Frequently Asked Questions On Antenna Theory With Answers -7.


This page contains basic questions and short notes on some of the keywords on antenna theory:


31) Define End fire array?

End fire array is defined as an arrangement in which the principal direction of radiation is coincides with the array axis.

For end fire array δ = - β d
where β = 2Π / λ and d = distance between the elements.


32) What is collinear array?

In this array the antenna elements are arranged coaxially by mounting the elements end to end in straight line or stacking them one over the other with radiation pattern circular symmetry.
Eg. Omnidirectional antenna.


33) What is Parasitic array?

In this array the elements are fed parasitically to reduce the problem of feed line. The power is given to one element from that other elements get by electro magnetic coupling.
Eg. Yagi uda antenna.


34) What is the condition on phase for the end fire array with increased directivity?

When δ = - β d, produces maximum field in the direction φ = 0 but dies not give the maximum directivity. It has been shown by Hansen and woodyard that a large directivity is obtained by increasing the phase change between the sources so that δ = - (βd + π / n ).

This condition will be referred to as the condition for increased directivity.


35) Define array factor?

The normalized value of the total field is given by,
E = ( 1 / n) ( sin (n Ψ / 2) / sin ( Ψ / 2) )

The field is given by the expression E will be referred to as array factor.




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