Antenna Arrays

Antenna arrays principles and properties are discussed using an interactive applet.

Antenna arrays are formed by assembling identical (in most cases) radiating elements such as dipoles for example. In the diagram below is shown an antenna array with its elements along the z axis such that the distance between each two successive elements is equal to d.

elements of array antenna along z axis

Antenna arrays are characterized by their array factor which is given by the formula

formula for array factor

where
formula for Psi
N the number of elements making the array, k = 2Pi / wavelength , polar angle theta is the polar angle and phase beta is the difference of phase between any two successive elements forming the array.

The main objective of the tutorial below is to explore how each of the parameters N, d and phase beta affect the radiating pattern of the array.


Interactive Tutorial

APPLET

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1 - Start the applet by clicking on the button "click here to start". On the left panel, you may use any of the sliders to change N the number of elements making the array, d the distance between the elements and the phase phase beta.

2 - Set d = 0.25 (this 0.25*wavelength) ,
phase beta to 0 and increase N slowly. Note that the array is more directional.

End-Fire Array

3 - Set N = 10, d = 0.25 (this is 0.25*wavelength) and
phase beta = kd = 2*Pi*0.25 = 0.5Pi. The main beam (maximum radiation) is directed toward polar angle theta = 180 degrees along the z axis which is also the axis of the array. If you change phase beta to -0.5Pi, the main beam is directed toward 0 degrees along the z axis. For these values of phase beta we have end-fire radiation.

Broadside Array

4 - Set N = 10, d = 0.25 (this 0.25*wavelength) and
phase beta = 0 . The main beam (maximum radiation) is directed toward polar angle theta = 90 degrees normal to the z axis which is also the axis of the array. For this value of phase beta we have broadside radiation.

Change Phase For Scanning

5 - Set N = 10, d = 0.25 (this 0.25*wavelength) and change
phase beta slowly starting from 0. Note that the direction of maximum radiation changes. The maximum radiation can be oriented in any direction. This is the basic principle of electronic scanning using antenna arrays.


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