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## 15.12. Design of waveguides

### 15.12.1. Example 1: Analysis of a Waveguide with 12 Rotated Slots

This case explains how to create and calculate far-field, radiation pattern, current density, charge density and near field of a 12 Slots Feeding Waveguide.

Step 1: Create a New MOM Project

Open newFASANT and select 'File --> New' option.

Figure: New Panel Project

Select 'MOM' option on the previous figure and start to configure the project.

Step 2: Change the scale to cm.

Figure: Scale settings

Step 3Open the function

Select 'Tools --> User Functions' option on the menu bar and open the function "SlottedWaveguide.java"

Figure: User Function Code

Look at these lines, where you can change the parameters of the waveguide structure

Figure: User Function Code

The parameter "a" represents the width of the guides and it is calculated to be equal to lambdag / 2.

Step 4Configure the parameters of your Project.

Select 'Tools --> Calculator' option on the menu bar and write  "SlottedWaveguide(N,F,angle,slotgap)" on the command line.

N is the number of slots, F is the design frequency value in GHz, angle is the rotation angle of the slots and slot gap is the distance between the slot's center and the meridian of the upper face of the waveguide.

In our case, as we want a 12-slot feeding waveguide: N= 12, F=10 Ghz, angle=0 and slotgap = 0.243953 cm

Although in this example the slots aren't rotated, the user function allows to rotate them in phase and in counter phase alternately.

The script file, called “script_waveguide.nfs”, will be automatically generated in the mydatafiles folder in the newFASANT directory.

Figure: Calculator panel

Step 5: Load the generated Script

The next step is to execute the generated script file. For that, click on Tools – Script - Load and open the script "script_waveguide.nfs".

Figure: Geometry

Step 6: Set Simulation Parameters

Select 'Simulation --> Parameters' option on the menu bar and the following panel appears. Set the parameters as the next figure shows and save it.

Figure: Simulation Parameters panel

Note: The design frequency and the simulation frequency must be the same.

Step 7: Add a port to the waveguide

Step 8: Set the solver parameters.

Click on Solver --> Parameters option on the menu bar. Verify that all the parameters are defined by default, as shown in next figure. Click on Save button before going to next step

Figure: Solver Parameters panel

Select ‘Advanced Options’ and activate Preconditioner as shown.

Step 9: Meshing the geometry model.

Select 'Meshing --> Parameters' to open the meshing configuration panel and then set the parameters as show the next figure.

Because this design requires a high precision, 20 division are set.

Figure: Meshing panel

Step 10Execute the simulation.

Select 'Calculate --> Execute' option to open simulation parameters. Then select the number of processors as the next figure show. In order to obtain the shortest possible time for calculating the results, it is recommended to run the process with the number of physical processors available to the machine.

Then click on 'Execute' button to starting the simulation.

Figure: Execute panel

Step 11Show Results.

To get more information about the graphics panel advanced options (clicking on right button of the mouse over the panel) see Annex 1: Graphics Advanced Options on GUI User Guide.

Select 'Show Results --> Radiation Pattern --> View 3D Pattern' option to show the cuts of the radiation pattern options.

Changing values for step, frequency, magnitude, component or filtering parameters the visualization for the new parameters will be shown.

Selecting other values for the component, step, frequency or cut parameters and clicking on 'Add Series' button a new cut will be added to the selected parameters.

On 'Show Results --> Far Field' menu, other results are present such as 'View Cuts by Step' and 'View Cuts by Frequency' and this option display the values for one selected point for each step or frequency.

On 'Show Results --> Radiation Pattern' menu, other results are present such as 'View Cuts by Step' and 'View Cuts by Frequency' and this option display the values for one selected point for each step or frequency.

Select 'Show Results --> View Currents' option to show the current density.

Figure: Current Density

Changing values for step, frequency, magnitude, component or filtering parameters the visualization for the new parameters will be shown.

If you have selected "S-parameters" on the Simulation Panel now you will have enabled the 'Show Results --> S-Parameters' option.

### 15.12.2. Example 2: Design of an array of slotted waveguides

This case explains how to create an array with 12 upper waveguides and calculate its far-field, radiation pattern, current density, charge density and near field.

Step 1: Create a New MOM Project

Open 'newFASANT' and select 'File --> New' option.

Figure: New Project panel

Select 'MOM' option on the previous figure and start to configure the project.

Step 2: Change the scale to cm.

Figure: Scale settings

Step 3Open the function

Select 'Tools --> User Functions' option on the menu bar and open the function "SlottedWaveguideArray.java"

Figure: User Function Code

Look at these lines, where you can change the parameters of the waveguide structure

Figure: User Function Code

The parameter "a" represents the width of the guides and is calculated to be equal to lambdag / 2 so that for any working frequency the side walls of the upper guides are in contact and there is no gap.

Step 4: Create the geometry of the waveguide array

Select 'Tools --> Calculator' option on the menu bar and write  "SlottedWaveguideArray(N,M,F)".

In our case, as we want a 12-slot feeding waveguide, N= 12,  M=11 and F is the working frequency value in GHz.

The script file, called “script_waveguide.nfs”, will be automatically generated in the mydatafiles folder in the newFASANT directory.

Figure: Calculator panel

So our array will have a feeding waveguide with 12 slots, 12 upper guides with 11 slots each one and the working frequency is 10 GHz.

Step 5: Load the generated Script

The next step is to execute the generated script file. For that, click on Tools – Script - Load and open the script "script_waveguide.nfs".

Figure: Geometry

Step 6: Set Simulation Parameters

Select 'Simulation --> Parameters' option on the menu bar and the following panel appears. Set the parameters as the next figure shows and save it.

Figure: Simulation Parameters panel

If the frequency to which you are going to simulate is equal to the frequency at which the parameters of the array were calculated, the radiation diagram will have the shape of a brush pointing along the z axis. On the other hand slightly varying the frequency of simulation will get the brush to oscillate around the z-axis.

Step 7: Add a port to the feeding waveguide.

Click on the waveguide and Select 'Source --> Waveguides--> Add Waveguide Port' option on the menu bar and add the port.

Step 8: Set the solver parameters.

Click on Solver --> Parameters option on the menu bar. Verify that all the parameters are defined by default, as shown in next figure. Click on Save button before going to next step

Figure: Solver panel

Select ‘Advanced Options’ and activate Preconditioner as shown.

Figure: Main Properties Solver Panel

Figure: Preconditioner Solver Panel

Step 9Meshing the geometry model.

Select 'Meshing --> Parameters' to open the meshing configuration panel and then set the parameters as show the next figure. In order to obtain the shortest possible time for meshing, it is recommended to run the process of meshing with the number of physical processors available to the machine.
As it is a very complicated design requires 20 divisions in the mesh and a high computing capacity

Figure: Meshing Panel

Step 10Execute the simulation.

Select 'Calculate --> Execute' option to open simulation parameters. Then select the number of processors as the next figure show. In order to obtain the shortest possible time for calculating the results, it is recommended to run the process with the number of physical processors available to the machine.

Figure: Execute panel

Then click on 'Execute' button to starting the simulation.

Step 11: Show Results.

To get more information about the graphics panel advanced options (clicking on right button of the mouse over the panel) see Annex 1: Graphics Advanced Options on GUI User Guide.

Select 'Show Results --> Radiation Pattern --> View 3D Pattern' option to show the radiation diagram in three dimensions.