This example of a balanced antipodal Vivaldi antenna demonstrates the CAD import capabilities of XFdtd. The geometry was initially constructed in AutoCAD and then imported into XFdtd using the 3D Solid CAD Importation Module. The antenna is comprised of three layers where the outer ground plane layers are flaired in the opposite direction of the Vivaldi. The full structure is shown in SAT format in Figure 1 while Figure 2 and Figure 3 show the metal layers (Vivaldi layer shown in yellow) as both solids and wire frames (wireframe view from AutoCAD). The thickness of the layers is exaggerated in the figures for clarity. The substrate of the antenna is 40x90x3.15mm and is constructed of a duroid material with a relative permittivity of 2.32.

The XFdtd antenna is simulated using 1mmx1mmx0.7875mm cells (Z dimension modified to match the 3.15mm thickness) in a space of 100x65x165 cells (Figure 4 - center conductor, Figure 5 - one of two outer conductor layers, Figure 6 - three-dimensional view). Two projects are created to simulate the antenna with a broadband pulse and a 10GHz sine wave. The feed is applied in line with the center conductor at the base of the stripline as shown in Figure 4. The source resistance at the feed is set to 43 ohms to best match the input impedance of the antenna. The simulation is run for 2000 timesteps which requires approximately 15 minutes on a dual 700MHz Pentium III computer using the Remcom multiprocessor processor module. Less than 35 MB of RAM are needed for the job.

The S11 versus frequency response is shown in rectangular plot format in Figure 7 and in Smith chart format in Figure 8. The gain patterns in the two principal planes are shown in Figure 9, Figure 10, Figure 11, and Figure 12 in both rectangular and polar format. The coordinate system is referenced with Theta=0 at the flaired end of the antenna or up in Figure 4 and phi=0 to the right in Figure 4.

An animation of the time-progression of the transient current magnitude of the 10GHz sinusoidal source is shown in a three-dimensional view in Figure 13. Figure 14 and Figure 15 show the conduction current magnitudes in the planes of the center conductor and one of the outer conductors.