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.
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.
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.
An animated rotation of the 3D image of the axial-choke conical horn antenna that aids in visualizing 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-polarization. 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.
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 center 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.
Once the desired center 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 center 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.
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.
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.
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.
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 designAntenna 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.
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 CST Studio Suite
Antenna Magus allows of the export of fully parametric, ready-to-run models to CST Studio Suite. 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.
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.
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 Studio Suite.
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 Studio Suite, 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.
This application note shows that, in only a short time, we can design and Axial choke horn and examine its performance in CST Studio Suite.