Dielectric Resonator Antenna

In this example, a slot antenna is augmented by placing a dielectric block structure above the antenna. This block has additional metallic elements patterned on it that act as a lens and guide the radiation pattern and increase the directivity. The model is shown in Figure 1.

Figure 1: Slot coupled dielectric resonator antenna with parasitic arrays. Only one-quarter of the entire PMLs are shown in this figure.

Model Definition

A slot antenna is formed by cutting out a rectangular section from a ground plane. This slot antenna is fed from a 50 Ω. microstrip line which is fed from a 50 Ω. lumped port, representing the power source. The microstrip line extends some distance past the slot, forming a tuning stub. Both the ground plane and the microstrip line are treated as being infinitely thin, and are assumed to be perfect electric conductor (PEC) surfaces.

A block of quartz dielectric, is placed above the slot antenna. This block acts as a resonant structure, but also as a radiating element. The directivity of the radiation pattern is improved by patterning additional metal layers onto the block. In this example, two strips are added along the top, and two loops are added along each face. These layers are modeled as infinitely thin PEC faces. The dimensions of these elements are chosen such that they are resonant at the operating frequency of 2.9 GHz. These additional unfed elements act to increase the directivity of the antenna structure.

The entire antenna structure is modeled within a sphere with the properties of vacuum. This sphere is truncated by a perfectly matched layer (PML) domain that acts as a boundary to free space. The distance from the antenna to the PML is a variable that does require some study. The PML should not be within the reactive near-field region of the antenna structure. However, the size of the reactive near-field is not strictly definable, so the distance from the antenna to the PML should be studied for each model. It should be placed far enough away as not have negligible effect upon the results. The thickness of the PML itself is not critical, and can be made approximately one-tenth the air sphere diameter.

The meshing of radiating structures requires some care. As a rule of thumb, at least five elements per wavelength in each material are suggested, although if absolutely necessary, as few as three elements can be used. Additionally, curved edges and surfaces should be meshed with at least two elements per 90 ° chord, and the stricter of the two criteria should always be used. Additionally, tetrahedral elements of approximately unit aspect ratio are preferred in most modeling regions, with the exception of the PML domains. Since the PML domain preferentially absorbs radiated energy in one direction, the mesh should conform to this. A swept mesh is thus recommended in PML regions.

Results and Discussion

The structure is solved for an operating frequency of 2.9 GHz. The far-field radiation patterns are shown in Figure 2 and Figure 3. The radiation guided by the dielectric resonator and metallic strips is directional toward the top side.

Figure 2: Far-field radiation pattern on the E-plane at 2.9 GHz.

Figure 3: 3D far-field radiation pattern shows the directivity is increased by the dielectric resonator and the metallic strips.

RF_Module/Antennas/dielectric_resonator_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
thickness	20[mil]	5.08E-4 m	Substrate thickness
l_substrate	110[mm]	0.11 m	Length, substrate
w_line	1.13[mm]	0.00113 m	Width, feed line
l_line	40[mm]	0.04 m	Length, feed line
w_resonator	70[mm]	0.07 m	Width, dielectric resonator
l_resonator	25[mm]	0.025 m	Length, dielectric resonator
h_resonator	45[mm]	0.045 m	Height, dielectric resonator
w_matching	1.13[mm]	0.00113 m	Width, matching stub
l_matching	35.2[mm]	0.0352 m	Length, matching stub
w_slot	2.9[mm]	0.0029 m	Width, slot
l_slot	18.5[mm]	0.0185 m	Length, slot
d_array	30[mm]	0.03 m	Array displacement
f0	2.9[GHz]	2.9E9 Hz	Current frequency
lda0	c_const/f0	0.10338 m	Wavelength, air
h_max	0.2*lda0	0.020675 m	Maximum mesh element size, air

Here, mil refers to the unit milliinch. c_const is a predefined COMSOL constant for the speed of light in vacuum.

Geometry 1

First, create a block for the dielectric resonator.

Dielectric resonator

In the toolbar, click

In the window for , type Dielectric resonator in the text field.

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

In the text field, type l_resonator.

In the text field, type h_resonator.

Locate the section. From the list, choose .

In the text field, type h_resonator/2.

Add a block for the substrate.

Substrate

In the toolbar, click

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

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

In the text field, type l_substrate.

In the text field, type thickness.

Locate the section. From the list, choose .

In the text field, type -thickness/2.

Click the

button in the toolbar.

Add a block for the 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 w_line.

In the text field, type l_line.

In the text field, type thickness.

Locate the section. From the list, choose .

In the text field, type -l_line/2.

In the text field, type -thickness/2.

Add a block for the matching stub which is extended from the end of the feed line.

Matching stub

In the toolbar, click

In the window for , type Matching stub in the text field.

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

In the text field, type l_matching.

In the text field, type thickness.

Locate the section. From the list, choose .

