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Port Considerations

As described above, in antenna simulations the enclosure boundaries should be a combination of open boundary conditions, symmetry planes, and ground planes. Since lumped ports can be used in the geometry interior, lumped port setup does not require any special considerations in antenna simulation. Wave ports are typically defined on an external system boundary, so you need to take care when feeding an antenna with a wave port. For best results with wave ports, you should either embed your wave port in a ground plane, or use an internal wave port as described here and here. Both options are described as follows.

If the wave port is embedded in a ground plane, the setup is straightforward. The following image shows a simple horn antenna in a ground plane, from “Materials and Attributes”.

Since the wave port is embedded in the ground plane, it does not touch the open boundaries, and consequently it does not interfere with the far field calculation. When applying a wave port on a ground plane (even one that is not flat, as shown here) no further adjustments are required to ensure that wave port placement does not disrupt the far field calculation.

When your wave port is not embedded in a ground plane, you should use an internal wave port. This is illustrated with the following example. The figure shows a coaxial wire feed for an antenna, where the coaxial waveguide feed extends outside the enclosure. All six sides of the box are assigned PML, indicated in blue. The port is assigned to the center conductor, as indicated by the coaxial cable recommendations. This setup is supported, but results will be inaccurate if the antenna has significant radiation in the direction of the port.

The best option for antennas with waveguide feeds is to terminate the waveguide in the geometry interior, as described in Waveports on waveguides and Use case: coax.

By terminating the coax inside the enclosure boundary, you are able to source a waveguide feed without interrupting the open boundary condition and potentially compromising your antenna results.

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