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Best Practices for Efficient and Effective Planar EM Simulation 15 www.cadence.com/go/awr Best Practice Tip #6: Understand the issues regarding thick versus infinitely-thin metal. The mesh count is lower for non-zero thickness metal, but accuracy can be affected. The EM planar layout environment works with polygons on a STACKUP of material layers. The polygons can have thickness, which in the AWR AXIEM simulator is typically used for signal lines, where the non-zero thickness of the metal can be important for accurate simulation. Non-zero-line thickness should only be used where needed as it will lead to a larger mesh, which in turn will cause a longer solve time and larger memory usage. The thickness of the line is set in AWR Microwave Office software by drawing the polygon on a drawing layer, which is then mapped to the STACKUP using the EM mapping table. (This has been covered already in Best Practice Tip #2). The mapping table includes a Material column, in which a keyword sets the thickness of the polygon and the bulk material of which it is made. The AWR AXIEM simulator can only use conducting materials, although the AWR Analyst simulator can also use dielec- trics, for example for a ceramic resonator. The polygon can either be extruded upward or downward by giving a positive or negative thickness and the extruded polygon will embed itself into the layer above or below it. Note that dielectric layers for extruded shapes do not "grow" in AWR AXIEM software. For example, a 10mm PCB layer will stay at 10mm thick, even if 0.7mm thick lines are embedded in it. Therefore, above the lines, there will be 9.3mm of Teflon, not the original 10mm. The designer can see if the AWR AXIEM software will simulate the lines with non-zero thickness by looking at the 3D view of the geometry; the Preview Geometry option will also show if the lines have thickness. The 3D view is already using the EM layer mapping table, so the thickness will be applied. Figure 16 shows a microstrip line on a PCB where the thickness has been set to 0.7mm. The upper left picture of the 3D view shows the line has thickness. Figure 16: Microstrip line and 3D view with thickness (top left), thick metal line with edge meshing and 204 unknowns (bottom left), and thin metal line with edge meshing with 57 unknowns (top right)

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