Designing an Axial-Choke Conical Horn Antenna in Antenna Magus


Zoom Image of the Axial corrugated horn antenna

The axial-choke conical horn is a very popular reflector feed as it provides an almost-flat wavefront in the main beam with a sharp roll-off which is ideal for uniform dish illumination with little spillover. In this application note we go through the process of designing an axial-choke conical horn antenna in Antenna Magus. No prior experience in using Antenna Magus is required.

We start by looking at navigation of the Antenna Database and selecting the antenna for design. Then we look at the process of designing the antenna prototype according to certain design specifications using the design options offered. Antenna Magus is then used to estimate performance of our prototype and evaluate the effect that tweaks to the designs have on their performance. A significant feature of Antenna Magus is the capability to export ready-to-run parameterized models of designed antennas for analysis in leading commercial full-wave CEM simulation packages. As a last step we will demonstrate how the designed antenna prototypes can be exported to CEM simulation packages.

Getting to know the UI

If you are unfamiliar with Antenna Magus it is recommended that you briefly familiarize yourself with the basic layout of the UI before continuing with the rest of the application note. A description of the main areas in UI is given below.

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  • Ribbon - Offers Access to commonly used tools and operations. It also allows the user to switch between different modes in the application.
  • Palette - The pallet consist of expanders that generally follow workflow of the application, however, strict adherence to this workflow is not required. The expanders generally consist of parameters and operations.
  • Workspace - Typically displays results and additional information. Here the user is able to view and refine results.
  • Collections - Consists of the users antenna prototypes.

Locating the Axial-Choke Conical Horn Template

Antenna Magus starts up in 'Find mode', where users can explore over 250 antenna templates available in the database and view information on them. If this database is not visible click on the 'Find mode' button on the 'Home' ribbon as shown on the right. Zoom

To find an antenna we enter the name of the antenna or keywords describing it into the search bar. When typing a keyword into the search bar, suggested terms and their definitions according to the Keyword Dictionary will be shown. A Keyword can also be added by selecting it while browsing the dictionary (click on the All Keywords button to start browsing).


Enter the keywords 'corrugated' and 'reflector feed' in the search bar. The list of Antenna Templates in the Find Mode workspace will be reordered and grouped according to the keywords, with the most relevant antennas on top. The axial-choke conical horn template will be in the top group for these keywords.

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An animated rotation of the 3D image of the axial-choke conical horn antenna that aids in visualising the structure of the antenna from all sides can be triggered by clicking on the thumbnail image.

Learning about the Axial-Choke Conical Horn antenna

This antenna can be seen as a small aperture horn with corrugations placed in the flanges to design for a wide beam width with good pattern symmetry and low cross-polarisation. By clicking on the info button that appears when hovering over the template the Information Browser will be opened in a separate window. (Note: the 'Add to Info Browser' and 'Open Info Browser' button on the 'Home' ribbon can also be used for this). In the Information Browser, information about the antenna can be viewed and compared to information about other antennas. Below is the comparison of the Axial-choke horn to the Scrimp horn. The compare view can be opened by loading two antennas into the information browser and then clicking on the 'New Comparison' button.

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Once finished revising the background information; close the information browser, or switch back to the main Antenna Magus window to start the design process.

Designing the Axial-Choke Conical Horn antenna

In the Antenna Database click on the 'Add' button of the axial-choke conical horn, this will add a new antenna prototype to the to the user collection. This collection, displayed at the bottom of the main window, is stored and will reload when the application is restarted. To enter the design mode click on the 'Design' button of the prototype's thumbnail in the user collection. Start the design by giving it an appropriate name, to do this click on the title of the design and rename it from 'Design 1' to 'Axial-Choke Conical Horn Design 1'. There are two design objective options offered by this template. The first option caters for the design based only on the required operating frequency. The second option allows the gain and degree of beam flatness to be controlled in addition to the operating frequency.

Design for operating frequency

To design the antenna by only specifying the operating frequency, select the 'operating frequency' option in the 'Design for:' drop down menu in the palette. An input field is now available to enter the desired centre frequency (f0). By hovering the mouse over the input field the input range will be displayed. For this template the input frequency has to be within 1GHz and 100 GHz range. If the input is invalid or out of range a warning or error indicator will be shown in the field. A hint indication why the input is not valid will be displayed when the mouse hovers over the indicator icon.

Zoom Once the desired centre frequency is selected (use 50 GHz for this example) and entered in the input field, click on the 'Design' button. This will calculate the physical parameters of the prototype to adhere to the centre frequency as design requirement. These physical parameters are visible in the 'Parameters' expander in the palette and correlate with the physical parameters shown in the 'Sketches' pane in the workspace.

Click on the 'Estimated Performance' tab once the estimation has finished. Here the radiation pattern can be reviewed in the form of a 2D as well as a 3D graph.
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The values of parameters can be individually adjusted or 'tweaked' using the sliders or directly entering values into the palette fields if needed. For this example we will leave them unaltered and click on 'Estimate Performance'. This will calculate the radiation patterns of the prototype with the current parameters. The calculation is processor intensive and may take a few minutes complete. The calculated radiation pattern can be reviewed in the form of a 2D as well as a 3D graph.



