Question about equivalent sources in Feko

Altair Forum User

Dear,

I'm having an exercise which I want to illuminate a sphere by a plane wave and export the near field at the surface of the sphere. Then I want to import that near field in a separate model as a spherical aperture field to radiate to a horn antenna to receive the voltage. Right now I don't know if my approach is correct since Feko cannot import the current distribution on the sphere as the source. So I want to ask if the near field at the surface of the sphere is equivalent to the scattered field radiated from the sphere after being illuminated by the plane wave. I would appreciate if anyone can show me how to test it too.

Thanks,

Tuan.

Johan_Huysamen

Dear Tuan Nguyen

 

The near fields sampled at the surface of the sphere would include both the fields scattered by the sphere and the incident fields from the plane wave.

 

If you are interested in only the fields scattered by the sphere you should modify your near field request by selecting the 'Calculate only the scattered part of the field' option under the 'Advanced' tab.

 

If you then use these fields as the aperture source in another model, this would represent only the fields radiated by the current on the sphere.

 

Regards,

Johan

Altair Forum User

Dear Johan,

Thank you for your response. I want to validate that concept by testing the Radar Cross Section by creating a spherical aperture field from the sphere of the first model then I request the far field of another object being illuminated by that aperture field. However the far field result cannot show the Radar Cross Section like when I request it with the plane wave and the sphere in the first model. Do you know why or maybe I misunderstand the concept ?

Thank you,

Tuan. 

JIF

Dear Tuan Nguyen

 

You are correct, for RCS you need a plane wave. See the equations in user manual (20.6 Far fields and receiving antenna) and note that these assume a plane wave excitation.

 

It sounds like what you are trying to calculate is the reflection from an object due to some source, other than the original plane wave. If the object(s) is far from the source, you should be able to approximate the source as a plane wave instead of using the actual source (if they are well separated, only the field in the direction of the object will be seen by the object). If they are not, I'm not sure that RCS (a far field concept) is the correct way to investigate the reflection effects that you are interested in.

 

Without understanding more about what you are trying to do or investigate, it is quite difficult for me to make suggestion for your simulation.

 

Regards

JIF