There are two options to source coplanar lines with lumped ports. The first option is to create two explicit ground references. The following figure shows a close-up view of the end of the center trace where there are two rectangles connecting the center trace to the side traces, following the directions in “Lumped Ports”. The new rectangles are outlined in yellow for clarity.
As explained in “Lumped Ports”, these rectangles are lumped port patches. They become explicit ground references when you apply the port attribute to them, as shown:
Now, the lumped port integration paths go between the center trace and the two side conductors. See “Lumped Ports” for details on lumped port integration paths, and the same section for information on viewing the paths.
You can also use a differential lumped port to source coplanar lines, as shown in the following figure.
The resulting integration paths are identical to the paths produced when using explicit ground reference, as shown above.
As with wave ports, the traces may be nonzero or zero thickness. If you use zero thickness conductors in this case, the integration paths will be collocated. This is okay, and the setup is valid and sometimes preferable, depending on the geometry.