Where To Find This Example
AWR Version 13
AWR Version 12
This project demonstrates the simulation of an 8x8 Butler Matrix using AXIEM. Note that this simulation contains over 30K unknows, and may take over 30 min per frequency on a reasonably fast computer with multiple processors.
The Butler Matrix is often utilized as part of the Beam Forming Network for a phased array. It serves to provide the necessary phase and power division necessary to the antenna elements for beam steering, depending on which input port of the matrix is selected.
The 8x8 Butler Matrix design presented in this example is centered at 10 GHz. The output section consists of one wavelength long lines, so that the phase shift between the output ports can be viewed by plotting the currents along those lines, and looking at the peaks and nulls of the current waveform.
Two EM Structures are included in this project. The first, "Butler_Matrix_8x8" is setup for simulation from 8-12 GHz, and all of the graphs refer to this project. The second structure is "Bulter_Matrix_8x8_10GHz_currents". It setup for simulation at 10 GHz only.
The Butler Matrix is implemented on a double-sided board with an internal ground plane. As a result both the Top and Bottom Boundary is set to "Approx Open" on the Dielectrics Tab in the Enclosure Properties window. In order to reference the ports to the internal ground plane, all the ports are set "Connect to lower" for the Explicit Ground Reference in the Port Attributes window.
Both EM Structures utilize Geometry Simplification Rules to simplify the mesh, written on the "Rules" tab of the enclosure of the structure. Refer to the AWRDE Simulation and Analysis Guide for more details on geometry simplification. The most notable effect is the conversion of circular vias to squares when viewing the mesh.
Viewing the Currents
The EM Structure "Butler_Matrix_8x8_10GHz_currents" has been set up to view the currents at 10 GHz. The currents are displayed in the 3D EM Layout. The currents may be turned On or Off by toggling the EM_Current annotation. Animation of the current can be enabled by clicking the Animate Play button on the EM 3D Layout toolbar.