The power when radiated from the antenna has its effect in the near and far field regions.
Let us look at the pattern of energy radiation.
The figure given above shows radiation pattern of a dipole antenna. The energy being radiated is represented by the patterns drawn in a particular direction. The arrows represent directions of radiation.
The radiation patterns can be field patterns or power patterns.
The given figure is a three dimensional radiation pattern for an Omni directional pattern. This clearly indicates the three co-ordinates (x, y, z).
The figures show the Omni directional radiation pattern in H and V planes as explained above. H-plane represents the Horizontal pattern, whereas V-plane represents the Vertical pattern.
To have a better understanding, consider the following figure, which represents the radiation pattern of a dipole antenna.
Here, the radiation pattern has main lobe, side lobes and back lobe.
Example
If the antennas used in radar systems produce side lobes, target tracing becomes very difficult. This is because, false targets are indicated by these side lobes. It is messy to trace out the real ones and to identify the fake ones. Hence, elimination of these side lobes is must, in order to improve the performance and save the energy.
Remedy
The radiated energy, which is being wasted in such forms needs to be utilized. If these minor lobes are eliminated and this energy is diverted into one direction (that is towards the major lobe), then the directivity of the antenna gets increased which leads to antenna’s better performance.
A referential point for all these types of radiation is the isotropic radiation. It is important to consider the isotropic radiation even though it is impractical.
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