Antenna Array 2D (antennaArray2D.sdf)

Keywords:

antennaArray2D, far field, radiation, s-parameters

Problem Description

This set of 2-D XSimEM simulations shows how to obtain the far fields, S11 parameter, gain, and phase shift of a one-element antenna as well as the far fields, gain, S parameters, and phase shift of a multiple-element antenna array with one excited element. These simulations can be used as a basis for measuring coupling in phased array antennas. The analyzer compute2DantennaGainAndPhase.py is set up to calculate the S parameter for the excited element and any other reference element defined by the constant S_PARAM_ELEM.

Opening the Simulation

The Antenna Array 2D example is accessed from within XSimComposer by the following actions:

  • Select the New → From Example… menu item in the File menu.

  • In the resulting Examples window expand the XSim for Electromagnetics option.

  • Expand the Antennas option.

  • Select Antenna Array 2D and press the Choose button.

  • In the resulting dialog, create a New Folder if desired, then press the Save button to create a copy of this example.

The resulting Setup Window is shown Fig. 151.

image 1

Fig. 151 Setup Window for the Antenna Array 2D example.

Simulation Properties

The antennas are waveguide apertures excited with a frequency of 1 GHz and the aperture width is \(0.1\lambda\) (see the parameter GAP in the element tree). The distance between the gaps is \(0.4\lambda\). Below, other geometry options will be discussed (e.g. single aperture antenna).

Running the Multi-Aperture Antenna Simulation

Once finished with the setup, continue as follows:

  • Proceed to the Run Window by pressing the Run button in the navigation column out left.

  • To run the file, click on the Run button in the upper left corner of the Logs and Output Files pane. You will see the output of the run in that pane. The run has completed successfully when you see the output, “Engine completed successfully.”

  • First run settings (default):

    • Number of Steps: 6000

    • Dump Periodicity: 3000

    • Dump at Time Zero: box checked

After the first run completes, proceed as follows:

  • Second run settings:

    • Number of Steps: 1800

    • Dump Periodicity: 45 (Value taken from the parameter DUMP_PER_SECOND_RUN)

    • Set Restart at Dump Number to 2

Note

If the grid properties change, these values will have to be adjusted.

The end of the second run is shown in Fig. 152.

image 1

Fig. 152 The Run Window at the end of the second run execution.

Visualizing the Results

After performing the above actions, the results can be visualized as follows:

  • Proceed to the Visualize Window by pressing the Visualize button in the navigation column

  • Expand Scalar Data in the Visualization Controls pane

  • Expand E

  • Select E_x

  • Check the box for Set Minimum and set it to -100

  • Check the box for Set Maximum and set it to 100

  • Select the dump slider and move it to higher dump numbers to see the evolution of the electric field in time.

The resulting visualization is shown in Fig. 153.

image 1

Fig. 153 The near and far electric fields in the x-direction at the end of the simulation.

Figure Fig. 153 shows the near and far electric fields at the end of the simulation run. The dispersion of the electric field through the non-excited waveguides can also be seen.

Calibration Simulation

For both the multiple-element and single-element antenna simulations, calibration runs are needed for the analyzer.

For the original multiple-element array setup, proceed as follows:

  • Proceed to the Setup Window

  • In the top left corner, select File → Save Simulation As …

  • Rename the simulation to antennaArray2DCalibration.sdf

Note

If your simulation has a different name, add the word Calibration before .sdf

  • Click Save

  • Expand Geometries

  • Expand CSG

  • Deactivate array

  • Deactivate gapArray

  • Select gap

  • Change the height by right clicking on the Value → Assign Parameter → HEIGHT_METAL_CALIB

  • Change the x position by right cliking on the Value → Assign Parameter → XBGN_EXCITED_GAP

  • Select metal

  • Change the height by right clicking on the Value → Assign Parameter → HEIGHT_METAL_CALIB

  • Click on metal, hold down Ctrl (Cmd on Mac) and select gap right click → Boolean Operation → metal - gap

  • Select metalMinusgap

  • Select PEC under material from the drop-down menu.

You can now assign any name of your choice to the metalMinusgap geometry (e.g., myWaveguide).

  • Expand Field Dynamics

  • Expand FieldBoundaryConditions

  • Remove openUpperY

  • Right-click FieldBoundaryConditions → Add FieldBoundaryCondition → select Port

  • Select upper y for the boundary surface from the drop-down menu

  • Save and proceed to the Run tab.

