COMSOL 6.4 - Mesh Adaptation Study for a Microstrip Patch Antenna

Mesh Adaptation Study for a Microstrip Patch Antenna

In electromagnetic design and simulation, optimizing the mesh configuration is important for achieving accurate results, especially for high-Q devices. This tutorial model showcases mesh adaptation using the Microstrip Patch Antenna model from the RF Module Application Library. It illustrates how to refine the mesh in critical regions to enhance computation accuracy through the Frequency Domain, RF Adaptive Mesh study. The adapted mesh focuses on refining around the edges of the patch radiator, while excluding areas with lower field strength. This approach ensures both computational efficiency and precise characterization of antenna performance.

Figure 1: Microstrip patch antenna after a mesh adaptation study.

Model Definition

After loading the Microstrip Patch Antenna model from the Application Library, two additional studies are conducted:

•

Frequency Domain, RF Adaptive Mesh for mesh refinement

•

Adaptive Frequency Sweep for S-parameter evaluation with fine frequency resolution using the refined mesh

Frequency Domain, RF Adaptive Mesh

The Frequency Domain, RF Adaptive Mesh is a dedicated mesh refinement study that dynamically refines the mesh in regions of interest by increasing the resolution around areas with high field variations. Functionally, it is similar to the Adaptation and Error Estimates in a Frequency Domain study, but with more streamlined settings tailored for RF devices. In the Frequency Domain, RF Adaptive Mesh study settings window, the default mesh refinement settings can be reviewed by switching the Mesh refinement option from Physics controlled to User controlled.

Notable settings include the Error estimate, which is set to Functional based on S-parameters. The Adaptation method uses the Rebuild mesh option and employs Goal-oriented termination with a maximum of 20 adaptation steps. The termination expression is the same as the one used in Functional, formulates with S-parameters.

Mesh refinement can be performed at a single frequency or across a bandwidth of the device under test. In this example, refinement is applied at 5 frequency points within the simulation bandwidth.

Adaptive Frequency Sweep

The Adaptive Frequency Sweep is useful for generating S-parameter plots with very fine frequency resolution. It uses the asymptotic waveform evaluation (AWE) method, which is more efficient than a regular discrete frequency sweep with fine frequency steps especially for single resonance devices or when the result scalar variable changes slowly across the simulation frequency spectrum. To manage the file size, particularly when dealing with many frequency points, consider storing output only from the Lumped port features. This approach significantly reduces file size dramatically preserving the S-parameter analysis results.

When this study is added, the mesh selection is automatically set to the refined mesh obtained from the previous study.

Results and Discussion

The this tutorial model demonstrates how mesh adaptation can be used to increase the result accuracy, by making the mesh finer in regions where it matters most for the results. Figure 2 shows the mesh after running the Frequency Domain, RF Adaptive Mesh study. Compared to the initial mesh, the adapted mesh is much finer around the patch edges, except where the field strength is low.

Figure 2: The mesh after running the Frequency Domain, RF Adaptive Mesh study.

Figure 3 shows how the mesh adaptation converges to reach the termination tolerance of 0.02.

Figure 3: This plot shows the convergence of the mesh adaptation process. The process stops when the tolerance of 0.02 is reached.

Finally, Figure 4 shows that the resonance shifts to higher frequencies when using the finer adapted mesh.

Figure 4: A comparison of the frequency spectra for the initial mesh and the adapted mesh.

Notes About the COMSOL Implementation

This example uses the Adaptive Frequency Sweep study, which employs the asymptotic waveform evaluation (AWE) model order reduction technique to compute the antenna’s frequency response with fine frequency resolution. This method is faster than a regular frequency sweep performed in a Frequency Domain study using the same frequency resolution, but it is computationally intensive, and may require more than 6 GB of RAM. The results can be sensitive to the relative tolerance value in the settings window, so using a finer value can improve the accuracy. The Frequency Domain, RF Adaptive Mesh study uses the Direct Solver and may requires more than 7 GB of RAM.

RF_Module/Antenna_Arrays/microstrip_patch_antenna_mesh_adaptation

Modeling Instructions

From the menu, choose .

Browse to the model’s Application Libraries folder and double-click the file microstrip_patch_antenna_inset.mph.

