Learning Forum

[ivanivanch47]

I need to conduct a simulation of an antenna in HFSS (for example, a horn). The HFSS Help has instructions on the minimum distance from the antenna in lambda/3 at the solution frequency. However, if it is necessary to evaluate the antenna characteristics in the frequency band, there are different opinions in open sources.:

1. Set the default settings. Calculation of the offset of the radiation boundary relative to the frequency of the solution (for example, relative to the central frequency).

2. Calculate the offset of the radiation boundary relative to the lower frequency in the spectrum, and set the upper frequency in the solution settings. 

3. Creation of several solutions for different frequencies with different sizes of the radiation boundary.

 

Please tell me the correct approach to calculating using Radiation Boundaries. Thanks!

[Takeshi Itadani]

If the frequency range you want to examine is wide, method 2 is the most accurate.
However, if, for example, radiation is strong at a specific frequency, you can set that specific frequency as the analysis frequency, create an analysis space at a distance of λ/3 from that frequency, and then set the radiation boundary conditions.
It is recommended to perform both analyses and adopt the one that yields results closer to your expectations.

Also, consider using FE-BI instead of Radiation boundary conditions. With FE-BI, even in analysis spaces where the antenna is separated by a distance of about λ/10 to λ/20, it functions sufficiently as an absorption boundary condition.

[ivanivanch47]

Thank you for the detailed reply. Do I understand correctly that if I do not use a hybrid solver (with geometry containing IE regions, for example, if I supplement the model with a reflector), then the boundary conditions of PML and FE-BI as an absorber will not differ for this case?

[Takeshi Itadani]

PML boundary conditions place a virtual object at the boundary surface that causes high loss at the frequency specified during the setting process. Therefore, its accuracy as an absorption boundary condition may be poor at frequencies other than the specified frequency.

 

FE-BI, on the other hand, analyzes the boundary surface of the analysis space using the MoM method during adaptive analysis, making it the most accurate absorption boundary condition.

 

We recommend using FE-BI as an absorption boundary condition. However, FE-BI cannot be used when multiple materials are in contact at the boundary surface or when used in conjunction with symmetry boundary conditions; in such cases, use radiation boundary conditions.

 

Furthermore, FE-BI cannot be used in conjunction with Lattice Pair boundary conditions; in such cases, use PML boundary conditions.