  • Change Number of Steps to 7800 then click the Run button

Note

The calibration number of steps must equal the total number of steps that the simulation ran for during the regular run.

Analyzing the Results

After runnign the Calibration Simulation, continue as follows:

  • Re-open the original antennaArray2D simulation by File → Recent Simulations → antennaArray2D.sdf

  • Proceed to the Analysis Window by pressing the Analyze button in the navigation column.

  • Open the compute2DantennaGainAndPhase.py analyzer by selecting it and selecting “open”.

  • The default analyzer fields are the following:

    • simulationName: antennaArray2D

    • dumpNr: 30

    • nlambda: 15.0

    • gapWidth: 0.03

    • center: 0.0,-4.4969

    • dt: 5.59290428954e-12

    • freq: 1000000000.0

  • The overwrite box should be checked

  • Click Analyze in the top right corner.

  • The analysis is completed when you see the output shown in Fig. 154.

image 1

Fig. 154 The S-parameters for the excited element as well as the reference element associated with the constant S_PARAM_ELEM in the simulation setup are shown at the end of the analyzer run.

The S-parameters for the excited element as well as the reference element associated with the constant S_PARAM_ELEM in the simulation setup are shown at the end of the analyzer run.

This analyzer creates a text file with 5 columns. The first column is the theta direction in degrees, the second column is the analytical gain of the ISOLATED excited element in dB, the third column is the gain measured by XSim in dB, the fourth column is the analytical phase of the ISOLATED excited element in degrees, and the fith column is the phase measured by XSim in degrees. The name of the text file is antennaArray2D_gainAndPhaseData.txt.

For the default simulation settings (i.e., the center element of a 25-element array is excited while the other elements are turned off), plotting the second and third columns (analytical and measured gains) against the first column (as a function of theta) will give the results shown in Fig. 155. These can be plotted in the analysis software of your choice (e.g. Python, Matlab, IDL)

image 1

Fig. 155 The gain pattern of a 25-element array with the center excited element.

Plotting the fourth and third columns (analytical and measured field phases) against the first column (as a function of theta) will give the results shown in Fig. 156.

image 1

Fig. 156 The phase pattern of a 25-element array with the center excited element.

This concludes the multi-aperture antenna simulation and analysis.

Single Element Antenna Simulation

The geometry can be modified to simulate a single-aperture antenna. To do this:

  • Expand Constants

  • Change constants N_ELEM to 1

  • Change N_EXCITED_ELEM to 1

  • Expand Geometries

  • Expand CSG

  • Deactivate array

  • Select metal, hold Ctrl (Cmd on Mac), select gap, right click → Boolean Operation → select metal - gap

  • Select metalMinusgap

  • For material select PEC from the drop-down menu

If you want, you can now assign any name of your choice to the metalMinusgap geometry (e.g., aperture). Save and proceed to the Run tab. Follow the same run steps as described above in the section Running the Multi-Aperture Antenna Simulation.

Second vizualization results are shown in Fig. 157.

image 1

Fig. 157 The near and far electric fields in the x-direction for a 1-element antenna.

A calibration run can be done for this simulation in the same way it was done in section Calibration Simulation.

Further Experiments

A different array of geometries can be created changing input parameters such as number of elements in the array (N_ELEM) and the distance between the elements in each direction (DIST_ELEM). After changing these Constants, to create a different antenna array, proceed as follows:

  • Expand Geometries

  • Expand CSG

  • Right-click on gap → Create Array

In the Array Description window, select the “Union elements” checkbox, type in the number of elements to the value under N_ELEM, and the distance between elements to the value under DIST_ELEM. Then select the CSG “metal”, hold down Ctrl and select gapElemUnion located at the end of the gap array elements → Boolean Operation → select metal_gapElemUnion. Rename accordingly and assign the material PEC to the newly created geometry.

Repeating the analysis steps for a 1-element antenna (N_ELEM = 1 in the simulation setup) will give the results shown in Fig. 158 and Fig. 159.

image 1

Fig. 158 The gain pattern of a 1-element array.

image 1

Fig. 159 The phase pattern of a 1-element array.

A different element can be excited by changing input parameter N_EXCITED_ELEM.

Repeating the analysis steps for a 25-element antenna with the edge element excited (N_EXCITED_ELEM = 25 in the simulation setup) will give the results shown in Fig. 160 and Fig. 161.

image 1

Fig. 160 The gain pattern of a 25-element array with the edge excited element.

image 1

Fig. 161 The phase pattern of a 25-element array with the edge excited element.