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Technology Stocks : KVH Industries, Inc.
KVHI 5.990+4.1%Nov 4 3:59 PM EST
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To: robert b furman who wrote (1556)11/29/2002 5:52:55 PM
From: Michael Dunn  Read Replies (2) of 7249
 
Bob,

I was trying to follow where the 49 came from but couldn't...?

Phaseshifting, in both transmitting and receiving systems, is different than what you have described.

The simplest description I can think of is to draw an analogy to a regular dish antennae. The amount of signal collected is proportional to dish area, the dish focuses the signal on the reciever (located at the dishes radius). As the dish is moved away from pointing at the satellite a few things happen:

1. The signal reflected off the dish starts to miss the receiver

2. The dish's effective collecting area drops by the cosine of the angle you've tipped it away.

and

3. Different portions of the disk are different distance from the satellite. If these different distances are on the order of the transmitted wavelength the signal arrives at different section of the disk with a different phase and rather than constructively interfering at the receiver (to give a strong signal) they destructively interfer (partially canceling each other out).

A phased array antennae, by compensating phase across the array, avoids problems 1 and 3. When signal hits the array off normal the array electronically compensates the signal received in each element of the array so that when the signal from every element is added up they are all in phase and as a result give a strong signal. So, a phased array is steered electronically so that, as it or the transmitter is moved, it electronically points at the transmitter and the only impact is a drop in collecting area with the cosine of the angle between the signal and the array normal.

A phase array that transmits works the same way, by adding phase shifts to different array elements you change the location on the ground where the signal from all the elements arrives in phase. This steers the beam.

Mike
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