Study 1, Quadratic Discretization

In the window, click .

In the window for , type Study 1, Quadratic Discretization in the text field.

Study 2, Quadratic Discretization, AWE

In the window, click .

In the window for , type Study 2, Quadratic Discretization, AWE in the text field.

Locate the section. Clear the checkbox.

Add Study

If the loaded model does not have a solution, run the Study 2. Then, conduct a Frequency Domain, RF Adaptive Mesh study.

In the toolbar, click

to open the window.

Go to the window.

Find the subsection. In the tree, select > .

Click the button in the window toolbar.

In the toolbar, click

to close the window.

Study 3, Linear Discretization for Mesh Adaptation

In the window for , type Study 3, Linear Discretization for Mesh Adaptation in the text field.

Step 1: Frequency Domain, RF Adaptive Mesh

In the window, under click .

In the window for , locate the section.

Click

In the dialog, choose from the list.

In the text field, type freq_min.

In the text field, type freq_max.

In the text field, type 5.

Click .

In the window, click .

In the window for , locate the section.

Clear the checkbox, as the default S-parameter and far-field plots are not of interest for the mesh adaptation study. However, in the following steps a field plot is built, so the mesh adaptation progress can be followed while solving.

Solution 3 (sol3)

In the toolbar, click

, to create the dataset for this study. The field plot that will be created will refer to this dataset.

Results

Electric Field (emw), Mesh Adaptation

In the toolbar, click

In the window for , type Electric Field (emw), Mesh Adaptation in the text field.

Locate the section. From the list, choose .

Locate the section. Clear the checkbox.

Multislice 1

In the toolbar, click

and choose .

In the window for , locate the section.

Find the subsection. In the text field, type 0.

Locate the section. From the list, choose .

Selection 1

Right-click and choose .

In the window for , locate the section.

From the list, choose .

Electric Field (emw), Mesh Adaptation

In the window, under click .

In the window for , locate the section.

Clear the checkbox.

Surface 1

Right-click and choose .

In the window for , locate the section.

From the list, choose .

Selection 1

Right-click and choose .

In the window for , locate the section.

From the list, choose .

In the list, choose and .

Click

, to avoid that the mesh is visualized on the boundaries that otherwise are hidden in the physics view.

Select Boundaries 9, 11, 12, 32, 37, and 40 only.

Surface 2

In the window, under > right-click and choose , to add the first of two surface plots to visualize the mesh.

In the window for , locate the section.

In the text field, type 1.

Locate the section. From the list, choose .

From the list, choose .

Select the checkbox.

Surface 3

Right-click and choose .

Selection 1

In the window, expand the node, then click .

In the window for , locate the section.

From the list, choose .

Study 3, Linear Discretization for Mesh Adaptation

Step 1: Frequency Domain, RF Adaptive Mesh

In the window, under click .

In the window for , locate the section.

In the text field, type 0.05.

In the text field, type 20.

Click to expand the section. Select the checkbox.

In the table, enter the following settings:


Plot group	Plot window
Electric Field (emw), Mesh Adaptation	Graphics

Adjust the view, to clearly see the mesh on both the substrate and the boundary toward the PML.

Click the

button in the toolbar.

Click the

button in the toolbar three times.

In the toolbar, click

In the window, follow how the mesh is adapted while solving.

Results

Electric Field (emw), Mesh Adaptation

Notice that the mesh is much denser in the adapted mesh around the patch edges, compared to the original mesh, except where the field strength is low.

Goal-Oriented Termination Expression 3

In the window, click .

This plot shows how the mesh adaptation converges and stops when the increment size is less than the tolerance of 0.02.

Add Study

In the toolbar, click

to open the window.

Go to the window.

Find the subsection. In the tree, select > .

Click the button in the window toolbar.

In the toolbar, click

to close the window.

Study 4, Linear Discretization with Adapted Mesh

In the window for , type Study 4, Linear Discretization with Adapted Mesh in the text field.

Locate the section. Clear the checkbox, as we again will not be saving the field in this study. Therefore, there is no point in generating the default field plots.

Step 1: Adaptive Frequency Sweep

In the window, under click .

In the window for , locate the section.

In the text field, type range(freq_min,100[kHz],freq_max).

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