Antennas Lab 2

LAB 2. Antenna Array

This laboratory is intended to show you how to create, simulate, and analyze a Waveguide array antenna using the Ansoft HFSS Design Environment. A WavePort excitation will be used for the feed PMLs (Perfectly Matched Layers) and for the radiation load Master/Slave boundary conditions will be used to create the array. Arrays can be designed to radiate in either broadside i.e. radiation perpendicular to array orientation or end fire i.e. radiation in the same direction as the array. We will focus on end fire arrays.

1 Starting HFSS

Double click on the HFSS 9.2 icon on the Windows Desktop

2 Creating the Project First launch the HFSS Simulator. From the Project Manager window right-click the project file and select Save As from the sub menu. Name the file “AntennaArray” and Click Save. To begin working with geometries you must insert an HFSS design. Right-Click the project file and select Insert → Insert HFSS Design from the menu.

3 Setting Tool Options

Note: In order to follow the steps outlined in this example, verify that the following tool options are set. Select the menu item Tools → Options → HFSS Options. Click the General tab

EE 442 Antennas and Wave Propagation

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Select the menu item Tools → Options → Modeler Options. Click the Operation tab

Click the Drawing tab

4 Set Model Units


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To set the units select the menu item 3D Modeler → Units. Select Units: in

5 Set Default Material

Using the Modeler Materials toolbar, make sure that vacuum is the default material

6 Create Waveguide

We will start by creating the waveguide using the Draw Box button from the toolbar.


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Double click on CreateBox to get Command window. Enter the box position

Double click on Box1 to get Attribute window. For the Value of Name type: waveguide Click the OK button


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To fit the view: Select the menu item View → Fit All → Active View or press the CTRL+D keys


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7 Create Airbox To create the airbox select the menu item Draw → Box. Enter the box position

Select the Attribute tab double clicking the Box1. For the Value of Name type: airbox. Click the OK

button

To fit the view: Select the menu item View → Fit All → Active View


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To select the proper face of the airbox select the menu item Edit→ Select →Faces

Graphically pick the top face of the airbox that was just created.


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To assign the PML boundary select the menu item HFSS → Boundaries → PML Setup Wizard

Select Create PML Cover Objects on Selected Faces. Uniform Layer Thickness: 0.2in, click the Next button


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Select: PML Objects accept Free Radiation. Min Frequency: 9 GHz. Minimum Radiating Distance: 1in. Click the Next button


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Review settings on the PML Setup Wizard: Summary page. Click the Finish button

8 Make the PML object visible


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By default, the PML wizard will turn off visibility of the PML object once it is created. We want to turn it back on again. Select the menu item View → Active View Visiblility. Check the box next to PML_airbox1. Click Done.

9 Create the Master/Slave boundary objects


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To set the grid plane: Select the menu item Modeler → Grid Plane→ YZ or

To draw the first Master/Slave rectangle select the menu item Draw → Rectangle

Enter the box position

To set the name: Select the Attribute tab. For the Value of Name type: Master1 Click the OK button.


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To set the grid plane select the menu item Modeler → Grid Plane → XZ

To draw the second Master/Slave rectangle select the menu item Draw → Rectangle. Enter the box position

To set the name select the Attribute tab. For the Value of Name type: Master2.


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Select the object, Master1. Select the menu item Edit → Duplicate → Along Line

Enter the start position of the duplicate Vector

Enter the end point of the duplicate vector


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When the dialog box pops up requesting the total number of copies, change the value to 2, Press the OK button. Select the object, Master2. Select the menu item Edit → Duplicate → Along Line

Enter the start position of the duplicate

Enter the end point of the duplicate vector


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10 Change Slave boundary names To change the duplicated master boundary to slave boundary Select the objects named: master1_1. Double click for Attribute dialog. Change the Name master1_1 to Slave1.

Select the objects named: master2_1. Double click for Attribute dialog. Change the Name master2_1 to Slave2.


