Antenna Polarization

The polarization of an antenna is the polarization of the wave radiated by the antenna. At a given position, the polarization describes the orientation of the electric field.

Suppose an electromagnetic wave, radiated by an antenna, has an electric field E ( a vector) with two components: E_x and E_y.

We are going to explore the figure traced by the tip of vector E at a given position along the z axis as the time changes.

Let us assume that the components E_x and E_y of electric field E are given by

where a is the amplitude of component E_x and b is the amplitude of component E. Phi is the difference of phase between the two components.

Tutorial using an applet

Press the button below "press here to start". The left is for controlling parameters a, b and Phi and to start or stop the animation. Time t in the expressions giving the electric field is changed by steps or continuously. The electric field vector E changes in magnitude and direction. The extremity of the vector field E describes a curve: This curve defines the polarization.

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1 - Linear polarization

Use the scrollbar to set Phi to 0. Set a = 1 and b = 1. (these values might be set already). Press the button "START/STOP animation". The trace of the field vector E should be linear of the hence this is linear polarization. Change a and b and observe the angle of the segment changing.
The condition for linear polarization is that Phi should take values such as : Phi = n*Pi, where n is an integer. Use different values for Phi = n*Pi and check that the polarization is linear.

2 - Circular polarization

Set a = b = 1 and Phi to 0.5Pi. Press the button "START/STOP animation". The trace is now a circle.
The conditions for circular polarization is that Phi should take values such as : Phi = (n+1)Pi/2. Example: Phi = Pi/2 , 3Pi/2, -Pi/2 ... and a = b. Take different values for Phi and a and b according the stated conditions and check that the polarization is circular.

3 - Elliptical polarization

Set a = b = 1 and Phi to any value other than 0, Pi, 0.5Pi, say 0.7Pi for example. Press the button "START/STOP animation". The trace is now an ellipse.
The conditions for elliptical polarization is that Phi should take values such as : Phi = (n+1)Pi/2. Example: Phi = Pi/2 , 3Pi/2, -Pi/2... Take different values for Phi according the stated conditions and check that the polarization is an ellipse if a is NOT equal to b.

More on antennas antennas and parabolic reflectors.