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Modeling a Biconical Antenna for EMI/EMC Testing
Introduction
Biconical antennas are popular for very high frequency (VHF) measurement because they support a wide frequency range. They are also useful for electromagnetic compatibility (EMC) testing where the antenna can be used as an RF source in susceptibility or immunity test. This example simulates a biconical antenna made of lightweight hexagonal frames that are preferred over solid cones for fabrication. The simulation includes the computation of far-field radiation pattern and voltage standing wave ratio (VSWR).
Figure 1: The frames of a biconical antenna are modeled as boundaries. The surrounding air domain and perfectly matched layers, which are required for the simulation, are not included in this figure.
Note: This example requires the RF Module and the Design Module.
Model Definition
The operating frequency of this example is in the conventional VHF frequency range from 60 MHz to 240 MHz. To simplify modeling steps and reduce the required computational resources, first, assume that the antenna frame structure is geometrically flat and very thin. However, the thickness is greater than the skin depth in the given frequency range so it is reasonable to model it as a perfect electric conductor.
A lumped port with a 50 Ω reference impedance is assigned to the gap located at the center of the two structures composed of hexagonal frames; lumped ports should be applied between two conducting boundaries.
The antenna is enclosed by a spherical air domain. The outermost layers of the air domain are configured as perfectly matched layers (PML) that absorb all outgoing radiation from the antenna and work as an anechoic chamber during the simulation.
Results and Discussion
Figure 2 presents the electric field distribution in dB, as well as an arrow plot showing the directional properties of the field at 70 MHz. It is observed that the electric field is confined to the entire structure when the frequency is in the lower range and the reacting area is gradually changed as the frequency increases.
The 2D far-field polar plot is visualized in Figure 3. The antenna is aligned along the z-axis and the radiation pattern is omnidirectional in the xy-plane. The 3D far-field radiation pattern in Figure 4 shows the same omnidirectional characteristics in the azimuthal direction. The computed VSWR (Figure 5) is approximately 3:1 on average.
Figure 2: Electric field distribution on the yz-plane in dB at 70 MHz. The electric field is resonant over the entire antenna structure.
Figure 3: Polar far-field plot on the xy-plane. The overall antenna gain is around 0 dBi.
Figure 4: 3D far-field pattern at 70 MHz. The pattern resembles that of a typical half-wave dipole antenna.
Figure 5: Voltage standing wave ratio (VSWR) plot with a log scale on the y-axis. It presents approximately a VSWR of 3:1 on average.
Application Library path: RF_Module/Antennas/biconical_frame_antenna
Modeling Instructions
From the File menu, choose New.
New
In the New window, click  Model Wizard.
Model Wizard
1
In the Model Wizard window, click  3D.
2
In the Select Physics tree, select Radio Frequency > Electromagnetic Waves, Frequency Domain (emw).
3
Click Add.
4
Click  Study.
5
In the Select Study tree, select General Studies > Frequency Domain.
6
Click  Done.
Study 1
Step 1: Frequency Domain
Define the study frequency ahead of performing any frequency-dependent operation such as building mesh. The physics-controlled mesh uses the highest frequency value in the specified range.
1
In the Model Builder window, under Study 1 click Step 1: Frequency Domain.
2
In the Settings window for Frequency Domain, locate the Study Settings section.
3
In the Frequencies text field, type range(60[MHz],10[MHz],240[MHz]).
Geometry 1
1
In the Model Builder window, under Component 1 (comp1) click Geometry 1.
2
In the Settings window for Geometry, locate the Advanced section.
3
From the Geometry representation list, choose CAD kernel.
Work Plane 1 (wp1)
1
In the Geometry toolbar, click  Work Plane.
2
In the Settings window for Work Plane, locate the Plane Definition section.
3
In the z-coordinate text field, type 2[cm].
Work Plane 1 (wp1) > Plane Geometry
In the Model Builder window, click Plane Geometry.
Work Plane 1 (wp1) > Rectangle 1 (r1)
1
In the Work Plane toolbar, click  Rectangle.
2
In the Settings window for Rectangle, locate the Size and Shape section.
3
In the Width text field, type 2[cm].
