Boundary Conditions - Boundaries

Due to the fact that a computer is only capable of calculating problems that have finite expansion, you need to specify the boundary conditions. This can be done within this dialog box.

When you enter the boundaries property sheet, the modeled structure is displayed with a surrounding bounding box colored with regard to the boundary condition at each boundary. The picture on the right shows an example of such a bounding box.

The assignment of the colors to the boundary conditions is listed together with the description of the different boundary conditions below.

Electric: Operates like a perfect electric conductor: all tangential electric fields and normal magnetic fluxes are set to zero.

Magnetic: Operates like a perfect magnetic conductor:  all tangential magnetic fields and normal electric fluxes are set to zero.

Open (PML): Operates like free space: waves can pass this boundary with minimal reflections. Note that in case of a unit cell simulation with the general purpose frequency domain solver open boundaries are realized by a Floquet port.

Open (add space): Same as Open (PML), but adds some extra space for farfield calculation. This option is recommended for antenna problems.

Periodic: Connects two opposite boundaries with a definable phase shift such that the calculation domain is simulated to be periodically expanded in the corresponding direction. Thus, changing one  boundary to periodic always changes the opposite boundary to periodic as well.

If you select a periodic boundary condition you may enter a phase shift for this boundary in the Phase Shift/Scan Angle property page.

Simulating antenna models with periodic boundaries enables you to examine the near field influence among the individual antennas. However, note that the resulting structure represents an infinitely extended antenna pattern. Hence the farfield results are most accurate in conjunction with the definition of an (preferably large) antenna array in the farfield postprocessing. Please refer to the farfield overview for details.

Conducting Wall: This boundary behaves like a wall of lossy metal material.

Unit Cell: A Unit Cell boundary condition is very similar to the Periodic boundary condition. In addition, a two-dimensional periodicity other than one in the direction of the coordinate axes can be defined (Boundary Conditions - Unit Cell). If there are open boundaries perpendicular to the Unit Cell boundaries, they are realized by Floquet modes, similar to modes of a wave guide port . The farfield considerations are the same as for the periodic boundaries.

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