COMSOL 6.3 - H-Bend Waveguide 2D

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H-Bend Waveguide 2D

This example is a 2D version of H-Bend Waveguide 3D, which shows how to model a bending rectangular waveguide for microwaves. For a general introduction, see the model H-Bend Waveguide 3D.

The dimensions of the waveguide and the frequency range used in this example are such that TE10 is the single propagating mode. In this mode, if the bend is in the xy-plane, the electric field only has a z-component, which furthermore is independent of the z-coordinate. This makes it possible to set up and solve the model in a 2D geometry.

Model Definition

The considered geometry is an xy-plane cross section of the 3D geometry, as seen in Figure 1. This figure also sums up the material and boundary settings, which are the same as in the 3D model. The main advantage with setting up the model in 2D is that it solves much faster and uses less memory. As a consequence, this version of the example does not stress the need to adapt the mesh to the wavelength, but simply lets you apply a mesh that is more than fine enough.

Figure 1: The geometry of the example.

The examples also shows the usage of frequency domain source sweep study that solves for fast port sweep. This study step helps solve a frequency domain study that is sweeping among ports and lumped ports calculating a full S-parameter matrix.

Results and Discussion

Figure 2 shows the norm of the electric field at one of the frequencies where the bend has a resonance. The absence of a wave pattern in the input section indicates that the transmission is nearly perfect.

Figure 2: The electric field norm at a frequency of 4.225 GHz.

Figure 3 shows the S-parameters in a dB scale. The result agrees very well with that of the 3D model. The h-band waveguide is passive and reciprocal and the full S-parameter matrix computed at 5.1 GHz is symmetric.

Figure 3: The S-parameters, in a dB scale, as functions of the frequency.

RF_Module/Transmission_Lines_and_Waveguides/h_bend_waveguide_2d

Modeling Instructions

From the menu, choose .

In the window, click

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In the window, click

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In the tree, select > .

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In the tree, select > .

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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.

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In the window, under click .

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In the window for , locate the section.

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In the text field, type range(4[GHz],25[MHz],5.2[GHz]).

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In the toolbar, click

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In the window for , locate the section.

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In the text field, type 0.08.

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In the toolbar, click

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In the window for , locate the section.

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In the text field, type 0.04.

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In the toolbar, click

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In the window for , locate the section.

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In the text field, type 0.08.

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Locate the section. In the text field, type -0.08.

Compose 1 (co1)

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In the toolbar, click

and choose .

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Click in the window and then press Ctrl+A to select all objects.

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In the window for , locate the section.

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In the text field, type sq1*(c1-c2).

Rectangle 1 (r1)

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In the toolbar, click

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In the window for , locate the section.

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In the text field, type 0.04.

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In the text field, type 0.1.

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Locate the section. In the text field, type 0.04.

Rectangle 2 (r2)

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In the toolbar, click

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In the window for , locate the section.

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In the text field, type 0.1.

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In the text field, type 0.04.

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Locate the section. In the text field, type -0.1.

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In the text field, type -0.08.

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button in the toolbar.

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In the window, under right-click and choose .

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

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Select Domains 1 and 3 only.

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Click to expand the section. In the tree, select > > .

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


Property	Variable	Value	Unit	Property group
Refractive index, real part	n_iso ; nii = n_iso, nij = 0	1	1	Refractive index

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Right-click and choose .

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In the window for , type Silica Glass in the text field.

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Select Domain 2 only.

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Click to expand the section. In the tree, select > > .

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


Property	Variable	Value	Unit	Property group
Refractive index, real part	n_iso ; nii = n_iso, nij = 0	1.44	1	Refractive index

Electromagnetic Waves, Frequency Domain (emw)

With TE waves, only the z component of the electric field needs to be solved for.

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In the window, under click .

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In the window for , locate the section.

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From the list, choose .

Wave Equation, Electric 1

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In the window, under > click .

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In the window for , locate the section.

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From the list, choose .

The default boundary condition is perfect electric conductor, which is fine for all exterior boundaries except the ports. The software automatically imposes continuity on interior boundaries.

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In the toolbar, click

and choose .

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Select Boundary 1 only.

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In the window for , locate the section.

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From the list, choose .

For the first port, wave excitation is by default.

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In the toolbar, click

and choose .

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Select Boundary 7 only.

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In the window for , locate the section.

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From the list, choose .

In the window, under right-click and choose .

In the toolbar, click

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Electric Field (emw)

The default plot shows the norm of the electric field for the highest frequency, 5.2 GHz. To verify that the solution resembles the 3D version, try plotting a frequency where you expect a transmission peak.

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In the window for , locate the section.

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From the list, choose .

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In the toolbar, click

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Finally, plot the S-parameters.

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In the window, expand the > node, then click .

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In the window for , click to expand the section.

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Find the subsection. From the list, choose .

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From the list, choose .

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In the toolbar, click

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Smith Plot (emw)

In the window, under click .

Next, add a study step to solve a frequency domain study sweeping over ports to extract a full S-parameter matrix.

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In the toolbar, click

to open the window.

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Go to the window.

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Find the subsection. In the tree, select > .

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Click the button in the window toolbar.

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In the toolbar, click

to close the window.

Step 1: Frequency Domain Source Sweep

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In the window for , locate the section.

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In the text field, type 5.1[GHz].

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In the toolbar, click

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S-parameter (emw)

Review the evaluated full S-parameter matrix. Since the device is passive and reciprocal, the computed matrix is also symmetric.