Vivaldi Antenna

A tapered slot antenna, also known as a Vivaldi antenna, is useful for wideband applications. Here, an exponential function is used for the taper profile. The objective of this example is to compute the far-field pattern and to compute the impedance of the structure. Good matching is observed over a wide frequency band.

Figure 1: The Vivaldi antenna is realized on a thin dielectric substrate. The entire domain is bounded by a perfectly matched layer.

Model Definition

In this Vivaldi antenna model, the tapered slot is patterned with a perfect electric conductor (PEC) ground plane on the top of the dielectric substrate. A simple exponential function, e0.044x is used to create the tapered slot curves. One end of the slot is open to air and the other end is finished with a circular slot. On the bottom of the substrate, the shorted 50 Ω microstrip feed line is modeled as PEC surfaces. The entire modeling domain is bounded by a perfectly matched layer (PML) which acts like an anechoic chamber absorbing all radiated energy. To excite the antenna, a lumped port is used. The model is meshed using a tetrahedral mesh with approximately five elements per wavelength in each material and simulation frequency.

Results and Discussion

The simulated SWR plot, Figure 2, shows good wideband matching properties. A Vivaldi antenna utilizes traveling waves generating a directive radiation pattern toward the open end of the tapered slot. The 3D far-field pattern in Figure 3 shows a directive radiation pattern.

Figure 2: The frequency response SWR of the Vivaldi antenna shows wideband impedance matching, better than 2:1 in most of the simulated frequency range.

Figure 3: 3D far-field pattern at 5.5 GHz shows a directional radiation pattern.

RF_Module/Antennas/vivaldi_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

Study 1

Step 1: Frequency Domain

In the window, under click .

In the window for , locate the section.

In the text field, type range(2[GHz],0.5[GHz],6.5[GHz]).

Geometry 1

In the window, under click .

In the window for , locate the section.

From the list, choose .

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
thickness	60[mil]	0.001524 m	Substrate thickness
w_slot	0.5[mm]	5E-4 m	Slot with

Here, mil refers to the unit milliinch.

Geometry 1

Create a block for the antenna substrate.

Substrate

In the toolbar, click

In the window for , type Substrate in the text field.

Locate the section. In the text field, type 110.

In the text field, type 80.

In the text field, type thickness.

Locate the section. From the list, choose .

Next, add a block for the 50Ω microstrip feed line.

Feed line

In the toolbar, click

In the window for , type Feed line in the text field.

Locate the section. In the text field, type 3.2.

In the text field, type 40+w_slot/2.

In the text field, type thickness.

Locate the section. From the list, choose .

In the text field, type -26.

In the text field, type -20+w_slot/4.

Next, create a work plane where you will draw the Vivaldi antenna pattern. Use two parametric curves for the tapered slot.

Work Plane 1 (wp1)

In the toolbar, click

In the window for , locate the section.

In the text field, type thickness/2.

Click

Work Plane 1 (wp1)>Plane Geometry

Click the

button in the toolbar.

Add a parametric curve using the exponential profile.

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 70.

Locate the section. In the text field, type s-15.

In the text field, type exp(0.044*s)-1+w_slot/2.

Generate the other parametric curve by mirroring the first one.

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

In the toolbar, click

and choose .

In the window for , locate the section.

In the text field, type 1.

In the text field, type 0.

Locate the section. Select the check box.

Select the object only.

Click

Add a rectangle describing the thin slot connected to the tapered slot.

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

In the toolbar, click

In the window for , locate the section.

In the text field, type 20.

In the text field, type w_slot.

Locate the section. In the text field, type -35.

In the text field, type -w_slot/2.

Add a circle attached to the end of the slot.

Work Plane 1 (wp1)>Circle 1 (c1)

In the toolbar, click

In the window for , locate the section.

In the text field, type 12.

Locate the section. In the text field, type -40.5.

Create a union of the circle and the rectangle to remove unnecessary boundaries.

Work Plane 1 (wp1)>Union 1 (uni1)

In the toolbar, click

and choose .

Select the objects and only.

In the window for , locate the section.

Clear the check box.

In the toolbar, click

Add a sphere for the PMLs. Use a layer definition to create a shell-type structure.

PML

In the window, right-click and choose .

In the window for , type PML in the text field.

Locate the section. In the text field, type 110.

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


Layer name	Thickness (mm)
Layer 1	30

Click

Click the

button in the toolbar.

Choose wireframe rendering to get a better view of the interior parts.

Click the

button in the toolbar.

Definitions

Add a perfectly matched layer.

Perfectly Matched Layer 1 (pml1)

In the toolbar, click

Select Domains 1–4 and 8–11 only.

In the window for , locate the section.

From the list, choose .

Hide some domains to get a better view of the interior parts when setting up the physics and reviewing the mesh.

Hide for Physics 1

In the window, right-click and choose .

Select Domains 2 and 9 only.

Hide for Physics 2

Right-click and choose .

In the window for , locate the section.

From the list, choose .

Select Boundaries 10 and 36 only.

Electromagnetic Waves, Frequency Domain (emw)

Now set up the physics. Use the selections already defined when assigning boundary conditions.

Perfect Electric Conductor 2

In the window, under right-click and choose .

Select Boundaries 16, 21, 22, 24, and 27 only.

Far-Field Domain 1

In the toolbar, click

and choose .

Lumped Port 1

In the toolbar, click

and choose .

Click the

button in the toolbar, a couple of times to get a better view.

Select Boundary 20 only.

For the first port, wave excitation is by default.

Materials

Assign material properties for the model. First, use air for all domains.

Add Material

In the toolbar, click

to open the window.

Go to the window.

In the tree, select .

Click in the window toolbar.

In the toolbar, click

to close the window.

Materials

Air (mat1)

Override the substrate with a dielectric material of εr = 3.38.

Substrate

In the window, right-click and choose .

In the window for , type Substrate in the text field.

Select Domains 6 and 7 only.

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	3.38	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