4
In the Height text field, type 2[cm]/2*sqrt(3).
5
Locate the Position section. In the xw text field, type -1[cm].
6
Click  Build Selected.
Work Plane 2 (wp2)
1
In the Model Builder window, right-click Geometry 1 and choose Work Plane.
2
In the Settings window for Work Plane, locate the Plane Definition section.
3
In the z-coordinate text field, type 50[cm].
4
Click  Go to Plane Geometry.
Work Plane 2 (wp2) > Rectangle 1 (r1)
1
In the Work Plane toolbar, click  Rectangle.
2
In the Settings window for Rectangle, locate the Size and Shape section.
3
In the Width text field, type 2[cm].
4
In the Height text field, type 40[cm].
5
Locate the Position section. In the xw text field, type -1[cm].
6
Click  Build Selected.
Copy 1 (copy1)
1
Right-click Geometry 1 and choose Transforms > Copy.
2
Select the object wp1 only.
3
In the Settings window for Copy, locate the Displacement section.
4
In the z text field, type 0.65.
5
Click  Build Selected.
6
Click the  Zoom Extents button in the Graphics toolbar.
Loft 1 (loft1)
1
In the Geometry toolbar, click  Loft.
2
Select the objects wp1 and wp2 only.
Loft 2 (loft2)
1
In the Geometry toolbar, click  Loft.
2
In the Settings window for Loft, click to expand the Start Profile section.
3
Click to select the  Activate Selection toggle button for Start profile.
4
On the object loft1, select Boundary 4 only.
It might be easier to select the correct boundary by using the Selection List window. To open this window, in the Home toolbar click Windows and choose Selection List. (If you are running the cross-platform desktop, you find Windows in the main menu.)
5
Click to expand the End Profile section. Click to select the  Activate Selection toggle button for End profile.
6
On the object copy1, select Boundary 1 only.
7
Click the  Wireframe Rendering button in the Graphics toolbar.
Delete Entities 1 (del1)
1
Right-click Geometry 1 and choose Delete Entities.
2
On the object loft2, select Boundaries 1, 2, 4–6, 10, and 11 only.
3
In the Settings window for Delete Entities, click  Build Selected.
Rotate 1 (rot1)
1
In the Geometry toolbar, click  Transforms and choose Rotate.
2
Select the object del1 only.
3
In the Settings window for Rotate, locate the Rotation section.
4
In the Angle text field, type 0 60 120 180 240 300.
5
Click  Build Selected.
Cylinder 1 (cyl1)
1
In the Geometry toolbar, click  Cylinder.
2
In the Settings window for Cylinder, locate the Size and Shape section.
3
In the Radius text field, type 5[mm].
4
In the Height text field, type 17.5[mm].
5
Locate the Position section. In the z text field, type 2.5[mm].
Rotate 2 (rot2)
1
In the Geometry toolbar, click  Transforms and choose Rotate.
2
Click the  Select All button in the Graphics toolbar.
3
In the Settings window for Rotate, locate the Rotation section.
4
In the Angle text field, type 0 180.
5
From the Axis type list, choose x-axis.
6
Locate the Selections of Resulting Entities section. Find the Cumulative selection subsection. Click New.
7
In the New Cumulative Selection dialog, By creating the selection of resulting entities, you can easily choose the all antenna radiator surfaces when setting up the physics later on.
8
type Antenna frame in the Name text field.
9
Click OK.
10
In the Settings window for Rotate, click  Build Selected.
11
Click the  Zoom Extents button in the Graphics toolbar.
Work Plane 3 (wp3)
1
In the Geometry toolbar, click  Work Plane.
2
In the Settings window for Work Plane, locate the Plane Definition section.
3
From the Plane list, choose zx-plane.
4
Click  Go to Plane Geometry.
Work Plane 3 (wp3) > Plane Geometry
Click the  Zoom In button in the Graphics toolbar, a few of times to get a view.
Work Plane 3 (wp3) > Rectangle 1 (r1)
1
In the Work Plane toolbar, click  Rectangle.
2
In the Settings window for Rectangle, locate the Size and Shape section.
