Results of near filed and farfield are not the same!!!!!!

Haj Hassan
Haj Hassan Altair Community Member
edited October 2020 in Community Q&A

Hi,

i have a problem in my simulation results.

What i am not understanding is why the near field and the far field results are not the same?!?!?!?!?

Thanks in advance

 

Best Regards

Haj Hassan

 

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Answers

  • Johan_Huysamen
    Johan_Huysamen
    Altair Employee
    edited May 2020

    Dear Haj Hassan

    From your question I understand that you expect the near field and far field results to show the same type of behavior.

     

    In your model you request the near field values up to Z = 200mm. Given the size of your antenna (including the lens geometry), your near field request only covers the 'near field' region surrounding the antenna. In the 'reactive near field' close to the antenna you would not see radiating behavior in the fields and in the 'radiating near field (or Fresnel) region' the fields would show radiating behavior, but the behavior would still vary based on the distance from the antenna. Only once you sample fields in the 'far field' would the behavior show stable far field radiation.

     

    You would have to sample the fields at much higher Z values to see the 'radiating far field' region that should then show similar behavior to the far field results.

     

    You could use a calculator such as the one below to determine the required distances. Remember to include the lens as part of your antenna when determining the antenna size dimension. 

    https://www.everythingrf.com/rf-calculators/antenna-near-field-distance-calculator

     

    In the extreme case, if you were to request near fields with a spherical coordinate system at a radius of say 10m, you should see the same shape as for your far field request.

     

    Kind regards,

    Johan H

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