This example demonstrates a complex antenna comprised of a composite right/left-handed (CRLH) waveguide and unequally spaced slots [1]. The antenna is fed by a WR-90 waveguide that enters at the bottom of the device. After the input port, a matching transition region modifies the fields for propagation down the CRLH waveguide. The CRLH waveguide has numerous equally-spaced unit cells which each contain small apertures for field propagation. The radiation is through six tilted slots in the top plate of the waveguide. The spacing between the slots and the tilt angle of each slot varies.
The CAD-based geometry in XFdtd is shown in Figure 1 where the input port is to the left and bottom and the CRLH waveguide extends to the right. The slots are visible in the top of the structure of Figure 1. A more detailed view of the slots is shown in Figure 2, where the XFdtd mesh is also visible. Due to the complex nature of the slots which are not aligned with the FDTD grid, the XACT Accurate Cell Technology meshing feature is used to precisely mesh the slot dimensions and orientation. In Figure 3, the input port at the bottom of the waveguide is shown with the applied TE10 mode. A cut-away mesh view of the interior of the waveguide is shown in Figure 4.
Figure 1: CAD view of the geometry constructed in XFdtd showing the CRLH waveguide and the radiating slots.
Figure 2: Detailed view of the XACT-meshed rotated slots of the device.
Figure 3: Bottom view of the device showing the input port with the waveguide excitation.
Figure 4: Cross-sectional mesh view of the device showing the interior CRLH cells.
The geometry is meshed with large boundaries surrounding the structure for better display of color field images. As meshed, the geometry requires about 268 MB of memory to simulate and runs in slightly more than 6 minutes on an NVIDIA C1060 Tesla GPU card.
Of primary interest in this example is the resulting radiation pattern from the device. The three-dimensional gain pattern from the antenna at the center frequency of 10 GHz is shown in Figure 5 with the device at the center of the pattern. The gain in H- and E-planes is shown in Figures 6 and 7. The conduction currents along the top plate of the antenna are shown in Figure 8. In Figure 9 the transient electric field radiating out of the waveguide is shown at an instance in time.
Figure 5: The three-dimensional radiation pattern of the antenna at 10 GHz.
Figure 6: The H-plane radiation pattern at 10 GHz.
Figure 7: The E-plane radiation pattern at 10 GHz.
Figure 8: Vector display of the conduction currents on the top of the waveguide at 10GHz.
Figure 9: Image of the transient electric field in a cross-section of the device.
References
S. Liao, J. Wang, Y. Chen, W. Tang, J. Wei, J. Xu, and Z. Zhao, "Synthesis, Simulation and Experiment of Unequally Spaced Resonant Slotted-Waveguide Antenna Arrays Based on the Infinite Wavelength Propagation Property of Composite Right/Left-Handed Waveguide,” IEEE Trans. Antenna Propag., Vol. 60, July 2012, pp. 3182-3194.