[[Image:image121.png|thumb|400px|Diagram of an equilateral triangular periodic lattice.]]
[[Image:image122.png|thumb|600px400px|Modeling a periodic screen using two different types of unit cell.]][[Image:pmom_per5_tn.png|thumb|400px300px|The PEC cross unit cell.]]
[[Image:pmom_per6_tn.png|thumb|400px|Planar mesh of the PEC cross unit cell. Note the cell extensions at the unit cell's boundaries.]]
=== Infinite Periodic Structures & the Periodic Lattice ===