Radiation pattern refers to the plot of radiation properties of any antenna. Thin linear antennas are similar to dipole antennas with symmetric fed source at the center by a balanced two wire transmission line. Moreover linear antennas have sinusoidal current distribution. We consider the diameter of the antenna d<λ/100, which provides good natural approximation to the current distribution. Current distributions for various antennas are as shown in figure below.
Fig. Current distribution (source: JD kraus, Antenna and propagation, Thanks Gaurav for this photo)
I have plotted the radiation patterns of these antennas with the help of Matlab GUI. The pattern is of electric field is in theta direction. The equation is
This GUI is as shown in the figure below.
Fig. λ/2 antenna
The GUI has facility to choose the antenna size (i.e. length of the antenna, L) = λ/2, 3λ/4, λ, 3λ/2 and 2λ. It plots 3D pattern of chosen antenna as shown in figure above; which is field pattern of λ/2 antenna. The plots of patterns for other antennas are as follows:
Fig. 3λ/4 antenna
Fig. λ antenna
Fig. 3λ/2 antenna
Fig. λ antenna
You can view the source code from here.
(Reference: Antennas and Wave Propagation, JD Kraus, 4th edition)
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