3
In the Width text field, type 5[mm].
4
In the Height text field, type 10[mm].
5
Locate the Position section. In the xw text field, type -2.5[mm].
6
In the yw text field, type -5[mm].
7
Click  Build Selected.
Sphere 1 (sph1)
1
Right-click Geometry 1 and choose Sphere.
2
In the Settings window for Sphere, locate the Size section.
3
In the Radius text field, type 1.2.
4
Click to expand the Layers section. In the table, enter the following settings:
Layer name
Thickness (m)
Layer 1
0.3
5
In the Geometry toolbar, click  Build All.
6
In the Model Builder window, click Geometry 1.
Definitions
Perfectly Matched Layer 1 (pml1)
1
In the Definitions toolbar, click  Perfectly Matched Layer.
2
Select Domains 1–4 and 8–11 only.
These are all of the outermost domains of the sphere.
3
In the Settings window for Perfectly Matched Layer, locate the Geometry section.
4
From the Type list, choose Spherical.
Suppress some boundaries to get a better view when setting up materials, physics and mesh.
Hide for Physics 1
1
In the Model Builder window, right-click View 1 and choose Hide for Physics.
2
In the Settings window for Hide for Physics, locate the Geometric Entity Selection section.
3
From the Geometric entity level list, choose Boundary.
4
Select Boundaries 1, 5, 6, 9, 10, and 90–96 only.
Add Material
1
In the Materials toolbar, click  Add Material to open the Add Material window.
2
Go to the Add Material window.
3
In the tree, select Built-in > Air.
4
Click the Add to Component button in the window toolbar.
5
In the Materials toolbar, click  Add Material to close the Add Material window.
Electromagnetic Waves, Frequency Domain (emw)
Perfect Electric Conductor 2
1
In the Physics toolbar, click  Boundaries and choose Perfect Electric Conductor.
2
In the Settings window for Perfect Electric Conductor, locate the Boundary Selection section.
3
From the Selection list, choose Antenna frame.
Lumped Port 1
1
In the Physics toolbar, click  Boundaries and choose Lumped Port.
2
Click the  Zoom In button in the Graphics toolbar, a few of times to get a view.
3
Select Boundary 73 only.
For the first port, wave excitation is on by default.
Far-Field Domain 1
In the Physics toolbar, click  Domains and choose Far-Field Domain.
Mesh 1
1
In the Model Builder window, under Component 1 (comp1) click Mesh 1.
2
In the Settings window for Mesh, locate the Physics-Controlled Mesh section.
3
In the table, clear the Use checkbox for Geometric Analysis, Detail Size.
4
Click  Build All.
Study 1
Step 1: Frequency Domain
In the Study toolbar, click  Compute.
Results
Electric Field (emw)
The electric field distribution inside the PMLs is not of interest, so remove the PML domains from the visualization.
1
In the Model Builder window, expand the Results > Datasets node.
Multislice 1
Adjust the default E-field norm multislice plot.
1
In the Model Builder window, expand the Electric Field (emw) node, then click Multislice 1.
2
In the Settings window for Multislice, locate the Expression section.
3
In the Expression text field, type 20*log10(emw.normE).
4
Locate the Multiplane Data section. Find the Y-planes subsection. In the Planes text field, type 0.
5
Find the Z-planes subsection. In the Planes text field, type 0.
6
In the Electric Field (emw) toolbar, click  Plot.
Electric Field (emw)
Add an arrow plot.
Arrow Volume 1
1
In the Model Builder window, right-click Electric Field (emw) and choose Arrow Volume.
2
In the Settings window for Arrow Volume, locate the Arrow Positioning section.
3
Find the X grid points subsection. In the Points text field, type 1.
4
Find the Y grid points subsection. In the Points text field, type 21.
5
Find the Z grid points subsection. In the Points text field, type 21.
6
Locate the Coloring and Style section. From the Arrow type list, choose Cone.
7
From the Arrow length list, choose Normalized.
8
Select the Scale factor checkbox. In the associated text field, type 2e-4.
Color Expression 1
1
Right-click Arrow Volume 1 and choose Color Expression.
