An antenna array is a system of multiple connected antennas, or radiating elements, which work together. Antenna arrays are designed to achieve radiation maxima, using constructive interference, in the direction which is intended to be used for transmitting or receiving electromagnetic energy. By utilizing antenna arrays, it’s possible to achieve radiation performance characteristics which are not achievable by a single antenna element. Unfortunately antenna arrays are typically more complex and costly to design and manufacture compared to single antenna elements. However, utilizing the Array Task in CST Studio Suite, it’s possible to streamline the design process. This blog post will guide you through the Array Task simulation workflow in CST Studio Suite.
Figure 1. Shared Aperture Array
Assuming that all antenna elements within the array are identical, the radiation performance characteristics of the array can be divided into two main parts;
The Array Factor depend on the following;
Once you have simulated an antenna in CST, you have the possibility to estimate the performance of an array by applying an array factor. This estimate is a bit rough since it doesn’t account for the mutual coupling between the antenna elements, and the edge effects of the array are not considered. It does however provide quick and valuable information for dimensioning the antenna array.
Figure 2. Array Performance Estimate
The next step of the simulation workflow would be to setup an Array Task. The array task comes with a few pre-defined shapes as can be seen in the figure below, but you also have the possibility to define the array configuration using a .tsv file where the 3D position of each radiating element can be set individually. In this example we’ll show a simple patch antenna array, but it’s also possible to setup e.g. shared aperture antenna arrays including radome and enclosure as shown in figure 1.
Figure 3. Array Layout Configuration
Once the array configuration is setup you have 2 options for array simulations;
Figure 4. Array Simulation Projects; Unit Cell (left), Full Array (right)
The Unit Cell simulation project simulates an infinite array. For large arrays there are many more center elements than there are edge elements, i.e. most elements in the array behave like, and can be represented by a Unit Cell. By using this approach you can optimize your array performance while accounting for the mutual coupling between the antenna elements. For large arrays it’s typically much faster to run a unit cell simulation than a full array simulation, and because of this it’s suggested to optimize the element design using the unit cell approach.
The full array simulation is the most accurate as it also accounts for edge effects of the array, therefore it’s recommended to run a full array simulation to verify the design before manufacturing real-world prototypes. It’s of course possible to further optimize design using the full array simulation, but as mentioned before, the simulation time might be extensive. Luckily, there are acceleration possibilities to speed up these calculations. If you’re using the time domain solvers, you can make use of GPU computing. While if you are using the Frequency Domain solver, you can use the Domain Decomposition Method (DDM Solver) which is well suited for large periodic models. It’s able to efficiently find and group repeating geometries in the array to speed up the simulation.
Full array: excitation settings
When setting up the full array simulations, there are a few options to chose from when it comes to exciting the array;
Figure 5. Antenna Array with Elements Arranged in Groups
As mentioned before, it’s possible to define different array excitations in the Array Task. It’s possible to easily apply common amplitude tapering schemes, such as uniform, cosine, Taylor, etc, as well as then applying different phase shifts or scan angles directly within CST. However, it also It’s possible to load .tsv files to CST where both amplitude and phase values are specified for each element.
Figure 6. Antenna Array with Taylor Amplitude Tapering
The array task also support subarrays, i.e. that each element of the array actually is an array. This is supported for both the unit cell and the full array simulation projects.
By utilizing the array task in CST Studio Suite, array design and optimization is made more efficient than a traditional, manual, workflow. The array task is available for all CST users, and it helps automate the complete workflow; all the way from modelling, simulation setup and result analysis using powerful postprocessing features. Simulation throughput is an important factor for many design teams and by working smarter, you’ll be able to get your results faster. CST Studio Suite supports both time domain and frequency domain solvers allowing you to select a solver suitable for your compute resources. It also allows you to build extra confidence in your design, as this allows for cross-verification of results - you can easily change the numerical method without having to re-model your simulation project.