Fractal Antennas
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What is a fractal antenna?
To understand fractal antennas we must first understand what a fractal is. The term fractal was first coined by Benoit Mandlebrot in 1983 , which is used to classify a structure
whose dimensions are not whole numbers. A known property of fractal geometry is a figure can have an infinite length while fitting in a finite volume.
An electromagnetic radiators characteristics depend on the electrical length of the structure. With this in mind, we can use fractal geometry properties to increase the
electrical length of an antenna and keep its volume the same simultaneously. Interestingly enough , there are an infinite number of geometric designs that could be used for
a fractal antenna.
A noticeable feature of a fractal antenna is its ability to be resonant on more than a single band. The fractal concept can also be used to reduce the size of an antenna , some
good examples of this include the follow types of antennas:
-Koch dipole
-Koch monopole
-Koch loop
-Minkowski loop
It can also be used to achieve multiple bandwidth and increase bandwidth of a single band due to similarity in geometry. Some examples of this include:
-Sierpinski dipole
-Cantor slot patch
-fractal tree dipole.
Fractal Antenna Designs
The simplest example of a fractal geometry antenna is demonstrated by Von Koch. The method used to generate this shape is to repeatedly replace a line
segment with the following 4 line segments. The process starts with a single line , The first iterations are shown in the figure below.
There is currently ongoing research to develop low profile yet frequency independent wide-band antennas using Fractal geometry. A fundamental
property of a classic antenna is the ability to retain the same shape under certain scaling transformations , this property is shared by fractals.