Double-Ridged Horn Antenna

A double-ridged horn antenna is popularly used in an anechoic chamber to characterize an antenna under test (AUT) from S-band to Ku-band due to its reliable performance in a wideband frequency range. The model computes the voltage standing wave ratio (VSWR), far-field radiation pattern, and antenna directivity.

Figure 1: Double-ridged horn antenna excited by a coaxial port. The surrounding air domain and a perfectly matched layer, which is required for the simulation, are not included in this figure.

This example requires the RF Module and the Design Module.

Model Definition

The simulation frequency range is from 2 GHz to 6 GHz. The conductivity of the metallic material in the model is assumed to be high enough to neglect the loss in the given frequency range. Thus, all metal parts are modeled using a perfect electric conductor (PEC) feature. An exponential function, e0.028x is used in a parametric curve to create the tapered metallic ridges that are excited by an SMA type dielectric-filled coaxial connector. A lumped port is assigned on the boundary between the inner and outer conducting surface at the end of the coaxial connector. The antenna is enclosed by a spherical air domain. The outermost layer of the air domain is configured as a perfectly matched layer (PML) where the thickness of the layer is slightly greater than 0.1 wavelengths at the lowest simulation frequency. The PML absorbs all outgoing radiation from the antenna and work as an anechoic chamber during the simulation. The mesh is controlled by the Electromagnetic Waves, Frequency Domain physics interface and it has to be defined dynamically based on each simulation frequency, so frequency parametric sweep is over Frequency Domain study step.

Results and Discussion

In Figure 2, the slice and contour plot of Ez is visualized in the zx-plane. The electric field is guided by two symmetric metallic ridges and propagating toward the aperture of the horn.

Figure 2: z-component of the electric field and its contour plot at 6 GHz.

Figure 3 shows the 3D far-field radiation pattern. When it is plotted, the directivity is also calculated which is around 12.9 dB. Other antenna far-field postprocessing variables such as antenna gain and axial ratio can be visualized using the same plot by replacing the default input fields both for expression and color. These steps are not included in this tutorial but you are encouraged to try.

Figure 3: 3D far-field radiation pattern that is directive toward the open aperture.

Voltage standing wave ratio (VSWR) is a measure commonly used to characterize the input impedance matching properties for off-the-shelf antenna products. Figure 4 presents the VSWR of the double-ridged horn antenna that is lower than 1.7 in the simulated frequency range.

Figure 4: Voltage standing wave ratio (VSWR) plot. It is better than 2:1 in the simulated frequency range

Notes About the COMSOL Implementation

The antenna model is memory intensive and requires more than 12 GB RAM for the simulation up to 6 GHz. It may require much more for higher frequency simulations.

RF_Module/Antennas/double_ridged_horn_antenna

Modeling Instructions

From the menu, choose .

New

In the window, click

Model Wizard

In the window, click

In the tree, select .

Click .

Click

In the tree, select .

Click

Global Definitions

Parameters 1

In the window, under click .

In the window for , locate the section.

In the table, enter the following settings:


Name	Expression	Value	Description
w_slot	1.8[mm]	0.0018 m	Slot width
f0	2[GHz]	2E9 Hz	Frequency

Study 1

Step 1: Frequency Domain

In the window, under click .

In the window for , locate the section.

In the text field, type f0.

Geometry 1

In the window, under click .

In the window for , locate the section.

From the list, choose .

Locate the section. From the list, choose .

Work Plane 1 (wp1)

In the toolbar, click

In the window for , locate the section.

From the list, choose .

In the text field, type 3.5.

Work Plane 1 (wp1)>Plane Geometry

In the window, click .

Work Plane 1 (wp1)>Parametric Curve 1 (pc1)

In the toolbar, click

and choose .

In the window for , locate the section.

In the text field, type 150.

Locate the section. In the text field, type s-100.

In the text field, type exp(0.028*s)-1+w_slot/2.

Work Plane 1 (wp1)>Mirror 1 (mir1)

In the toolbar, click

and choose .

Select the object only.

In the window for , locate the section.

Select the check box.

Locate the section. In the text field, type 0.

In the text field, type 1.

Work Plane 1 (wp1)>Rectangle 1 (r1)

In the toolbar, click

In the window for , locate the section.

In the text field, type 20.15.

In the text field, type w_slot.

Locate the section. In the text field, type -120.15.

In the text field, type -w_slot/2.

Click

Click the

button in the toolbar.

Work Plane 1 (wp1)>Rectangle 2 (r2)

In the toolbar, click

In the window for , locate the section.

In the text field, type 20.15.

In the text field, type 30.

Locate the section. In the text field, type -120.15.

In the text field, type -15.

