**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.

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

where
N the number of elements making the **array**, k = 2Pi / wavelength , is the polar angle and 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 affect the radiating pattern of the **array**.

__Interactive Tutorial__

APPLET

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 .

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

__Broadside __**Array**

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

__Change Phase For Scanning__

5 - Set N = 10, d = 0.25 (this 0.25*wavelength) and change 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.

More on antennas
antennas and parabolic reflectors.