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Describe what is meant by the term "array antenna". Define the terms "array

factor", "element pattern", and "pattern multiplication".

The "array pattern" or "array factor" is the polar radiation plot of a hypothetical

collection of isotropic sources placed on the array antenna grid or pattern, and each

fed with the same amplitude.

Array factor: The radiation pattern of a collection of isotropes placed on the element

centres and fed with the same amplitudes and phases as are applied to the actual

elements of the array.

The "element pattern" is the pattern of any of the similar elements and does notdepend on the location of the element within the grid.

"Pattern multiplication" can then be used to find the total array antenna polar

radiation pattern, by multiplying the gain of the element by the gain of the array of 

isotropes for every particular direction of propagation. The requirements are that

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the element patterns are all identical, and that the actual currents on the elements

(allowing for inter-element couplings) are used to determine the array factor.

"Pattern multiplication":- point wise multiplication of the "element pattern" by the

"array pattern" to obtain the total radiation pattern for the antenna array.

An active array consists of elements each of which is driven by a physical feed.

Passive arrays have one element actively driven, and the others couple to it

electromagnetically through the near field.

The half power beamwidth is the angular separation between the half power points on the

antenna radiation pattern, where the gain is one half the maximum value. The Half 

Power Beamwidth (HPBW) is the angular separation in which

the magnitude of the radiation pattern decrease by 50% (or -3

dB) from the peak of the main beam. 

Return Loss: Is a way of expressing mismatch. It is the logarithmic ratio measured in dB that

compares the power reflected by the antenna to the power that is fed into the antenna from the

transmission line.

Beamwidth: This is the angular separation from which the

magnitude of the radiation pattern decreases to zero.

Classification of antennas

  Frequency of operation and size

  Directivity: omnidirectional, sectorial or directive 

  Physical construction: 

  Application: point-to-point or point-to-multipoint 

BENEFITS OF ANTENNA TILTING

  Minimize interference → lower noise floor → increase capacity

  Ensures a dominant pilot signal in handover regions

  Improve Call Success Rate in terms of Accessibility

  Reduce dropped call rate

  Control coverage more effectively that changing pilot power