CST – Computer Simulation Technology

An Antenna Magus Design Case Study 11 GHz Reflector Antenna Feed with Dual Polarization

All antenna engineers are familiar with a number of antennas. For some it is only a handful, while others seem to have unlimited knowledge of different antenna types and an in depth understanding of the underlying physics that makes them work. Realistically, no single person can know everything about antennas, but it does seem that hands-on experience is probably the most valuable commodity in the field of antenna design. When faced with new design requirements, most engineers will start with antenna topologies that they are familiar with.

Antenna Magus has revolutionized this first step in the antenna design process by broadening the scope of possible antennas that would be considered during the initial phase of design.

Let's look at a typical case where an antenna engineer or consultant needs to design an antenna for a specific system or application. Assume the client supplied the following specifications:...

Design a feed for a reflector with F/D of 0.6
Dish diameter: 400mm
Frequency: 11 GHz
Total gain: 25 dBi
Feed antenna -10 dB beamwidth: 80 degrees
Dual linear polarization

The most common workflow would start by setting up a Specification with everything that can be specified, and selecting appropriate suggested keywords, or adding them directly from the keyword dictionary. For this example, the engineer may enter "reflector feed" and "dual polarization capable". The selection of potentially suitable antennas returned using this Specification in Find Mode is shown below (note that only specifications relevant to the feed antenna have been specified):

Reflector feed antenna options Reflector feed antenna options.

Without any detailed understanding of any of these antennas, the engineer can use the Quick Summary Table in Find Mode, or the complete Information Document in the Information Browser to gain a very good overview of each antenna. These Information Documents outline basic specifications and highlight advantages and disadvantages of the antennas that might be worth considering for the design. The three antennas that will be investigated for this design are shown below:

Reflector feed antenna options - design case study1 Three potential reflector feed antennas that will be investigated in this case study

Information on these antennas can be compared using the Antenna Magus "compare" option in the information browser. A "side-by-side" view in which information is arranged and displayed as shown below:

Side-by-side compare of three antennas Side-by-side comparison of three antennas' information documents supplied by Antenna Magus. Click on image to enlarge.

Next the engineer adds each of these antennas to the collection, which triggers an automated "Reference Design" using the relevant objective values from the specification. Since not all the required values have been included in the specification, further designs are added to each antenna in order to try and achieve the required -10 dB beamwidth of 80 degrees.

Axial-choke antenna design in Magus - design case study1 Axial-choke conical horn antenna design. Preview taken from Antenna Magus software. Diagonal horn antenna design in Magus - design case study1 Diagonal horn antenna design. Preview taken from Antenna Magus software. Corrugated horn antenna design in Magus - design case study1 Corrugated conical horn antenna design. Preview taken from Antenna Magus software.

Note that in most cases Antenna Magus allows the user to design antennas for different objectives like gain, beamwidth and frequency. The corrugated horn can also be designed for 10 dB beamwidth which was specifically implemented for reflector feed design. The Axial-choke antenna can also be designed for "main beam flatness" which is often a requirement for reflector feed design as a flat main beam with a steep drop-off illuminates the dish uniformly with very little spill over.

Although Antenna Magus has no 10 dB beamwidth design option for the Axial-Choke and Diagonal Horn the quick estimated performance feature offers an alternative solution. Antenna Magus' quick analysis feature (called estimated performance) is ideal for doing a few rough simulations to find out which design comes close to the 10 dB beamwidth specification, seeing that in this case a single simulation takes only a few seconds. />

The following graphs show the estimated performance for all three antennas.

Axial choke gain graph - design case study1 Axial-choke antenna estimated E- and H-plane gain Diagonal horn gain graph - design case study1 Diagonal horn antenna estimated E- and H-plane gain Corrugated horn gain graph - design case study1 Corrugated horn antenna estimated E- and H-plane gain

The numeric estimated performance data can also be exported to compare the results on the same graph as shown on the next image, where the normalized H-plane 10 dB beamwidth of all three antennas is compared. So far it seems like the Axial Choke antenna will be the best option as it has a nice flat main beam with steep drop-off which is ideal for uniform reflector illumination.

Reflector feeds overlayed to see 10dB beamwidth - design case study1 Comparison of 10 dB beamwidth of three antennas' estimated performance

Once the engineer is satisfied with the designs, the final step is to export the "ready-to-run" antenna models to CST Studio Suite® where the antenna elements can be further designed and optimized to meet the given requirements.

The ready-to-run models exported by Antenna Magus at the click of a button would save an engineer several days (if not weeks) that would have been spent building and adjusting simulation models to be ready for accurate analysis and optimization.

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