Wireless Data Technologies
There are many different types of antennae
currently in use. Each different type is suited to a different
purpose and works best at a particular frequency. These notes
concern the Yagi-Uda antenna and will be concerned with its
characteristics and uses. Generally we refer to this type of
antenna as just a Yagi antenna or array. We will also view the
Yagi antenna from a mathematical perspective.
The Yagi antenna can be used for transmitting or receiving radio
The Yagi-Uda antenna was invented in Japan at Tohoku
Imperial University by Hidetsugu Yagi and Shintaro Uda in 1926
and published his research in English in 1928. Yagi arrays
were used widely in the Second World War because they were
simple to build and directional.
You will very probably be familiar with the shape of a Yagi
antenna. It is the type of antenna that is on the roof of many
houses for television reception.
A standard dipole
antenna picks up signals equally well in all directions. The Yagi
antenna is different from a standard dipole antenna because it is
directional. It is directional along the axis that is at 90
degrees to the dipole in the line of the extra elements. The part
that holds the elements of the Yagi antenna is also known as the
boom or crossbar. This means that you have to point the crossbar
towards the direction of the signal that you are trying to
receive. If you look at the top of a group of houses that have
television antennae installed, you will generally see that the
antennae booms are pointing in the same direction. This tells you
the direction in which the television transmitter is located.
The directionality of a Yagi antenna can be measured in terms of
A typical Yagi may have a gain figure around 3 to 20 dBd.
A Yagi antenna is composed of several different parts. It will
have a dipole which is connected to the coaxial cable and also
several parasitic elements which are not connected to the cabling.
These extra parts will be a reflector and at least one director.
These can be seen in the diagram below.
The dipole is the driven element of this type of antenna. The
dipole will be 1/2 a wavelength in length or λ/2
The reflector lies behind the dipole and is generally 5% longer
than the dipole. It should be λ/10 metres behind the dipole
The directors are progressively shorter than the dipole
by approximately 5% and are λ/10
Other Yagi Antennae
Sometimes you may see an antenna such as that depicted below. This
is sometimes known as a cigar antenna. This is a Yagi, but it is
Inside this may be the following components.
A useful page for the cigar antenna is http://www.pow.za.net/cigar.html
The Yagi is the most commonly used antenna in applications that
operate above 10 MHz. They are simple to construct and have good
Our lab work will be to construct and test a simple Yagi antenna.
We will split into small groups and build one Yagi antenna per
group. This will then be tested in the anechoic chamber in N132.
The antenna will be tested for several factors. Below is an image
of a prototype built and tested in September 2008 at the
University of Greenwich's anechoic chamber facility.
Results and Yagi are shown below.
The results are shown below - click image to enlarge.
Detailed Test Results
For now, we will concentrate on some of the factors of the Yagi
that we need to measure and understand. The book, Wi-Fi Toys - 15
Cool Wireless Projects For Home, Office, And Entertainment (2004)
chapter 2 gives instructions on how to build this antenna using a
lolly stick and some paperclips. An example is shown below.
A small amount of soldering will be required to connect your
antenna to the coaxial cabling to allow it to be tested.
Yagi antennae are directional with high gain and can be
constructed easily. They have been used in applications that
operate over 10 MHz since the Second World War. We will construct
our own and test them with the University's anechoic chamber.
Calculates in Imperial units for a 3 element Yagi
Calculates dimensions for seven element Yagi
for Yagi - allows for number of directors to be chosen etc..
page with many calculation resources for antennae