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Re: antenna gain



At 07:27 PM 12/19/99 +1300, Robin Francis wrote:
>advise me the effect of giving two in phase antennas eg stacked yagis 
>unequal drive power. Would it cause beam deflection in the same way as a 
>delay line in the feed to one antenna.

Feeding signals of unequal power but same phase to the two Yagis will 
reduce the gain of the array, but the peak of the antenna pattern will be 
in the same direction as it would have been if the antennas had been fed 
with equal power.

Here's a simple nonmathematical thought experiment to help see this.  Walk 
around the array, in a circle, a fixed distance from the array.  Where will 
the signal you receive be maximum?  Must be where the radiation from the 
two antennas arrives at your location with the same phase.  Because the two 
(identical) antennas are driven in phase, radiation from the two antennas 
will be in phase when the distance between you and each of the antennas is 
equal.  This argument doesn't involve the amplitudes of the signals fed to 
the two antennas, so works for all amplitudes.

A common cause of unequal power in an array is mismatch.  Unfortunately 
mismatch can affect both signal level and phase.

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