Changes

EM.Cube's periodic FDTD simulator uses periodic boundary conditions (PBC) to model an infinite periodic array. All the periodic replicas of the unit cell structure are excited. In this case, you can impose a phase progression across the infinite array to steer its beam. You can do this from the property dialog of the lumped source or waveguide source. At the bottom of the '''Lumped Source Dialog''' or '''Waveguide Source Dialog''', there is a section titled '''Periodic Beam Scan Angles'''. This section is grayed out when the project structure is not periodic. You can enter desired beam scan angle values for both '''Theta''' and '''Phi''' in degrees. At the end of the periodic FDTD simulation, the radiation pattern of the unit cell is calculated and stored in a radiation data file with a '''.RAD''' file extension. The 3D radiation patterns that you normally visualize in EM.Cube, in this case, correspond to the single unit cell, not the infinite array. Therefore, they do not show the beam scanning even if you have entered nonzero values for the &theta; and/or &phi; scan angles. For this purpose, you have to define a finite-sized array factor. You do this in the "Impose Array Factor" section of the '''Radiation Pattern Dialog'''. In the case of a periodic structure, when you define a new far field item in the Navigation Tree, the values of element spacing along the X and Y directions are automatically set equal to the values of the periodic lattice spacing along those directions. Set the number of elements along the X and Y directions to any desired values. EM.Cube will then compute the radiation pattern of the specified finite-sized periodic array, and the beam scanning will appear in the radiation pattern plots, if any. <font color="red"><u>'''Note that for large &theta; scan angles, the periodic FDTD time matching loop may take far more time steps to converge.'''</u></font>

Figure 1: (Left) Setting periodic scan angles in the lumped source dialog, and (Right) Setting the array factor in radiation pattern dialog.

Figure 2: Radiation pattern of a 8×8 finite-sized periodic dipole array with scan angles: (Left) &theta; = &phi; = 0°, and (Right) &theta;= 45° and &phi; = 0°.