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.
