Electromagnetic simulation is more challenging for antenna design as size, frequency, and materials increase. Several solutions are provided by Altair Feko such as Method of Moments (MoM), Multilevel Fast Multipole Method (MLFMM), Finite Element Method (FEM), and high frequency techniques. Solver choice varies depending on the electromagnetic problem, electrical size, materials, required accuracy, and available computer power.
Start with Electromagnetic Problem
Solver choice should be made starting from understanding of the problem rather than making a particular technique choice. The frequency of operation is one of the considerations since wavelength is getting smaller as frequency increases. Thus, the same physical structure can have different electrical sizes depending on frequency.
Electrical size affects number of unknowns, electromagnetic coupling, memory, and simulation time. So, engineers should evaluate electrical size of their structures taking into account the wavelength.
MoM for Full-Wave Analysis
The Method of Moments (MoM) is a full-wave technique that is often used to analyze antennas and conducting structures. This method can solve for unknown currents and provide information about radiation, current distribution, and electromagnetic interaction.
A single antenna or small conducting structure may be appropriate for use with the MoM when it requires detailed full-wave analysis. But as the model increases in electrical size, it becomes computationally more challenging.
This aspect becomes especially important in the case of moving from one antenna to a larger array because electromagnetic interactions become many times more than with the single one.
MLFMM for Large Full-Wave Problems
The MLFMM is supposed to improve the efficiency of full-wave analysis for electrically large problems. By organizing the electromagnetic interactions, MLFMM reduces the computational effort necessary for large models.
For instance, the single broadband Vivaldi antenna is manageable in terms of computations in the traditional full-wave environment. If we increase the model to the 32-element array, then the problem becomes much harder.
In this situation, MLFMM should be considered when detailed full-wave analysis is needed for the electrically large problem. Thus, the decision depends on both model size and the need to retain full-wave electromagnetic analysis.
FEM for Complex Material Structures
Finite Element Method (FEM) is based on the volumetric technique which involves splitting regions of interest into small elements and computing electromagnetic fields in these elements. As a result, FEM is used if the volume behavior of dielectric/material regions is significant for the problem being simulated.
Many conducting antenna problems can be addressed using MoM or MLFMM. But when the detailed behavior of complex volumetric materials has to be modeled, FEM can be used.
It depends on the part of the electromagnetic behavior that has to be captured.
High-Frequency Methods for Large Structures
As a structure starts to span many wavelengths, full-wave analysis might start to require heavy computation resources. High-frequency techniques will offer an alternative approach as long as the assumptions used fit the problem at hand.
Feko offers high-frequency techniques such as Physical Optics (PO) and Ray Launching Geometrical Optics (RL-GO). These are techniques that employ approximations to make computations of electrically large structures less resource-demanding.
For instance, the analysis of a large conducting surface using a full wave technique can be challenging. A suitable high-frequency technique will have to be used as long as the complete analysis of the entire structure is not needed.
But speed of computation cannot be the sole deciding factor in choosing an appropriate approach. The chosen approach has to suit the physics of the problem.
Solver Selection as a Design Evolves
The solver choice may vary as a design evolves. Take a broadband Vivaldi antenna. The antenna itself may need to undergo full-wave modeling at the beginning. When it evolves into a large array, the emphasis starts shifting towards computational efficiency. After the array is mounted on an electrically large airborne vehicle, things get really complicated.
In this case, full-wave modeling would be needed for the antenna, while high-frequency techniques could be used for certain portions of the surrounding structure.
This example clearly demonstrates that the solver choice is not always a one-time decision.
Key Questions for Solver Selection
Engineers must ask themselves the following before picking a solver:
- What is the frequency and the wavelength of operation?
- How big is the structure compared to the wavelength?
- Does it require a full wave analysis?
- Are there complex materials in the problem domain?
- How many elements and electromagnetic interactions are there?
- Is the model electrically large?
- How much computational power do you have?
- Would a high-frequency approximation suffice?
Conclusion
Selection of a proper solver in Altair Feko involves considering the balance between electromagnetic needs and computation efficiency. While MoM can be used for many electromagnetic full-wave antenna and conducting structure problems, MLFMM can be used for larger full-wave problems. FEM can be used when there are considerations of volume material properties, while PO and RL-GO can solve suitable electrically large problems.
It is not the objective to select the fastest or the most advanced solver but one that satisfies all electromagnetic physics, electrical size, accuracy, and computation efficiency of the problem.
Frequently Asked Questions
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