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From: David Jefferies
Date: 09 Dec 2001
Time: 08:18:38
Remote Name: 195.92.194.14
Charles,
The two outputs from the dipoles are combined in anti-phase, that is, they are subtracted. When they are exactly equal in amplitude and phase there is a null. This happens at broadside to the array whatever the spacing.
Your case is different; the signals are added, not subtracted, and the lambda/2 phase difference is provided by the time of flight from one dipole to the other. That case therefore gives a null along the boom joining the antennas. That is why they specify that the spacing has to be less than a half-wavelength... there will be no extra nulls.
regards
David.