2
In the Settings window for Color Expression, locate the Expression section.
3
In the Expression text field, type 20*log10(emw.normE).
4
Locate the Coloring and Style section. Clear the Color legend checkbox.
5
Click to expand the Range section. Select the Manual color range checkbox.
6
In the Maximum text field, type 5.
Electric Field (emw)
1
In the Model Builder window, under Results click Electric Field (emw).
2
In the Settings window for 3D Plot Group, locate the Data section.
3
From the Parameter value (freq (GHz)) list, choose 0.07.
4
In the Electric Field (emw) toolbar, click  Plot.
5
Click the  Go to YZ View button in the Graphics toolbar.
See Figure 2 for the reproduced plot.
S-Parameter (emw)
In the Model Builder window, click S-Parameter (emw).
Smith Plot (emw)
In the Model Builder window, click Smith Plot (emw).
Electric Field, Logarithmic (emw)
In the Model Builder window, click Electric Field, Logarithmic (emw).
2D Far Field (emw)
1
In the Model Builder window, click 2D Far Field (emw).
2
In the Settings window for Polar Plot Group, locate the Axis section.
3
Select the Manual axis limits checkbox.
4
In the r minimum text field, type -20.
5
In the r maximum text field, type 2.
Radiation Pattern 1
1
In the Model Builder window, expand the 2D Far Field (emw) node, then click Radiation Pattern 1.
2
In the Settings window for Radiation Pattern, click Replace Expression in the upper-right corner of the Expression section. From the menu, choose Component 1 (comp1) > Electromagnetic Waves, Frequency Domain > Far field > emw.gaindBEfar - Far-field gain, dBi - dB.
3
In the 2D Far Field (emw) toolbar, click  Plot.
Figure 3 shows the 2D far-field gain polar plot.
3D Far Field, Gain (emw)
1
In the Model Builder window, under Results click 3D Far Field, Gain (emw).
2
In the Settings window for 3D Plot Group, locate the Data section.
3
From the Parameter value (freq (GHz)) list, choose 0.07.
4
In the 3D Far Field, Gain (emw) toolbar, click  Plot.
Figure 4 shows the 3D far-field radiation pattern.
VSWR
1
In the Results toolbar, click  1D Plot Group.
2
In the Settings window for 1D Plot Group, type VSWR in the Label text field.
Global 1
1
Right-click VSWR and choose Global.
2
In the Settings window for Global, click Add Expression in the upper-right corner of the y-Axis Data section. From the menu, choose Component 1 (comp1) > Electromagnetic Waves, Frequency Domain > Ports > emw.VSWR_1 - Voltage standing wave ratio - 1.
3
Click to expand the Coloring and Style section. Find the Line markers subsection. From the Marker list, choose Point.
VSWR
1
In the Model Builder window, click VSWR.
2
In the Settings window for 1D Plot Group, locate the Axis section.
3
Select the y-axis log scale checkbox.
4
Select the Manual axis limits checkbox.
5
In the y minimum text field, type 1.
6
In the y maximum text field, type 100.
7
In the VSWR toolbar, click  Plot.
Compare the VSWR plot with Figure 5.
3D Plot Group 9
In the Results toolbar, click  3D Plot Group.
Isosurface 1
1
Right-click 3D Plot Group 9 and choose Isosurface.
2
In the Settings window for Isosurface, locate the Expression section.
3
In the Expression text field, type 20*log10(emw.normE+0.1).
4
Locate the Levels section. In the Total levels text field, type 20.
5
Locate the Coloring and Style section. From the Color table transformation list, choose Nonlinear.
6
Set the Color calibration parameter value to -1.5.
Filter 1
1
Right-click Isosurface 1 and choose Filter.
2
In the Settings window for Filter, locate the Element Selection section.
3
In the Logical expression for inclusion text field, type x>0.
4
Click the  Go to Default View button in the Graphics toolbar.
5
Click the  Zoom In button in the Graphics toolbar.
Selection 1
1
In the Model Builder window, right-click Isosurface 1 and choose Selection.
2
Select Domain 5 only.
3
In the 3D Plot Group 9 toolbar, click  Plot.