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Re: Inverse Square 'law' Re: About wireless energy transfer



Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 07:12 PM 2/9/2007, you wrote:
Original poster: "Gav D" <gdingley@xxxxxxxxx>

Hi,
I think it is still an inverse square law, because although you are
focusing the power, it's density is still falling off with the square
of distance, as a perfect beam is impossible. The reflector (or
whatever focusing you are using) only increases the gain of the
radiating structure.

That said, I did try to record the inverse square law with a couple of
10GHz horn antennas, but the power appeared to roll-off at a rate of
1/r. Horn antennas have a gain of only 1.5 I think. I think my
numerical processing is to blame, 1/r^2 should hold.

How far were you from the horn. You have to be in the "far field" for the 1/r^2 to hold. Most horns have a gain substantially higher than 1.5.. more like 10,15, or 20 dB. A 20 dB horn at X-band is going to be about a foot across.