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
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.
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.
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.
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.