CST Studio Suite: Domain Decomposition solver vs. Time Domain Solver

When designing and simulating periodical structures, like arrays, engineer wants to have reliable tool, that doesn’t require hours of setting up. Simulation time plays significant role here as well – when working with arrays we have structures much bigger that wavelength with millions of mesh cells.

Recently I have been actively using Domain Decomposition Solver (DDM) in CST Studio Suite. In this short article I would like to share my opinion on it, provide comparison with Time Domain Solver and draw some general conclusions about the new solver.

What is Domain Decomposition Solver?

DDM is essentially Frequency Domain Solver, that we have been using in CST for a long time. The difference is in meshing, as it fractions the structure into smaller blocks – domains – and adapts meshing for each domain.

Fig. 1 Cavity array with domains view.

On figure 1 you can see 2 colors of domains: orange color means base blocks, that fill evenly boundary box; pink color means element blocks, that contain an array element inside and have first priority.

Why need for an alternative solver?

Modern mm-wave applications often require big number of antenna elements in arrays. For example, some RADAR arrays consist of hundreds of elements, which makes simulation model heavy for simulation.

Figure 2. Dual-polarized cavity antenna array.

Let’s look at simple cavity mm-wave antenna array, that works at 24-32GHz range. It is 4x4 array, that gives us 16 elements in total, or 16 ports. Most of mm-wave application require dual-polarization, which multiplies number of ports by 2, resulting in 32.

Time Domain Solver calculates each port sequentially. It means that the more ports you have, the longer simulation time you get. When count goes on hundreds, it can result in days of simulation.

On the contrary, simulation time with Frequency Domain Solver is independent from number of ports in the structure. It comes with a price, of course. Direct Frequency Solver require big amount of RAM for managing big simulation, and sometimes you just do not have enough to work with.

By dividing structure into smaller domains DDM solver gives a good simulation speedup, as domains can be solved in parallel, depending on the number of cores. If your structure contains geometrically identical elements – like antenna arrays – DDM solver allows setting up of repetitions.

Good news – with DDM solver the peak memory relates to the number and size of domains per core. By making the domains smaller the peak memory can also be lowered.

Let’s compare

Hardware in use: 2x18 cores, 128Gb RAM

Fig. 3 Radiation efficiency comparison

Fig. 4 Radiation pattern comparison

In conclusion

Here are some pros and cons that I have noticed while working with Domain Decomposition Solver:

As always, each time engineer should decide which tool to use in order to achieve better results. Every option comes with a tradeoff. In my opinion, DDM solver is a good way of simulating periodic structure, which allows to use full potential of the solver.