Skip to content

Waveguide Output Port Boundary Condition

The waveguide output port boundary condition models the electromagnetic field that leaves the computational domain through an attached waveguide. As for the Waveguide Input Port Boundary Condition, the waveguide output boundary condition assumes that the radiation that leaves the computational domain is a well-established waveguide mode. This mode has the propagation constant \(\beta\). The equation for the complex amplitude \(\tilde{\mathbf{E}}\) of the electric field at the boundary of the waveguide output port is

\[ \hat{\mathbf{n}} \times \left(\frac{1}{\mu} \nabla \times \tilde{\mathbf{E}}\right) = j\frac{\beta}{\mu} \hat{\mathbf{n}} \times \left( \tilde{\mathbf{E}} \times \hat{\mathbf{n}} \right), \]

where \(\hat{\mathbf{n}}\) is the unit vector normal to the boundary and \(\mu\) is the magnetic permeability. For an anisotropic material, mufem replaces \(1/\mu\) with the reluctivity tensor \(\nu = \mu^{-1}\). mufem computes \(\beta\) from the same port eigenvalue problem as for the Waveguide Input Port. The same rules apply for the port boundaries, conductors that go through the port, and anisotropic materials.

To create a WaveguideOutputPortCondition, give a name and the boundary Marker:

condition = WaveguideOutputPortCondition(
    name = "My Waveguide Output Port Condition",
    marker = my_marker,
)

Optionally, you can select the outgoing waveguide mode with the mode_index parameter (default 0, the fundamental mode). The boundary term uses the propagation constant \(\beta\) of this mode. Thus, the port absorbs this mode without reflection, but other modes can partly reflect. Use the same mode index as the mode that the input port launches:

condition = WaveguideOutputPortCondition(
    name = "My Waveguide Output Port Condition",
    marker = my_marker,
    mode_index = 1,
)

Usage Examples