|
|
| Line 1: |
Line 1: |
| − | {{projectinfo|Tutorial| Designing a Yagi-Uda Dipole Array|WMOM114.png|In this project, a Yagi-Uda dipole array is built using array objects and will be analyzed using the Wire MoM solver.|
| |
| | | | |
| − | *[[CubeCAD]]
| |
| − | *Array objects
| |
| − | *Gap Sources
| |
| − | *Mesh Resolution
| |
| − | *Adaptive sweep
| |
| − | |All versions|{{download|http://www.emagtech.com|EM.Libera Lesson 3|[[EM.Cube]] 14.9}} }}
| |
| − |
| |
| − | ===Objective:===
| |
| − |
| |
| − | To construct a Yagi-Uda dipole antenna array in [[EM.Cube]]’s [[MoM3D Module]], analyze it using the Wire MoM solver and modify its number of director elements.
| |
| − |
| |
| − | ===What You Will Learn:===
| |
| − |
| |
| − | A multi-element Yagi-Uda antenna array will be analyzed in the this tutorial lesson. You will learn how to build and modify array objects.
| |
| − |
| |
| − | ==Getting Started==
| |
| − |
| |
| − | Open the [[EM.Cube]] application and switch to [[MoM3D Module]]. Start a new project with the following attributes:
| |
| − |
| |
| − | #Name: [[WMOMLesson3]]
| |
| − | #Length Units: mm
| |
| − | #Frequency Units: GHz
| |
| − | #Center Frequency: 2.4
| |
| − | #Bandwidth: 1.0
| |
| − |
| |
| − | [[Image:WMOM100.png|thumb|500px|The Yagi-Uda array schematic.]]
| |
| − | A Yagi-Uda array is often made of an exciter element, a reflector element and several director elements. The lengths of all the elements vary around a half wavelength. The following table shows these lengths and spacing of a typical design:
| |
| − |
| |
| − | {| class="wikitable"
| |
| − | |-
| |
| − | ! Element !! Length !! Distance from Exciter
| |
| − | |-
| |
| − | | Exciter || 0.47λ<sub>0</sub> || 0
| |
| − | |-
| |
| − | | Reflector || 0.5λ<sub>0</sub> || 0.25λ<sub>0</sub>
| |
| − | |-
| |
| − | | Director || 0.406λ<sub>0</sub> || 0.34λ<sub>0</sub>
| |
| − | |-
| |
| − | |}
| |
| − |
| |
| − | In the above design, the spacing between the director elements is uniform and equal to 0.34λ<sub>0</sub>. The radius of all wires is 0.003λ<sub>0</sub>.
| |
| − |
| |
| − | ==Drawing the Wires==
| |
| − |
| |
| − | In this project, f<sub>0</sub> = 2.4GHz. Therefore, the free-space wavelength is λ<sub>0</sub> = 125mm. Draw the three vertical lines with the given lengths and local coordinate systems (LCS). Remember that the LCS of a line object is established at one end of the line. Therefore, the centers of the following lines must lie on the X-axis, which is the array axis.
| |
| − |
| |
| − |
| |
| − | [[Image:WMOM101.png|thumb|500px|The drawn Yagi-Uda array structure.]]
| |
| − | {| class="wikitable"
| |
| − | |-
| |
| − | ! Line Object !! Length !! LCS Coordinates
| |
| − | |-
| |
| − | | Line_1 || 58.75mm || (0, 0, -29.375mm)
| |
| − | |-
| |
| − | | Line_2 || 62.50mm || (-31.25mm, 0, -31.25mm)
| |
| − | |-
| |
| − | | Line_3 || 50.75mm || (42.50mm, 0, -25.375mm)
| |
| − | |-
| |
| − | |}
| |
| − |
| |
| − | Next, select the director line object (Line_3) and use the Array Tool to create an array object with the following [[parameters]]:
| |
| − |
| |
| − | {| class="wikitable"
| |
| − | |-
| |
| − | ! Direction !! Number of Elements !! Element Spacing
| |
| − | |-
| |
| − | | X || 5 || 42.mm
| |
| − | |-
| |
| − | | Y || 1 || 0
| |
| − | |-
| |
| − | | Z || 1 || 0
| |
| − | |-
| |
| − | |}
| |
| − |
| |
| − | As you can see from the opposite figure, your structure should now have a total of 7 vertical dipoles.