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To create a Master boundary Select the objects named: master1. Select the menu item HFSS →Boundaries → Assign → Master

Name: Master1.Coordinate System: U Vector: click Undefined pulldown and choose New Vector

Using the coordinate entry fields, enter the start position

Using the coordinate entry fields, enter the stop position of the vector


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For the V vector, check the Reverse Direction box

Repeat the process for Master2


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Using the coordinate entry fields, enter the positions


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To create a Slave boundary Select the objects named: Slave1. Select the menu item HFSS → Boundaries → Assign → Slave

Name: Slave1. Master Boundary: click on Undefined pulldown and select Master1 Coordinate System: U Vector: click Undefined pulldown



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Make sure that Use Scan Angles To Calculate Phase Delay is Checked. For Phi, enter 0 deg. For Theta, enter a variable name theta_scan, and hit Enter. For the Add Variable dialog, enter 30 deg for theta_scan

Repeat the process for Slave2 Select the objects named: Slave2. Select the menu item HFSS → Boundaries → Assign → Slave


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Name: Slave2. Master Boundary: click on Undefined pulldown and select Master2. Coordinate System: U Vector: click Undefined pulldown


Choose Next and Finish.

11 Assign Impedance Boundary To create the impedance boundary on the PML object: Select the menu item Edit → Select → Faces. Graphically pick the top face of the PML object


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Select the menu item: HFSS → Boundaries → Assign → Impedance


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Name: TopLoad. Resistance: 377*cos(theta_scan). Reactance: 0

To assign waveport to waveguide object select the menu item Edit → Select → By Name


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Select Face dialog: Select the object waveguide from the left column. Select different FaceIDs until the bottom face of the waveguide is highlighted. Click OK

Select the menu item HFSS → Excitation → Assign → WavePort. Name: p1. Click Next → Next → Finish.


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12 Analysis Setup To create an analysis setup, select the menu item HFSS → Analysis Setup → Add Solution Setup Solution Setup Window: Click the General tab: Solution Frequency: 9.25 GHz. Maximum Number of Passes: 5. Maximum Delta S: 0.0001. Click the OK button

13 Analyze To validate the model select the menu item HFSS → Validation Check. Note: To view any errors or warning messages, use the Message Manager

To start the solution process: Select the menu item Setup1 → Analyze


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15 Create Reports

After completion of the analysis, we will create a report to display both the antenna parameters and also the radiation pattern. HFSS has the ability to compute antenna parameters automatically. In order to produce the calculations, the user must define an infinite sphere for far field calculations. Right-click the Radiation icon in the project manager window and select Insert Far Field Setup → Infinite Sphere.

Choose Phi: (Start: 0, Stop: 360,Step Size: 10), Theta: (Start: 0, Stop: 360, Step Size: 10). Click the OK

button. Right-click Infinite Sphere1 → Compute Antenna Parameters... from the project explorer as

shown

Select all defaults and results are displayed as follows:


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Antenna elements can be arranged to form antenna array. Each antenna exhibits a specific radiation pattern. When combined with several other antenna elements in an array, however, the overall radiation pattern of an antenna changes. To plot radiation pattern select the menu item Results → Create Far Field Report → 3D Polar Plot.


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Enter the following:

Polar Plot is displayed below

Antenna arrays do not have a symmetry in the radiation pattern. These antennas typically have a single

peak direction in the radiation pattern; this is the direction where the bulk of the radiated power travels.


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The elevation plane pattern is formed by slicing the 3D pattern through an orthogonal plane (either the

x-z plane or the y-z plane). To get the elevation plane pattern select the menu item Results → Create Far

Field Report → Radiation Pattern.


Radiation pattern is displayed below


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Radiation plot of most antennas shows a pattern of maxima or "lobes" at various angles, separated by

"nulls" at which the radiation goes to zero. In a directive antenna in which the objective is to direct the

radio waves in one particular direction, the lobe in that direction is larger than the others; this is called

the "main lobe". The other lobes, representing unwanted radiation in other directions, are called "side

lobes". In this pattern, because of the main lobe, most of the radiation is in the first and second

quadrants.

Again, the azimuth plane pattern is formed by slicing the 3D pattern through the horizontal plane (the x-y plane). Select the menu item Results → Create Far Field Report → Radiation Pattern.


http://en.wikipedia.org/wiki/Null_%28radio%29

http://en.wikipedia.org/wiki/Directional_antenna

http://en.wikipedia.org/wiki/Main_lobe

http://en.wikipedia.org/wiki/Side_lobe

http://en.wikipedia.org/wiki/Side_lobe


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Radiation pattern is displayed below

As expected, the pattern is not completely circular.

LAB2: REPORT

The radiation pattern can change dramatically depending upon frequency. Antennas are designed for

a particular frequency. For the report plot the 3D polar, azimuthal and elevation patterns for the

frequency of 15 and 7 GHz.

Antennas Lab 2

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