# Example 13: Boat MOM-GTD

This case explains how to use the Dolph-Chebychev algorithms to calculates the pointing parameters in a bidimensional coaxial feed array, and how to use the resulting radiation pattern in physical applications.

Step 1 Create a new MoM Project.

Open newFASANT and select File - New option.

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

Step 2 Set the simulation parameters as shown.

Select Simulation - Parameters option, set the parameters and save it.

Step 3 Create the array

First, select 'millimeters' on units list on the bar at the bottom of the main window.

Select the surfaces and click on Add.

Then save the feed point.

Use the array command and enter the characteristics of the array.

Step 4 Feed the array

To set the feeding of the array select Source - Antenna Feeding and the following panel will open.

This is the default setting. To use the Dolph-Chebychev algorithm click on Tools - User Function and select the corresponding function. NOTE To use the bidimensional Dolph-Chebychev function it is needed to download both the bidimensional and the unidimensional functions.

A path has been selected by default so the files will be created on the mydatafiles folder in the newFASANT directory.

The next step is generating the text file. To do so click on Tools - Calculator and write the call to the function.

The parameters to set are:
• d1: element spacing of the array in the x-axis in units of lambda.
• N1: L number of array elements of the array in the x-axis.
• R1: relative sidelobe level (in dB) in the x array.
• d2: element spacing of the array in the y-axis in units of lambda.
• N2: number of array elements of the array in the y-axis.
• R2: relative sidelobe level (in dB) in the y array.
• theta: beam angle, in degrees.
• phi: Azimuth angle, in degrees.

In this case, set the parameters as shown. Angles of theta=0º and phi=0º, and a sidelobe level of 50 dB are selected as an example.

A spacing of 0.5 in units of lambdas is selected because is equivalent to a spacing of 2.104 millimeters at 70 GHz.

The text file will be automatically generated in the mydatafiles folder.

Now, apply these results to the array created before by clicking on Source - Antenna Feeding.

The panel shown before will appear. To use the weights and phases calculated with the Dolph-Chebychev algorithm, click on Import.

Select the corresponding file and save the feeding.

Step 5 Solver parameters

Select Solver - Advanced Options and set the parameters as shown.

Step 6 Meshing the geometry model.

Select Mesh - Create Mesh to open the meshing configuration panel and then set the parameters as show the next figure.

Step 7 Execute the simulation.

Select Calculate - Execute option to open simulation panel.

Step 8 Show Results

The radiation cuts can be visualized by clicking on Show Results - Radiation Pattern - View Cuts.

Note that the side lobe level selected earlier must be represented here.

The radiation pattern can be visualized by clicking on Show Results - Radiation Pattern - View 3D Pattern.

Step 9 Rotate the array

In order to obtain the radiation in the desired orientation, rotate the array.

Step 10 Obtain results

Now, mesh and execute the case again. The desired results are as shown.

NOTE to visualize the polar amplitude, click on Show Results - Radiation Pattern - View Cuts and then select Polar Amplitude.

Step 10 Export results

Export these results by clicking on Show Results - Radiation Pattern - Export as DIA File.

Now, save the project and exit it.

Step 11 Create a GTD project

Create a new project, this time with the GTD module.

Step 12 Create the geometry

First, add the boat to the project, by clicking on Geometry - Import.

Select the corresponding .igs file and open it.

Rotate the ship so it is aligned with the radiation direction.

To introduce the desired radiation pattern into the project, click on Antenna - Import DIA File.

Select the .dia file created earlier in the MoM project and open it.

To add the antenna to the project, click on Antenna - Pattern File Antenna - Pattern File Antenna. Add the .dia file and create a dipole antenna with the parameters shown below.

Step 13 Set the simulation parameters as shown.

Select Simulation - Parameters option, set the parameters and save it.

Step 14 Observation directions

Click on Observation Directions.

Step 15 Meshing the geometry model.

Select Meshing - Create Visibility Matrix to open the meshing configuration panel and then set the parameters as show the next figure.

Step 16 Execute the simulation.

Select Calculate - Execute option to open simulation panel.

Step 17 Show Results

To visualize the rays from the antenna, click on Show Results - View Ray.

The radiation cuts can be visualized by clicking on Show Results - Far Field - View Cuts. NOTE to visualize the polar amplitude, click on Polar Amplitude.

Here is a comparison of this example with a project that has the same antenna but without the boat. The blue line represents the array with the boat and the red line is the project without the boat.