As explained in the lumped port section, lumped ports introduce parasitics to the system, but they are faster than wave ports and may be used in the system interior as well as on the exterior. When using a lumped port to source a coaxial cable, the most straightforward technique is to apply the port attribute to the core conductor and the dielectric, as shown. The port index label only appears once in this image because it overlaps for the two applications.
The coaxial structure in the above figure has a port applied to both the inner conductor and the dielectric. The next figure shows a lumped port mesh annotation, so you can see the integration paths that radiate from the center conductor to the shield.
With a lumped port, we also support the case where the core and shield are not coplanar. Use a differential port to achieve this. In this case you must use a finite-thickness outer conductor, because you cannot apply a lumped port to a curved zero-thickness conductor.
The following image shows the integration paths for a geometry where the core is longer than the shield.