EM wave polarization from radiating antenna
The polarization of a EM wave is define by E field of plane wave. Plane wave occurs in the far-field of a radiating antenna.
Am i right to say that even in the radiating near-field, the polarization of the EM wave is already defined ?
yes. Basically polarization is defined w.r.t. earth GND.
I'm referring to polarization as in Linear, Circular & Elliptical.
For an antenna in general, there are 1/r, 1/r^2 and 1/r^3 terms for the field.
In the near field, the 1/r^2 and 1/r terms are non-zero.
Can i say that since the 1/r term exist also in the near field, the polarization would be independent of distance.
You got the point,
but do not consider the magnitude term alone but also the phase or angle which is important at near field.
This subject is important in RADAR where you want to place both RX and TX and operating CW.
let say it is point source, and if you are using the linear polarization, then the angle of source and observation is not in parallel in case of near field. Let assume that source and observation are at different heights hence you will find the cos( angle) factor. this position the polarization angle is tilted by the same.
I mean if vertical polarization is used at the source then exact vertical polarization can not give the maximum power at the observation point if the observation polarization also vertical. the observation polarization will shift by the angle of separation between the source and observation.
The other point is at near filed it is more summation of the source and reflections and resulting a pattern.
Hope this helps you.
you can not say as the distance is creating the change in angle for near and far filed.
So,
In the NF, if the Tx and Rx are not aligned properly, a CP wave would become an Elliptical wave.
Thanks, I'll read up more about radar.