# Half-Wave Dipole in Free Space (halfWaveDipoleAntennaT.pre)

Keywords:

halfWaveDipoleAntennaT, far field, radiation

## Problem Description

This problem illustrates how to obtain far field radiation patterns from VSim simulation data. The simulation itself consists of a half-wavelength long current source in free space.

This simulation can be performed with a VSimEM license.

## Opening the Simulation

The Half Wave Dipole Antenna example is accessed from within VSimComposer by the following actions:

• Select the New From Example… menu item in the File menu.
• In the resulting Examples window expand the VSim for Electromagnetics option.
• Expand the Antennas (text-based setup) option.
• Select “Half Wave Dipole in Free Space (text-based setup)” and press the Choose button.
• In the resulting dialog, create a New Folder if desired, and press the Save button to create a copy of this example.

The basic variables of this problem should now be alterable via the text boxes in the left pane of the Setup Window, as shown in Fig. 206.

Fig. 206 Setup Window for the Half Wave Dipole Antenna example.

## Input File Features

This file allows the modification of antenna operating frequency, as well as simulation domain size and far field resolution. It is also possible to perform this computation with a GPU.

## Running the Simulation

After performing the above actions, continue as follows:

• Proceed to the Run Window by pressing the Run button in the left column of buttons.
• To run the file, click on the Run button in the upper left corner. of the window. You will see the output of the run in the right pane. The run has completed when you see the output, “Engine completed successfully.” This is shown in the window below.

Fig. 207 The Run Window at the end of execution.

## Analyzing the Results

After performing the above actions, continue as follows:

• Proceed to the Analysis window by pressing the Analyze button in the left column of buttons.
• Click ‘Show All Analyzers’
• In the resulting dialog, select computeFarFieldFromKirhhoffBox.py and press Open.
• Input values for the analyzer parameters. The analyzer may be run multiple times, allowing the user to experiment with different values.
• simulationName - halfWaveDipoleAntennaT (name of the input file)
• fieldLabel - E (name of the electric field)
• farFieldRadius - 10.0 (distance to far field in m, 10.0 is a good value)
• timeStepStride - 3 (number of timesteps between far field calculations; determines how many far fields are output; 3 steps should yield 6 far fields in this case)
• getFourierComponent - 0 (whether to fourier analyze for a particular frequency)
• frequency - the frequency to use in the fourier analysis (not needed here).
• numTheta - 60 (number of theta points in the far field, 18 for a quick calculation, 45 for finer resolution)
• numPhi - 120 (number of phi points in the far field, 36 for a quick calculation, 90 for finer resolution)
• zeroThetaDirection - (0,0,1) (determines orientation of far field coordinate system)
• zeroPhiDirection - (1,0,0) (determines orientation of far field coordinate system
• varyingRadiusMesh - 0 (Set to 1 in order to make far field mesh adapt to magnitude of far field solution: the classic lobe view)
• simpsonIntegration - 0 (Set to 1 for more accurate integration)

Fig. 208 The Analysis window at the end of execution.

## Visualizing the Results

• Proceed to the Visualize Window by pressing the Visualize button in the left column of buttons.

The far field radiation pattern can be viewed as follows:

• Expand Scalar Data
• Expand farE
• Select farE_magnitude
• Expand Geometries
• Select farSphere
• Click and drag with your mouse to rotate the image

Fig. 209 The far field radiation pattern

## Further Experiments

The resolution of the far field pattern can be changed by editing the numTheta and numPhi values in the Analyzer Window.

To improve computational speed the size of the simulation domain can be optimized by adjusting LX/LY/LZ and PTS_PER_LAMBDA. Note that for far field calculations the simulation domain must be square.

If the Simulation domain is made to small, the results will be distorted as the entire near field must be within the simulation domain in order to acheive a proper transformation to the far field.