Changes

[[Image:fdtd_lec1_23_3dtotal.png|center]]

Besides 3D visualization of the radiation patterns, you can plot 2D graphs of the patterns at certain plane cuts. The 2D radiation patterns can be plotted as both Cartesian and polar graphs. Open up the Data Manager dialog and spot Cartesian pattern data files with a “.DAT” file extension as well as the polar (angular) data fileswith a “.ANG” file extension. The figure below shows the Cartesian and polar radiation pattern plots in the YZplane cut. Besides the three principal XY, YZ and ZX plane cuts, there are also data files for one additional userdefined Phi‐plane cut, which by default is calculated at φ φ = 45°45^o.

[[Image:fdtd_lec1_To examine the port characteristics of the dipole antenna, open up the Data Manager again.png|500px]]The S/Z/Y[[Image:fdtd_lec1_parameters are written into complex data files with a “.png|500px]]CPX” file extension. To graph the S11 and Z11[[Image:fdtd_lec1_parameters, select the files “DP_S11.CPX” and “DP_Z11.CPX”. You can view the contents of the two files using the <b>View</b> button of Data Manager. To plot them in EM.Grid, click the <b>Plot</b> button of the dialog. By default, the S parameters are plotted on magnitude/phase Cartesian graphs, while the Z and Y parameters are plotted on real/imaginary Cartesian graphs.png|500px]]  [[Image:fdtd_lec1_fdtd_lec1_26_syparameter.png|500pxcenter|S and Y parameter.]]  From the above graphs, it appears that the resonance occurs somewhere around 900MHz. This is thefrequency at which the imaginary part of the Z11 parameter (input reactance) crosses zero. But, how does that make sense? There are several reasons to justify this result. First, a resonant dipole is not exactly half‐wave, and its resonant length is usually slightly less than &lambda₀/2. Second, the input impedance of a dipole antenna is a function of the wire radius. In this FDTD simulation, you did not model the wire thickness. In other words, you assumed that the dipole has a “zero radius”. Third, the lumped source is connected between two adjacent mesh nodes. Therefore, its field strength depends on the mesh density. If you increase the mesh density to 30 or 40 Cells/&lambda_eff, you will observe that resonant frequency of the dipole antenna will change and get closer to 1GHz.