antenna-theory.com

[Sinlkid]

Hi,
I have some problems to understand how to calculate the far field when a scattering object stands between a transmission und receiving antenna (Tx-Obj-Rx are in line). In my case the object is a windturbine with lets say a hight of D=100m. The frequency of my transmission system is f=90MHz (lampda=3.33m).

I know how to calculate the far field distance from the transmitter to my object (2D^2/lampda), but i don't understand how to calculate it from the object to the receiver.

Do I need to calculate it the same way, as if the object wasn't there, so I use the size of the receiving antenna instead of the dimension of my object?

Why do I need this? I have to know if the reciever is in the near or far field of my wind turbine not of the transmitter.

I hope you can help me.

Thank you.

[R. Fry]

Depending on how accurately you construct the physical model of this situation, NEC (Numerical Electromagnetics Code) can produce good insight toward answering your questions.

In general, VHF/UHF signals tend to diffract around many narrow-profile physical structures with little practical effect on the far fields beyond those structures.

Consider the cases of the VHF/UHF broadcast antenna systems mounted on vertical pylons installed on a "candelabra" support structure, such as at Mt Sutro, CA (http://en.wikipedia.org/wiki/Sutro_Tower).