| |
| − |
| |
| − | ==Defining the Source and Observables==
| |
| − |
| |
| − | [[Image:WMOM102.png|thumb|500px|The drawn Yagi-Uda array structure.]]
| |
| − | Define a gap source and place it at the center of the exciter element Line_1. Choose the default values of the gap [[parameters]]. Then, define a current distribution observable as well as a far fields observable. In the Radiation Pattern dialog of the far fields observable, set the angle increments to 1 degree for both "Theta" and "Phi" spherical observation angles. Finally, define a default "Port Definition" observable. You will be interested in examining the frequency response of the Yagi-Uda antenna array.
| |
| − |
| |
| − | ==A Study of Mesh Density and Numerical Convergence==
| |
| − |
| |
| − | Open the Mesh Settings dialog and note that the default mesh density is 10 samples per wavelength. Run a single-frequency Wire MoM analysis of the Yagi-Uda array. Write down the values for return loss (|S<sub>11</sub>| in dB), input impedance (Z<sub>11</sub>), maximum current density and directivity. Then, go back to the Mesh Settings dialog and change the mesh density to 30 samples per wavelength. Run another Wire MoM analysis and write down the values of the observables. Repeat this procedure for mesh density values of 50, 100 and 150 samples per wavelength. The table below shows the results:
| |
| − |
| |
| − |
| |
| − | {| class="wikitable"
| |
| − | |-
| |
| − | ! Mesh Density !! Linear System Size !! Return Loss !! Input Impedance !! Maximum Current Density !! Directivity
| |
| − | |-
| |
| − | | 10 || 23 || -0.831dB || 47.828 -212.969j Ω || 2.43A/m || 4.715
| |
| − | |-
| |
| − | | 30 || 82 || -9.509dB || 64.694 -37.624j Ω || 7.05A/m || 5.665
| |
| − | |-
| |
| − | | 50 || 141 || -14.444dB || 66.009 -15.357j Ω || 7.83A/m || 6.353
| |
| − | |-
| |
| − | | 100 || 295 || -17.213dB || 65.939 -1.146j Ω || 8.04A/m || 7.114
| |
| − | |-
| |
| − | | 150 || 443 || -17.175dB || 65.973 +1.627j Ω || 8.04A/m || 7.321
| |
| − | |-
| |
| − | | 200 || 592 || -17.061dB || 66.05 +2.741j Ω || 8.02A/m || 7.393
| |
| − | |-
| |
| − | | 250 || 745 || -16.98dB || 66.084 +3.409j Ω || 8.02A/m || 7.421
| |
| − | |-
| |
| − | | 300 || 894 || -16.941dB || 66.120 +3.618j Ω || 8.01A/m || 7.432
| |
| − | |-
| |
| − | |}
| |
| − |
| |
| − | As you can clearly see from the above results, the Wire MoM solution does not converge at lower mesh densities. You need to increase the mesh density to 150 cells per wavelength to get reasonably accurate results. The figures below show the current distribution and radiation pattern plots of the array for a mesh density of 150 cells per wavelength.
| |
| − |
| |
| − | <table>
| |
| − | <tr>
| |
| − | <td>
| |
| − | [[Image:WMOM103.png|thumb|400px|The current distribution on the Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | <td>
| |
| − | [[Image:WMOM104.png|thumb|400px|The 3D far field radiation pattern of the Yagi-Uda antenna array with 5 directors.]]
| |
| − | </td>
| |
| − | </tr>
| |
| − | </table>
| |
| − |
| |
| − | <table>
| |
| − | <tr>
| |
| − | <td>
| |
| − | [[Image:WMOM105.png|thumb|400px|The 2D Cartesian XY-plane radiation pattern of the Yagi-Uda antenna array with 5 directors.]]
| |
| − | </td>
| |
| − | <td>
| |
| − | [[Image:WMOM106.png|thumb|400px|The 2D polar XY-plane radiation pattern of the Yagi-Uda antenna array with 5 directors.]]
| |
| − | </td>
| |
| − | </tr>
| |
| − | <tr>
| |
| − | <td>
| |
| − | [[Image:WMOM107.png|thumb|400px|The 2D Cartesian ZX-plane radiation pattern of the Yagi-Uda antenna array with 5 directors.]]
| |
| − | </td>
| |
| − | <td>
| |
| − | [[Image:WMOM108.png|thumb|400px|The 2D polar ZX-plane radiation pattern of the Yagi-Uda antenna array with 5 directors.]]