In the text field, type l_matching/2.

In the text field, type -thickness/2.

Click

Then, add a work plane for the slot. The slot is located between the dielectric resonator and substrate.

Work Plane 1 (wp1)

In the toolbar, click

In the window for , click

Work Plane 1 (wp1)>Plane Geometry

In the window, click .

Create a rectangle for the slot.

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

In the toolbar, click

Click the

button in the toolbar.

In the window for , locate the section.

In the text field, type l_slot.

In the text field, type w_slot.

Locate the section. From the list, choose .

Click

Add a work plane on one of the side walls of the dielectric resonator. You may click Close in the current Work Plane toolbar to access the Geometry toolbar.

Work Plane 2 (wp2)

In the window, right-click and choose .

In the window for , locate the section.

From the list, choose .

On the object , select Boundary 3 only.

It might be easier to select the correct boundary by using the window. To open this window, in the toolbar click and choose . (If you are running the cross-platform desktop, you find in the main menu.)

Click

Work Plane 2 (wp2)>Plane Geometry

Create a circle for the ring strip.

Work Plane 2 (wp2)>Circle 1 (c1)

In the toolbar, click

Click the

button in the toolbar.

In the window for , locate the section.

In the text field, type 16.8[mm].

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


Layer name	Thickness (m)
Layer 2	1[mm]

Copy 1 (copy1)

Right-click and choose .

You may click Close in the current Work Plane toolbar to access the Geometry toolbar.

Select the object only.

In the window for , locate the section.

In the text field, type l_resonator.

Click

Add a work plane on the top of the dielectric resonator.

Work Plane 3 (wp3)

In the toolbar, click

In the window for , locate the section.

From the list, choose .

On the object , select Boundary 4 only.

Click

Work Plane 3 (wp3)>Plane Geometry

Create a rectangle for the short strip.

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

In the toolbar, click

Click the

button in the toolbar.

In the window for , locate the section.

In the text field, type 2[mm].

In the text field, type l_resonator.

Locate the section. From the list, choose .

In the text field, type -d_array/2.

Work Plane 3 (wp3)>Array 1 (arr1)

In the toolbar, click

and choose .

Select the object only.

In the window for , locate the section.

In the text field, type 2.

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

Click

Finish geometry creation by adding a sphere for the PMLs.

PMLs

Right-click and choose .

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

Locate the section. In the text field, type 0.11.

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


Layer name	Thickness (m)
Layer 1	0.02

Click

Click the

button in the toolbar.

The finished geometry describes the dielectric resonator antenna on a thin substrate enclosed by PMLs.

Definitions

Perfectly Matched Layer 1 (pml1)

In the toolbar, click

Select Domains 1–4 and 10–13 only.

In the window for , locate the section.

From the list, choose .

Create a set of selections for use before setting up the physics. First, create a selection for the substrate.

Substrate

In the toolbar, click

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

Select Domains 6, 8, and 9 only.

Add selections for the dielectric resonator, microstrip line, ground plane, and metal strips.

Dielectric resonator

In the toolbar, click

In the window for , type Dielectric resonator in the text field.

Select Domain 7 only.

Microstrip line

In the toolbar, click

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

Locate the section. From the list, choose .

Select Boundaries 34 and 40 only.

Ground plane

In the toolbar, click

In the window for , type Ground plane in the text field.

Locate the section. From the list, choose .

Select Boundaries 16, 20, 35, 36, 42, 43, and 66 only.

Metal strips

In the toolbar, click

In the window for , type Metal strips in the text field.

Locate the section. From the list, choose .

Select Boundaries 23–27, 52, 53, 62, 63, and 69 only.

Click the

button in the toolbar.

To get a better view, suppress some of the boundaries. Furthermore, by assigning the resulting settings to a View node, you can easily return to the same view later by clicking the button in the toolbar.

In the toolbar, click

Click the

button in the toolbar.

Hide for Physics 1

Right-click and choose .

In the window for , click

Select Domains 2, 5, and 11 only.

Electromagnetic Waves, Frequency Domain (emw)

Perfect Electric Conductor 2

In the window, under right-click and choose .

In the window for , locate the section.

From the list, choose .

Perfect Electric Conductor 3

In the toolbar, click

and choose .

In the window for , locate the section.

From the list, choose .

Perfect Electric Conductor 4

In the toolbar, click

and choose .

In the window for , locate the section.

From the list, choose .

Lumped Port 1

In the toolbar, click

and choose .

Click the

button in the toolbar, a couple of times to see the port boundary clearly.

Select Boundary 33 only.

For the first port, wave excitation is by default.

Click the

button in the toolbar.

Far-Field Domain 1

In the toolbar, click

and choose .

Materials

Next, assign material properties on the model. Begin by specifying 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.

Materials

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

Substrate

In the window, under right-click and choose .

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

Locate the section. From the list, choose .

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