Dear Pudu,

The reason is very simple. Both the solvers solve maxwell equations on the geometry under simulation. The designer has to see which analysis ( time or frequency) is less memory consuming. Generally time domain calculations are more memory exhaustive. The scenario is very similar solving a equation in time and solving it using a fourier transform, which converts a differential equation to a algebraic equation.

@Anuraag Misra

Dear sir,

wil it give same results when the design is simulating with both the solvers.

Dear Pudu,

If u model correctly it should give practically similar answers.

Both Solvers should give you the same results. For instace, a patch antenna is simulated using CST and HFSS should give the same results in terms of matching, radiating pattern and etc ...

Thank u all

All the EM solvers are based on solving Maxwell's equations in different forms. simply Time domain solver is base on solution  of differential form form of Maxwells  equations. The most powerful tool of CST is its time domain solver. Generally time domain solver takes less memory as compared to frequency domain and is faster. But it is important to note that the speed and memory requirement for computation may vary from structure to structure and their complexity. In some some cases frequency domain solver  takes less time than other depending upon transient behavior of the source of excitation and modes. For frequency domain  solving the best choice is to use HFSS. Both the solvers give nearly same result .

In CST, time solver uses FIT technique and it is good for wide band-widths. well its mesh is rectangular like FDTD or other time domain techniques. for curved shape structures you need to increase mesh number or decrease mesh size to get a good result, and that results in more resources like memory and time.

on the other hand, frequency solver, the solution is valid in single frequency; I mean the mesh is made based on the criteria of convergence in single frequency and if you do sweep frequency, the results are valid as long as the mesh size would be valid in those frequency bands, no large frequency sweep is advised.

The time domain solver is good for wide band structures and the frequency domain is good for curvy structures; in their intersection, wide band and curvy structures like Spirals, there is a tradeoffs between these 2 solvers whether it is good to solve the problem in time domain with large meshes or to solve the problem with frequency solver with different frequencies and sweeps.

As Biswajit Dwivedy Mentioned, HFSS is better than CST in Frequency domain. I experienced the difficulty of Spiral antenna in CST Time domain, and I thought I rather use HFSS FEM Solver; and I found it better and quicker than CST Time domain EVEN with different frequency solutions and sweeps !

I simulated patch antenna in CST and HFSS,but the results are not same

Both time domain and frequency domain solver divides the structures into tiny blocks.

In time domain, the mesh is created in X, Y and Z axis and tiny blocks look like cubes. Harmonic Equations in differential (or integral) form can be used to analyse those blocks.

In frequency domain, FEM (finite element method) is used to break the surface into small triangular objects and integral equations are used in phasor form for those tiny surfaces.

NOTE: While time domain in CST is relatively fast, the waveguide-ports has to be aligned (be parallel to) either X, Y or Z axis. In frequency domain, the waveguide-port can have arbitrary directions.

To Md Talal

CST time domain and HFSS have different answers. This can be brought close to each other by improving the mesh in CST and improving the boundary conditions in HFSS. In CST you can try adaptive meshing, to get better results.

Any experience about FEM using Comsol solver? Any comments or suggestions

Both solvers give nearly the same result.

help

iam using the CST 2017 and when using the tie domain solver it show me an error "Time Domain Solver (HEX) terminated abnormally."

knowing that i uninstall and install it more then 10 times

Thanks for your contributions

Dear Biswat Diwedy i want why simulation time takes larger in some antenna and smaller in other. Is there any specific reason.

Time Domain Solver (HEX) terminated abnormally ! I met this error

many times,who could tell me how to solve the error

Dear Zeeshan Ahmed Lodro, The fact of time consumption may be analyzed in a simple method. Example. for time domain solvers:

For a larger /wide band structure the corresponding time domain signal becomes very small. As the time time domain equations mostly involve time derivative terms which becomes easy for the signal of lower duration. Similarly lower frequency structures take relatively more time. In most of the cases this factor mainly affect the computation and time.

thanks for all ... iam now using cst 2018

can u share download link for CST 2018 or 2017

For the big structure, Time domain solver is the appropriate solver

Time domain solver uses FDTD method to solve the maxwell's equations. Frequency domain solvers uses FEM (finite element method) to solve the maxwell's equation. The two solvers uses two different methods to solve the same problem. Both solvers are originally from the FIT - Finite Integration Technique - which works on the Integral Formulation of the Maxwell Equations. Thus, it is pertinent that both solvers give same (Approximately) results. If the model is correct and simulation parameters are properly defined for both solvers they do give similar results (not exactly same). Time domain is the strong tool of CST and can be very useful to simulate large structures (Less memory). Frequency domain solvers are useful for smaller structures like unit cells and FSS. Floquet analysis can be done using frequency domain solver.

Dear Colleague,

hope this will help

https://www.researchgate.net/post/What-is-the-reason-for-getting-different-results-in-time-domain-solver-and-frequency-domain-solver-in-CST

Most of the times, the difference in results happens because of an unsuitable mesh configuration which is defined in time domain solver. The TD solver is highly sensitive to the mesh concept. In the FD solver the mesh type and size are usually defined automatically and accurately by CST which leads to higher accuracy. But, as far as I am concerned, it usually fails when defining suitable mesh configuration for Time Domain solver. Personally, I suggest you increase your mesh number in TD solver. Moreover, changing the mesh type to FPBA may also improve your TD results. With this configurations, in most cases, the difference between the two solver will be reduced. Other mesh settings will also be helpful if are utilized consciously.

However, there might be some specific instances that other factors may play a role in the accuracy such as the particular forms or singularities of the structure.