| |
| − | </td>
| |
| − | </tr>
| |
| − | </table>
| |
| − |
| |
| − | [[Image:WMOM109.png|thumb|400px|The return loss (|S<sub>11</sub>|) of the Yagi-Uda antenna array with 5 directors.]]
| |
| − | Next, you will run a frequency sweep of the Yagi-Uda antenna array to see its frequency behavior. For this part of the project, you may want to delete the far field observable because calculating the radiation patterns at an angular resolution of 1 degree for both theta and phi may take a considerable amount of time at each sweep step. Open the Run Dialog and select "Frequency Sweep" option for Simulation Mode. In the Frequency Settings dialog, set the start and end frequencies to 1.9GHz and 2.9GHz, respectively. Select the "Adaptive" option for the Frequency Sweep Type and accept all the default parameter of the adaptive sweep. Run the sweep simulation. After the completion of the sweep, open the Data Manager and plot the file "S11_RationalFit.CPX" in EM.Grid.
| |
| − |
| |
| − |
| |
| − | ==Increasing the Number of Directors==
| |
| − |
| |
| − | In this part of the tutorial lesson, you will increase the number of the director elements and see its effect on the array characteristics. Open the array properties dialog by either double-clicking on the array object in the project workspace or by right-clicking on its name in the Navigation Tree and selecting <b>Properties...</b> from the contextual menu. Change the value of "Element Count" along the X direction from 5 to 9 and keep the "Element Spacing" in that direction intact. This will increase the total number of the Yagi-Uda array elements to 11. Run a new single-frequency Wire MoM analysis of the expanded array. Make sure to restore the far fields observable if you deleted in during the frequency sweep in the previous part.
| |
| − |
| |
| − | <table>
| |
| − | <tr>
| |
| − | <td>
| |
| − | [[Image:WMOM110.png|thumb|400px|The 11-element Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | </tr>
| |
| − | </table>
| |
| − |
| |
| − | <table>
| |
| − | <tr>
| |
| − | <td>
| |
| − | [[Image:WMOM111.png|thumb|540px|The current distribution on the 11-element Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | <td>
| |
| − | [[Image:WMOM112.png|thumb|540px|The 3D far field radiation pattern of the 11-element Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | </tr>
| |
| − | </table>
| |
| − |
| |
| − | As you can see from the above radiation pattern plot, the directivity of the array increases from 7.4 to 9.3 when you increase the number of directors from 5 to 9. The array directivity can be further increased by adding yet more director elements. Open the array properties dialog and change the value of "Element Count" along the X direction from 9 to 13 with the same element spacing. This will increase the total number of the Yagi-Uda array elements to 15. Run a new single-frequency Wire MoM analysis of the 15-element array. The figures below show the simulation results. As you can see, the directivity has now increased to 11.2. From the current distribution plot, one can conclude that the addition of the new director elements make the end-fire array's radiation pattern more directional, however, it does not affect the current distribution on the exciter element. Therefore, you should not expect the port characteristics of the antenna to change sizably as you increase the number of directors.
| |
| − |
| |
| − | <table>
| |
| − | <tr>
| |
| − | <td>
| |
| − | [[Image:WMOM113.png|thumb|540px|The current distribution on the 15-element Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | <td>
| |
| − | [[Image:WMOM114.png|thumb|540px|The 3D far field radiation pattern of the 15-element Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | </tr>
| |
| − | </table>
| |
| − |
| |
| − | <table>
| |
| − | <tr>
| |
| − | <td>
| |
| − | [[Image:WMOM115.png|thumb|400px|The 2D Cartesian XY-plane radiation pattern of the 15-element Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | <td>
| |
| − | [[Image:WMOM116.png|thumb|400px|The 2D polar XY-plane radiation pattern of the 15-element Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | </tr>
| |
| − | <tr>
| |
| − | <td>
| |
| − | [[Image:WMOM117.png|thumb|400px|The 2D Cartesian ZX-plane radiation pattern of the 15-element Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | <td>
| |
| − | [[Image:WMOM118.png|thumb|400px|The 2D polar ZX-plane radiation pattern of the 15-element Yagi-Uda antenna array.]]
| |
| − | </td>
| |
| − | </tr>
| |
| − | </table>
| |
| − |
| |
| − | {{EMCUBE directory}}
| |
| − |
| |
| − | [[EM.Cube | Back to EM.Cube Wiki Main Page]]
| |
