Antennas Theory for Cat2
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Transcript of Antennas Theory for Cat2
7/31/2019 Antennas Theory for Cat2
http://slidepdf.com/reader/full/antennas-theory-for-cat2 1/3
7/31/2019 Antennas Theory for Cat2
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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
7/31/2019 Antennas Theory for Cat2
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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