Parallel Plate Waveguide

The simplest possible openEMS simulation: a parallel-plate waveguide excited with a sinusoidal TEM mode, demonstrating the core workflow of geometry setup, field dump, and result visualization.

This tutorial covers:

  • FDTD setup with sinusoidal excitation and mixed boundary conditions

  • Geometry and field-dump definition using CSXCAD

  • Geometry inspection with AppCSXCAD

  • Time-domain E-field animation in Paraview

Octave/Matlab Script

FDTD Parameters and Boundary Conditions

Run 100 time steps with a 10 MHz sinusoidal excitation to reach steady state quickly. PEC boundaries on ±y model the conducting plates; PMC on ±x makes the structure periodic in x; Mur ABCs on ±z absorb outgoing waves.

% init and define FDTD parameter
FDTD = InitFDTD(200,0,'OverSampling',50);
FDTD = SetSinusExcite(FDTD,10e6);
BC = {'PMC' 'PMC' 'PEC' 'PEC' 'MUR' 'MUR'};
FDTD = SetBoundaryCond(FDTD,BC);

CSXCAD Geometry and Mesh

All coordinates are in metres. The uniform 1 m mesh spans ±10 m in x and y (the plate aperture) and −10 to 30 m in z, giving 30 cells of propagation distance beyond the source plane.

% init and define FDTD mesh
CSX = InitCSX();
mesh.x = -10:10;
mesh.y = -10:10;
mesh.z = -10:30;
CSX = DefineRectGrid(CSX, 1, mesh);

Excitation

A y-polarised (E_y) uniform-field source at z = 0 launches the TEM mode. The excitation box covers the full cross-section to produce a spatially uniform plane-wave front.

% define the excitation
CSX = AddExcitation(CSX,'excitation',0,[0 1 0]);
CSX = AddBox(CSX,'excitation',0,[-10 -10 0],[10 10 0]);

Field Dump

Record the time-domain E-field in the xz mid-plane (y = 0) so Paraview can animate wave propagation along z after the simulation completes.

% define a time domain e-field dump box
CSX = AddDump(CSX,'Et','DumpMode',1);
CSX = AddBox(CSX,'Et',0,[-10 0 -10],[10 0 30]);

Write, Visualize and Run

Serialize the model to XML, open AppCSXCAD to verify the geometry, then launch the FDTD engine. Load the Et_*.vtr output files in Paraview to animate the propagating wave.

% remove old simulation results (if exist)
CleanupSimPath('tmp');

% write openEMS xml data file
WriteOpenEMS('tmp/tmp.xml',FDTD,CSX);

% view defined structure
CSXGeomPlot( 'tmp/tmp.xml' );

% run openEMS simulation
RunOpenEMS('tmp','tmp.xml','-vvv');

disp('use Paraview to visualize the FDTD result...');

Inspecting the Geometry

After running CSXGeomPlot, AppCSXCAD opens and shows the simulation domain in the xy-plane. The excitation box appears in blue covering the full cross-section; the E-field dump plane (xz mid-plane at y = 0) appears as a red line.

AppCSXCAD view of the parallel plate waveguide

AppCSXCAD geometry view — excitation box (blue) and dump plane (red line)

Visualizing Results in Paraview

After the simulation, openEMS writes the E-field dump to tmp/Et_*.vtr. To animate the propagating wave in Paraview:

  1. File → Open and select the Et_*.vtr file.

  2. Click Apply in the Properties panel.

  3. Set Color by to E-Field in the Display properties.

  4. Press Play in the Animation toolbar.

  5. Use Rescale to Data Range occasionally to tune the colour mapping.

For a clearer view of wave propagation, apply a Warp By Vector filter (Filters → Alphabetical → Warp By Vector, then Apply).

Paraview visualization of the E-field

Paraview animation of the propagating TEM-mode E-field