52Ω impedance path to an U.FL antenna connector.

A Sparkfun breakout board for a similar module uses an open space (~1 cm high) with a far wider trace (2.8mm). Both traces are approximately 6mm long.


Coplanar waveguide


Open space

Which of these connections is preferable?

  • \$\begingroup\$ Sparkfun's looks like an attempt to make a 50 ohm microstrip on a two layer board. Maybe try to calculate that and see if it is. Just a guess but it doesn't look like a coplanar waveguide to me. \$\endgroup\$ Apr 14, 2015 at 13:38
  • \$\begingroup\$ Try entering the sparkfun dimensions into the calculator and I bet you get similar results. Tip - use 1.6mm board thickness. \$\endgroup\$
    – Andy aka
    Apr 14, 2015 at 13:45
  • \$\begingroup\$ Yes, running the sparkfun board properties through a calculator results in 2.8mm trace width. What are the pros/cons of each solution? \$\endgroup\$
    – Lg102
    Apr 14, 2015 at 13:50

1 Answer 1


Like the comments say, the Sparkfun layout is a microstrip layout. Microstrip is a waveguide where the return path is on the ground plane beneath the signal path. Whereas coplanar waveguide is a waveguide where the return path is (predominately) on copper regions in the same plane as (coplanar with) the signal conductor.

I think your design is better than Sparkfun's.

The benefit of coplanar waveguide in this design is that it allows a narrower trace which matches the pad dimensions better and doesn't need a neck-down before readhing the antenna pad.

In other situations, microstrip might be preferred because a wider trace will have lower resistive loss, or because it's impractical to maintain symmetric ground regions on both sides of the signal trace.


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