The electric far field components radiated by a circular aperture antenna are given by

where r is the distance from the antenna to the point of observation, a is the radius of the circular aperture, E_{o} is the constant field over the aperture and k = 2Pi / wavelength.

Two applets can be used to explore the properties such as radiation pattern of circular apertures.
__Radiation Pattern in Polar Coordinates__

The applet below displays the radiation pattern for different values of the radius of the circular aperture and different values of angle Phi.

1 - Click on the button to start the applet.

2 - Use the top slider to increase the radius (relative to wavelength) of the circular aperture. What happens to the radiation pattern?

3- Keep the radius constant and change angle Phi. Any major changes in the radiation pattern?
__Radiation Pattern in Rectangular Coordinates__

The applet below shows the electric field for Phi = 0 (in blue) and for Phi = pi/2 (in red) in rectangular coordinate.

1 - Click on the button to start the applet.

2 - Change the radius of the aperture antenna. What happens to the field distribution and the half power beam width?

More on antennas
antennas and parabolic reflectors.