An antenna array is a radiating system, which consists of individual radiators and elements. Each of this radiator, while functioning has its own induction field. The elements are placed so closely that each one lies in the neighbouring one’s induction field. Therefore, the radiation pattern produced by them, would be the vector sum of the individual ones. The following image shows another example of an antenna array.
The spacing between the elements and the length of the elements according to the wavelength are also to be kept in mind while designing these antennas.
The antennas radiate individually and while in array, the radiation of all the elements sum up, to form the radiation beam, which has high gain, high directivity and better performance, with minimum losses.
Antenna array types are mainly categorized into four types which are explained as below:
1. Broadside Type
In the broadside antenna array, similar elements are placed in a parallel way all across the line that is normal to the antenna’s axis. This is the widely employed antenna configuration and all the elements are positioned horizontally with similar spacing between them and every element in the array is provided with a current having a similar phase and magnitude levels. When there is excitation to the elements, then the array delivers maximum radiation in the normal direction of the antenna axis, whereas in the other directions less amount is delivered. This forms a bidirectional radiation pattern.
The characteristics of the broadside type of antenna array are:
2. End-Fire Type
The arrangement of elements in the end-fire type is the same as that of the broadside antenna array and the difference occurs in the excitation pattern provided to the end-fire antenna. Here, the elements are provided with 1800 out of phase. This type of arrangement delivers maximum radiation across all the array axis.
The end-fire antenna is excited with current having a similar magnitude level but has phase difference across the line thus creating a unidirectional radiation pattern. It is said that phase differences should vary corresponding to the progressive distance between elements.
The characteristics of the end-fire type of antenna array are:
3. Collinear Type
The name of the antenna itself signifies that the arrangement of different elements is stacked in a single line. The line arrangement can be in the horizontal or vertical directions. The excitation is fed to every element in the antenna having a current with a similar phase and magnitude. The radiation pattern is in the normal direction to the antenna array axis. So, the collinear antenna arrays’ major lobe provides a circular symmetry pattern that enables an omnidirectional radiation pattern.
When the elements are placed at a distance of 0.3 to 0.5λ between them, the array offers maximum gain whereas this directs to constructional and feeding issues. In order to avoid those problems, the elements are closely placed. The directivity of the antenna gets increased when the array length is increased.
The characteristics of the collinear type of antenna array are:
4. Parasitic Type
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