Changes

NOTE: Two or more PEC and conductive sheet traces can coexist at the same Z-coordinate. In this case, the Layer Stack-up Settings dialog shows these trace rows stacked up on top of each other between their common top and bottom substrate layers.

Figure 1: The [[Planar Module]]'s PEC and Conductive Sheet Trace dialogs.

To add a new object set, click the arrow symbol on the '''Insert''' button of the dialog and select one of the two options, '''PEC Via Set''' or '''Embedded Dielectric Set''', from the dropdown list. This opens up a new dialog where first you have to set the host layer of the new object set. A dropdown list labeled "'''Host Layer'''" gives a list of all the available finite substrate layers. You can also set the properties of the embedded object set, including its label, color and material properties. Keep in mind that you cannot control the height of embedded objects. Moreover, you cannot assign material properties to PEC via sets, while you can set values for the '''Permittivity'''(e_r) and '''Electric Conductivity'''(s) of embedded dielectric sets. Vacuum is the default material choice. You may use EM.Cube's Material List for this purpose, which can be opened up by clicking the '''Material'''button. Once embedded object sets are added to the Embedded Sets table, you can edit their properties at any time by selecting their row and clicking the '''Edit''' button.

Figure 2: The [[Planar Module]]'s PEC Via Set and Embedded Dielectric Set dialogs.

'''The most important rule of object connections in EM.Cube's [[Planar Module]] is that only objects belonging to the same trace can be connected to one another.''' For example, if two objects reside on the same Z-plane and geometrically have a common edge which you can clearly see in the project workspace, but organizationally they belong to two different metal traces, then the bridge basis functions will not be generated between them, and the simulation engine will see them disconnected. If two objects belong to the same trace and have a common overlap area, EM.Cube first merges the two objects using the "Boolean Union" operation and converts them into a single object for the purpose of meshing. The mesh of "unioned" areas is usually made up of triangular cells. If two objects reside on the same Z-plane and geometrically overlap with each other but organizationally belong to two different trace groups, incongruous, overlapped cells will be generated that will either blow up the linear system or produce completely wrong simulation results.

Figure 1: Two overlapping planar objects and their triangular and hybrid planar meshes.

* Rectangular objects that contain gap source or lumped elements, always have a rectangular mesh around the gap area.

Figure 2: Edge-connected rectangular planar objects and their triangular and hybrid planar meshes.

Keep in mind that EM.Cube’s Planar MoM engine uses a 2.5-D approximation, whereby only vertical volume currents are assumed inside embedded objects. When the height of an embedded object is small (as should typically be under the 2.5-D assumption), one prismatic cell is placed across the object along the Z-axis. Long PEC vias with a very small radius do also satisfy the 2.5-D assumption. In this case, the long via objects are discretized further along the Z direction and generate multiple stacked cells. Several prismatic cells along the Z-axis may increase the simulation time drastically. This is due to the fact that the host layer is effectively subdivided into a number of sub-layers and the stacked cells are treated as stacked vias embedded inside these sub-layers. As a result, the simulation engine needs to compute all the dyadic Green’s functions accounting for the interactions between all such sub-layers.

Figure 1: Mesh of a vertical PEC via connecting two horizontal metallic strips. The shorter via has one prismatic cell along the Z direction, while the longer via is discretized into several stacked cells.

As mentioned earlier, highly incongruous meshes should always be avoided. Sometimes EM.Cube's default mesh may contain very narrow triangular cells due to very small angles between two edges. In some rare cases, extremely small triangular cells may be generated, whose area is a small fraction of the average mesh cell. These cases typically happen at the junctions and other discontinuity regions or at the boundary of highly irregular geometries with extremely fine details. In such cases, increasing or decreasing the mesh density by one or few cells per effective wavelength often resolves that problem and eliminates those defective cells. Nonetheless, EM.Cube's planar mesh generator offers an option to identify the defective triangular cells and either delete them or cure them. By curing we mean removing a narrow triangular cell and merging its two closely spaced nodes to fill the crack left behind.

Figure 1: Deleting or curing defective triangular cells.

Figure 1: Modeling a periodic screen using two different types of unit cell.

Figure 2: The PMC aperture unit cell and its planar mesh.

Figure 3: The PEC cross unit cell and its planar mesh. Notice the cell extensions at the unit cell's boundaries.