Consequences of Noise
If there would not be any noise, we would be able to determine the phase difference very accurately for each frequency component. In practice, however, each frequency component consists of a contribution of the desired or undesired signal and a contribution of the noise. This noise causes phase noise. The maximum deviation in the phase difference resulting from the noise increases as the signal gets smaller with respect to the noise.
Therefore, suppression of a weaker interfering signal demands a wider phase window. If an interfering signal is roughly as strong as the noise, the need to suppress it will also be lower. Parallel to this is the fact that a stronger interfering signal needs a smaller window to be suppressed. So this works out the right way.
As the signal-to-noise ratio decreases, the achievable directivity decreases as a result of the necessary wider phase window. This is a disadvantage for weaker desired signals, as you would require of all things, stronger directivity for this. For local (normally weaker) interference, it is possible that one of the antennas picks up the interference at a lower level than the noise level. One receiver then receives frequency components from this interference and the other only noise components. The phase difference is then dominated by these noise components. The result is that the interference components are spread out over 360°. The result is that interference with regard to phase difference is similar to noise.
Last update: September 24, 2006