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# Distance to source for impinging waves planar

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#### Circuit_seller

##### Full Member level 5
Planar Wave

Hi

What shuould be distance(in landa) of a source to an receiver antenna, to become impinging waves planar?

Re: Planar Wave

hello,

isn't this the same as the far field condition used in e.g. antenna measurements?

best regards

Re: Planar Wave

for far field condition:

L ≈ 2D²/λ

L is the measure distance , D is the antenna dimension

λ is the wavelength .

Re: Planar Wave

Hi

Length of antenna(monopole) is 1 meter and wavelength is 2 meter, so according to your formula L is less than 1 meter.
I think it is wrong.

Re: Planar Wave

this depends on the size of receiver.

Re: Planar Wave

Hi

What do you mean by size of receiver?

Re: Planar Wave

the formula could be found in electromagnetic book ,

I think it mentions that if L is large enough , and it could be

identified a far field.

L >> 2D²/λ

Re: Planar Wave

Well, you can not achieve a real plane wave. But you can create an approximation to it. What you need is an electromagnetic wave whoose amplitude and phase does not vary over a certain area. So the distance required to obtain such an approximation does depend on the size of the antenna or the aperture of the antenna.

Re: Planar Wave

Thanks irfan1

Suppose i have a 1m monopole antenna on top of a car, transmitter frequency is 140MHz and the eviroment is reflection free, what should be the distance from transmitter to receiver?