Double click on the 2D plot to expand the view with additional information.
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The data representation of the plots can be changed by clicking on the 'Change representation' button on the 'Format' tab ribbon. A selection of representations available for this plot will be displayed. Switch between these representations to view their effect. Zoom

Tweaking the Design

If external constraints dictate limitations on the physical design they can be incorporated and estimated in Antenna Magus. Go back to the 'Sketches and Design Guidelines' tab in the 'Design Mode' workspace. Suppose a design constraint limits the diameter of the antenna design then the diameter can be reduced by reducing the number of chokes (N). Click on the 'New Tweak' button. Rename the tweak to 'Tweak - Reduced Chokes' and Change the value of N from 10 to 2. The model preview will be updated reflecting the change in the number of chokes parameter. A reduction in the antenna radius is also visible in the updated model view. Now click on the 'Estimate Performance' button to calculate the performance of the tweaked design.

Zoom Once the estimation has completed, switch to the 'Estimated Performance' tab. Here the new results will be displayed on the same graph where it can be compared with the original performance as shown on the 'Radiation Pattern' plot. The comparison shows that spill over is greatly increased as the number of chokes are reduced, illustrating the benefit offered by the chokes.

Add Gain, and Beam Flatness specifications to the design

Antenna Magus also offers an additional design method for this antenna which takes gain, operating frequency and beam flatness into account. Click on the New Design button in the Design Objective expander in the palette and select 'gain and beam flatness at operating frequency'. This design mode allows us to take these criteria into account. Change the name of this design to "Axial-Choke Conical Horn Design 2". Leave the operating frequency at 50 GHz and set the gain to 15 dBi and the beam flatness to 'low'. Click on 'design' and 'estimate performance' again to simulate the new design.

Zoom Once the simulation has completed navigate to the 'Estimated performance' tab. Here the new design's performance can be compared to that of the previous. An increased gain and reduced beam width is clearly visible in the polar radiation plot.

Exporting CEM models of designs to FEKO, CST Microwave Studio and Champ

Antenna Magus allows of the export of fully parametric, ready-to-run models to FEKO, CST and Champ. The advantage of the models being parametric is that they can be easily edited in these packages. Since the models are "ready-to-run" any changes can be simulated in the respective packages without the need to specify mesh properties, ports, far field locations boundary conditions etc. Zoom



To open the export view select the design to be exported in the 'Designs and Tweaks' window and click on 'Export Mode' in the 'Home' ribbon.
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Exporting to CHAMP
Exporting to CST
Exporting to FEKO

[Note: A licenced version of the chosen CEM tool is required to open and work with the models exported by Antenna Magus, and will be needed to complete the steps illustrated below]

Exporting to CHAMP

Select the 'CHAMP' tab in the Export View of Antenna Magus. Review the parameters and click on the 'Export Model' button. Ensure that the file type is set to "Champ Model", name the file "Axial-Choke Conical Horn Design 1.zip" and save it to an appropriate location. Minimize Antenna Magus and unzip the contents of the exported zip file. Open the "antennaCHAMP.champ" file. The Antenna Magus prototype is now open for editing and analysis in CHAMP.
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The parameters of the antenna can be edited in table located on the right-hand side of the screen. Locate the 'Number of Axial Slots' parameter and change it to observe the model changes. To simulate the antenna click on the 'Analysis' drop down menu and select 'Analyse Horn...'. Click 'OK' on the popup dialog and click 'OK' on the result dialog when analysis has completed. Now click on the 'Results' button on the left-hand navigation pane to view the results.
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Exporting to CST

Select the 'CST MICROWAVE STUDIO' tab in the Export View of Antenna Magus. Review the parameters and click on the 'Export Model' button. Name the file "Axial-Choke Conical Horn Design 1.cst" and save it to a convenient location. Minimize Antenna Magus and open the exported file. The Antenna Magus prototype is now open for editing and simulation in CST MWS.
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To edit the parameters of the model edit the values in the table below the model view. Change the 'num_chokes' parameter's value and press F7 to view the effect of a parameter change. To run the simulation in CST click on the 'Solve' drop down menu and then on 'Time Domain Solver...'. Inspect the parameters and click on 'Start' to run the simulation. Once the simulation has completed expand the Farfields tree node on the navigation pane. Here the simulation results can be reviewed.
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Exporting to FEKO

Select the FEKO tab in the Export View of Antenna Magus. Review the parameters and click on the 'Export Model' button. Ensure that the file type is set to "CADFEKO model", name the file "Axial-Choke Conical Horn Design 1.cfx" and save it to a convenient location. Minimize Antenna Magus and open the exported file. The Antenna Magus prototype is now open for editing and simulation in CADFEKO.
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On the 'Construct' ribbon click on the Variable drop down and select multiple variables. This opens the 'Modify Multiple Variables' window. Here the parameters designed in Antenna Magus can be edited. Click on the 'num_chokes' variable and change the value and click 'OK'. The model in CADFEKO is now updated to have the corresponding number of chokes. Zoom

To simulate the antenna in FEKO a mesh has to be constructed first. Select the 'Mesh' tab and click on 'Create Mesh', this will open the 'Create mesh' menu. Review the mesh settings and click on the 'Mesh' button, this will create the mesh for the FEKO solver. Once the mesh is created, go to the 'Solve/Run' tab and click on 'FEKO solver' to run the simulation (The solver takes a few minutes to run). When the solver has finished, click on the 'POSTFEKO' button on the 'Solve/Run' tab. Here the results of the solver can be viewed.
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Simulation Comparison

The results displayed bellow compare the total gain radiation patterns calculated by FEKO, CST MICROWAVE STUDIO and TICRA CHAMP.
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Conclusion

This application note shows that we can design and Axial choke horn and compare its performance in three commercial full wave packages in a short time. For further reading view other Application Notes available here.

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