near field and far field

[saif haider]

every one from field of electromagnetics knows that their exist to FIELDS

near field... and 2 far field

but when comes to our result we always consider far field and pattern is always used why
why not near field I CAME TO KNOW THAT NEAR FIELD IS SOME WHAT COMPLEX i mean to say that it comtains some complex quantities what r those and why pattern is not consider in that field

 

[snkhan]

Hi
An Em waves consists of electric and magnetic fields propagating through space, a field being a region where electric or magnetic forces act. The electric and magnetic fields in a free space wave traveling outward at a large distance from an antenna convey energy called radiation.

Where field pattern where r is proportional to the field intensity at a certain distance from the antenna in the direction θ and Φ. [Antenna by Kraus] . Moreover at distances that are large compared tot he size of thea antenna and large compared to the wavelenght, the shape of the field pattern is independent of distance.

Regards

 

[mfarhan1]

well actually there are three regions, in first region there is no radiative power only stored(reactive) energy in second region there are both and radiative power starts dominating reactive power, and in far field (fraunhofer region) there is only radiative power, at source the wave is not pure plane wave but as we go further they spread and recieving anteena is in small region as compared to full span of wave so we assume it to be planar, that happens in far field, last but not least if you remember the solution of helmholts equation is based on plane wave assumption and plane wave is in far field only thats why we always consider far field. (oops quite leangthy explanation)