What is the default distance (in terms of wavelengths) at which the far fields are calculated in Feko?

Vishakha Pandharpure_20595
Vishakha Pandharpure_20595 Altair Community Member
edited June 20 in Community Q&A

Hi

I have been simulating an antenna in Feko (MoM & FEM) & CST (FDTD) . The peak gain variation w.r.t. frequency has been different for the antenna in Feko & CST. In CST-FDTD there is a setting by which the distance between the antenna structure & the PML ( perfectly matched layer) can be changed. The default value for this parameter is wavelength/4. ( wavelength can be centre, monitor or user defined).  Also, the estimated reflection level is adjustable. The default value is 1e-04. At the default values the CST peak gain w.r.t. freq. differs from that in Feko. But when

a) the distance between the antenna structure & the PML is reduced or

b) the estimated estimated reflection level is reduced or

c)  distance between the antenna structure & the PML is increased AND the estimated estimated reflection level is reduced     

the peak gain behavior in CST matches reasonably well with Feko.

I am trying to understand this phenomenon. Is there a similar mechanism in Feko far fields calculation which employs a PML at a certain distance from the antenna structure? If yes, what is that distance and what is the estimated reflection level?  

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Answers

  • Zeina
    Zeina
    Altair Employee
    edited June 19

    Hi Vishakha,

    In Feko you can access the boundary condition settings for the FDTD solver by going to Solve/Run > FDTD Boundary. You then have access to multiple parameters:

    image

    Please check the related help section where you can find more details about each parameter.

    Best Regards,

    Zeina

  • Vishakha Pandharpure_20595
    Vishakha Pandharpure_20595 Altair Community Member
    edited June 19

    Hi Zeina 

    Thanks for your reply. 

    I am using MoM and FEM in Feko and FDTD in CST. Is there any similar setting in the MoM or FEM solving methods in Feko?

     

    regards

    Vishakha  

  • Zeina
    Zeina
    Altair Employee
    edited June 19
    Vishakha Pandharpure_20595 said:

    Hi Zeina 

    Thanks for your reply. 

    I am using MoM and FEM in Feko and FDTD in CST. Is there any similar setting in the MoM or FEM solving methods in Feko?

     

    regards

    Vishakha  

    Hi Vishakha,

    It is first important to understand what PML is and when it is used. PML is a boundary condition used for problems with open boundaries , most commonly with finite difference and finite element methods.

    In FEKO, if you are using MoM or the coupled FEM/MoM, PML is not applicable and other types of boundary conditions are applied. So for these cases, your questions are not valid since there is no open boundary being applied as such.

    If you wish to decouple FEM from MoM (Solver Settings > FEM tab > Decouple from MoM), and to solve the open model fully using FEM, you have to manually create the absorbing boundary around the model in the form of an airbox. You can then change the dimensions of the box and see its effect on the results.

    Best Regards,

    Zeina

     

     

  • Torben Voigt
    Torben Voigt
    Altair Employee
    edited June 20

    Hi Vishakha,

    In contrast to FDTD, it is not necessary to have such a boundary for MoM and FEM (actually hybrid FEM/MoM). MoM can calculate the field anywhere in space using Green's functions. The far field in Feko is calculated at (theoretically) infinite distance.

    Best regards,
    Torben

  • Vishakha Pandharpure_20595
    Vishakha Pandharpure_20595 Altair Community Member
    edited June 20

    Hi Torben Voigt

    Thanks a lot for your message. It is definitely helpful. 

    Regards

    Vishakha

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