Computer Simulation Technology (CST) Microwave Studio and High-Frequency Structure Simulator (HFSS) are the two most common design tools for RF simulation. Most Taoglas antenna simulation models are available in CST to enable customers to build simulations models using Taoglas antennas inside their custom design environment.
This means device OEMs, systems integrators and others now have access to the same models that Taoglas uses for its internal simulations, with only the proprietary information hidden. These models are a convenient way to get a good sense of how a particular antenna will perform when integrated with your devices.
Follow these nine easy steps to start using Taoglas CST models. If you do not own a copy of CST software, it’s still possible to achieve an early understanding of how Taoglas antennas would work on your PCB by using the Antenna Integrator Tool at https://www.taoglas.com/taoglas-antenna-integrator.
Select an Antenna and Download Its Model
Taoglas has one of the most extensive catalogs of antennas for cellular, GNSS, NFC, UWB, Wi-Fi, and other technologies. Start by searching antennas at https://www.taoglas.com/product-category/embedded-antennas. Although a CST file is not available for every antenna, the most popular ones have it.
Here’s an example using the Taoglas WLA.01. Simply click on the link to download the encrypted CST file.
Open the Model File in the CST Tool
Open the file in CST Microwave Studio. (Taoglas recommends using the latest version and service pack of CST when conducting simulations.) You may see a popup when opening the file to say it was created in an earlier version of the program. If so, click okay to convert it to the version of CST that you are running.
When the file opens, you will see an encrypted version of the WLA.01 on an evaluation board. This encrypted version has an orange mesh placeholder to protect the antenna’s IP while allowing the antenna to be authentically simulated.
Simulate Antenna to Verify that the File is Working
Before starting to integrate the antenna into any other designs, Taoglas recommends simulating the encrypted file with no changes. This shows the simulated antenna performance you could expect. Taoglas recommends using the time domain solver.
Although Taoglas tries to ensure all available CST models match our datasheets, you may encounter some inconsistencies, mainly in the simulated eff vs datasheet efficiency. This is due to the sometimes complex antenna designs that have to be simulated. Taoglas aims to provide models where the first priority is that the antenna is tuned to its correct band, with the antenna’s efficiency being secondary.
Create or Open Your PCB
Next, create a PCB where the WLA.01 will be integrated. If you already have a PCB created in CST, open that file now. If you have a DXF/Step File of your PCB, that can be imported and used to create your PCB if one does not exist. Or if you use Altium Designer, An ODB++ file can becan be exported from that program and imported into CST.
Otherwise Taoglas recommends creating your PCB using CST’s modelling tools. If PCB height has not been defined, Taoglas recommends using a 0.8 mm thick substrate (FR-4) and a 0.035 mm thick top and bottom ground (copper annealed).
Import WLA.01 CST file into your file. Finally, add vias to connect your top and bottom grounds. You can use the evaluation PCB that comes with the encrypted file as reference because it is unprotected.
Integrate the Antenna onto the PCB
To import the Taoglas WLA.01 into the file with your custom PCB, select the modeling tab and click Import/Export -> Sub-Project. Select the WLA.01 CST file when the explorer window opens.
You have now successfully imported the Taoglas WLA.01 CST file.
There are a number of ways to integrate the Taoglas encrypted model onto your own PCB. If you are unsure where to place the antenna, please refer to the product’s datasheet. For the purpose of this guide, Taoglas recommends the following:
- Create a boolean block, the same size as the keepout in the encrypted file/datasheet and as thick as your PCB.
- Use the boolean to remove any copper layers in the antenna integration area on your PCB.
- Select the components included in the WLA.01 encrypted file (Except the Top and Bottom Ground and the reference PCB) and use the ‘transform tool’ to move/copy them to the antenna keepout area you created on your PCB.
- Remove any further top ground required to recreate the CPW feed of the WLA.01 antenna on your PCB.
Fix Any Potential Issues, Such as inconsistent Copper or PCB Thickness
It is important to ensure that all copper on your PCB is the same thickness. If your PCB or copper thickness is different compared to the reference PCB included in the encrypted file, then the CPW feed would have to be recalculated to ensure it is 50 Ohms. If the CPW feed is not 50 Ohms performance would be negatively affected.
Add Lumped Elements
Once your CPW Feed is correctly setup, the next step is to add any required Lumped Elements.
One option is to use the lumped elements included in the WLA.01 CST file. These are also the datasheet values.
Note: You may have to vary the lumped element values from the datasheet if your PCB changes detune the antenna. Detuning may also occur if you simulate more of your device, like an enclosure.
To add your own lumped element, two points or edges must be selected using the Pick Points tool. Pick the center edge of the end of your antenna feed and the center edge of the ground on the other side of the keep-out area.
This opens a window where you can define a lumped element between your two picked points.
For example, to create an inductor(L), add a value inside the box denoted with L and leave the rest of the boxes at 0. A similar process can be followed to create a capacitor(C) or a resistor(R).
Define a Port
Finally, before simulating your creation, a port must be added. CST allows for both discrete and waveguide reports to be created. For the purpose of this guide, and for the majority of Taoglas encrypted CST files, a discrete port is used because it is a simpler process.
To add your port, two points or edges must be selected using the Pick Points tool. Pick the center edge of the end of your antenna feed and the center edge of the ground on the other side of the keep-out area.
Once selected, navigate to the simulation tab and select discrete port. Then click OK on the window that pops up. Your discrete port has now been created.
Set Up a Simulation
Once the lumped elements and port have been created, the PCB can be simulated. One tip is to go to the Mesh view and ensure that the PCB has a mesh whose resolution is high enough to accurately simulate your model. Please refer to CST’s documentation for more information on Meshing.
Additionally, in order to see antenna efficiency or the farfield gain, field monitors must be added. To add these, navigate to the simulation tab and select Field Monitor.
Field monitors have many uses, but for the purposes of graphing the antenna efficiency, select Farfield monitor when the dialog box pops up.
Once selected, you can pick the frequency you wish to monitor. Click apply and add the remaining frequencies.
Once you have added your list of monitors, you are ready to proceed with your simulation by clicking Start Simulation.
Once complete, your results will appear below in 1D Results.
