what is Null in antenna?

[simoun]

what is the concept of null in antenna?where the pattern is zero it means we have null?
where mull would be used?
how can i find it?

 

[manvindar]

it is angle where radiation fails to zero.......u need a test bench to determine radiation intensity at various angles

 

[simoun]

it is angle where radiation fails to zero.......u need a test bench to determine radiation intensity at various angles

The increasing pollution of electromagnetic environment has prompted the study of array pattern nulling techniques.
These techniques are very important in radar, sonar and communication systems for minimizing degradation in signal to
noise ratio performance due to undesired interference.
what is the nulling techniques? and how does effect on SNR?

 

[jiripolivka]

All antennas have their patterns with maxima and minima. The minima are called "nulls" and are useful in direction finding and radar as their angular with is much smaller than that of the maxima.
Nulling techniques are many - you can turn the antenna and observe the signal level- as it passes through the null, it drops often to the noise level. Instead of mechanically moving the antenna (s), there are many electronic means to move the antenna pattern.
SNR is defined for the complete radio link. You need to know the EIRP of the signal source, propagation loss and receiver antenna gain defined for the main-lobe maximum. The signal drop to the null level often goes to receiver noise floor, so you need to know receiver noise figure and the thermal background toward which antenna null is pointing. Often plus a possible RF interference. At null the SNR may be zero or less.

 

[chuckey]

As an example the commercial AM station(Capital Radio), share the same frequency as do other radio stations. The aerial array is a four mast just north of London, one mast is 6" (150mm) off line. Each mast is fed with a specific amplitude and phase of its RF. The result is that there are four > 60 dB nulls in its radiation pattern so it does not interfere with the other co-channel stations.
Frank