Work Plane 1 (wp1)>Polygon 1 (pol1)

In the toolbar, click

In the window for , locate the section.

From the list, choose .

In the text field, type 50 -100 -100 -100 -100 50.

In the text field, type exp(0.028*150)-1+w_slot/2 15 15 -15 -15 -(exp(0.028*150)-1+w_slot/2).

Extrude 1 (ext1)

In the window, right-click and choose .

In the window for , locate the section.

In the table, enter the following settings:


Distances (mm)
7

Work Plane 2 (wp2)

In the toolbar, click

In the window for , locate the section.

From the list, choose .

In the text field, type 50.

Work Plane 2 (wp2)>Plane Geometry

In the window, click .

Work Plane 2 (wp2)>Rectangle 1 (r1)

In the toolbar, click

In the window for , locate the section.

In the text field, type 190.

In the text field, type (exp(0.028*150)-1+w_slot/2)*2.

Locate the section. In the text field, type -95.

In the text field, type -(exp(0.028*150)-1+w_slot/2).

Work Plane 3 (wp3)

In the window, right-click and choose .

In the window for , locate the section.

From the list, choose .

In the text field, type -100.

Work Plane 3 (wp3)>Plane Geometry

In the window, click .

Work Plane 3 (wp3)>Rectangle 1 (r1)

In the toolbar, click

In the window for , locate the section.

In the text field, type 50.

In the text field, type 30.

Locate the section. In the text field, type -25.

In the text field, type -15.

Extrude 2 (ext2)

In the window, right-click and choose .

In the window for , locate the section.

From the list, choose .

Locate the section. In the table, enter the following settings:


Distances (mm)
28

Select the check box.

Loft 1 (loft1)

In the toolbar, click

Click the

button in the toolbar.

Click the

button in the toolbar.

Select the objects and only.

Cylinder 1 (cyl1)

In the toolbar, click

In the window for , locate the section.

In the text field, type 2.05.

In the text field, type 15-w_slot/2.

Locate the section. In the text field, type -117.5.

In the text field, type w_slot/2.

Cylinder 2 (cyl2)

Right-click and choose .

In the window for , locate the section.

In the text field, type 0.635.

In the text field, type 15+w_slot/2.

Locate the section. In the text field, type -w_slot/2.

Part Libraries

In the toolbar, click

and choose .

In the window, click .

In the window, select in the tree.

Click

Geometry 1

SMA Connector, Flange with Two Holes 1 (pi1)

In the window, under click .

In the window for , locate the section.

In the table, enter the following settings:


Name	Expression	Value	Description
solder_o	0	0	Soldering block option

Locate the section. Find the subsection. In the text field, type -117.5.

In the text field, type 15.

Find the subsection. From the list, choose .

In the text field, type 90.

Click to expand the section. In the table, enter the following settings:


Name	Keep	Physics	Contribute to
Exterior		√	None
Conductive surface	√	√	None

Click to expand the section. In the table, enter the following settings:


Name	Keep	Physics	Contribute to
All		√	None
Dielectric	√	√	None
Conductor		√	None

Click

Sphere 1 (sph1)

In the toolbar, click

In the window for , locate the section.

In the text field, type 170.

Click to expand the section. In the table, enter the following settings:


Layer name	Thickness (mm)
Layer 1	20

In the toolbar, click

Definitions

Perfectly Matched Layer 1 (pml1)

In the toolbar, click

Select Domains 1–4 and 24–27 only.

In the window for , locate the section.

From the list, choose .

Add Material

In the toolbar, click

to open the window.

Go to the window.

In the tree, select .

Right-click and choose .

In the toolbar, click

to close the window.

Materials

Material 2 (mat2)

In the window, under right-click and choose .

Select Domain 12 only.

In the window for , locate the section.

In the table, enter the following settings:


Property	Variable	Value	Unit	Property group
Relative permittivity	epsilonr_iso ; epsilonrii = epsilonr_iso, epsilonrij = 0	2.1	1	Basic
Relative permeability	mur_iso ; murii = mur_iso, murij = 0	1	1	Basic
Electrical conductivity	sigma_iso ; sigmaii = sigma_iso, sigmaij = 0	0	S/m	Basic

Material 3 (mat3)

Right-click and choose .

In the window for , locate the section.

From the list, choose .

Electromagnetic Waves, Frequency Domain (emw)

Perfect Electric Conductor 2

In the window, under right-click and choose .

In the window for , locate the section.

Click

In the dialog box, type 13-17, 28-30, 33-36, 45, 47, 50, 51, 53, 54, 66, 69-73, 75-79, 81, 82, 94, 95, 98-101, 103-106, 108, 109, 122, 124-126, 128, 129, 132, 134-136, 138, 139, 141-143 in the text field.

Click .