yagi uda antennaantenna documentation

7/29/2019 yagi uda antennaAntenna Documentation

1/14

School of Electrical, Electronics

And Computer Engineering

Communications 3

Transmission Media and antenna System

7 Element Yagi with Folded Dipole

SUBMITTED BY:

Balcos, Daniel LuisNavarro, Marc ErnestQuilatan III, Crisostomo

ECE123 B14


2/14

December 12, 2012

Engr. Flordeliza ValienteInstructorSchool of EE-ECE-CpE

Mapa Institute of TechnologyMuralla Street

Intramuros, Manila

To Engr. Flordeliza Valiente:

We are submitting our report entitled 7-Element Yagi with FoldedDipole and our antenna design as a partial fulfillment of theCommunications 3 Lecture course requirement.

The main purpose of this report is to apply our knowledge ofantennas specifically the Yagi-Uda array and folded dipole tocreate a 7-element Yagi antenna wherein the folded dipole willserve as its driven element.

In this regard, we would like to extend our gratitude for giving usthis project which equipped us in designing and making anantenna.

We hope that this report will meet your approval.

Respectfully yours,

ECE123 / B14


3/14

Balcos, Daniel Luis B.Navarro, Marc Ernest S.Quilatan III, Crisostomo

Theories and Principles

A Yagi array, commonly known simply as a Yagi antenna, is

a directional antenna consisting of a driven element (typically a

dipole or folded dipole) and additional parasitic elements (usually

a so-called directors and one or more reflector). In this antenna

assigned to the group, it can be seen that there are five directors,

one feed element which is the folded dipole and also a reflector

which is comprises the 7-element yagi antenna with folded dipole.

Yagi antennas are directional along the axis perpendicular to

the dipole in the plane of the elements, from the reflector toward

the driven element and the director(s). Typical spacings between

elements vary from about 1/10 to 1/4 of a wavelength,

depending on the specific design. The lengths of the directors are

smaller than that of the driven element, which is smaller than

that of the reflector(s) according to an elaborate designprocedure. These elements are usually parallel in one plane,

supported on a single crossbar known as a boom.

The bandwidth of a Yagi antenna refers to the frequency

range over which its directional gain and impedance match are

preserved to within a stated criterion. The Yagi array in its basic

form is very narrowband, with its performance already

compromised at frequencies just a few percent above or below itsdesign frequency. However using larger diameter conductors,

among other techniques, the bandwidth can be substantially

extended.
http://en.wikipedia.org/wiki/Directional_antennahttp://en.wikipedia.org/wiki/Dipole_antennahttp://en.wikipedia.org/wiki/Folded_dipolehttp://en.wikipedia.org/wiki/Parasitic_elementhttp://en.wikipedia.org/wiki/Bandwidth_%28signal_processing%29http://en.wikipedia.org/wiki/Bandwidth_%28signal_processing%29http://en.wikipedia.org/wiki/Parasitic_elementhttp://en.wikipedia.org/wiki/Folded_dipolehttp://en.wikipedia.org/wiki/Dipole_antennahttp://en.wikipedia.org/wiki/Directional_antenna


4/14

The driven element of a Yagi is the equivalent of a center-

fed, half-wave dipole antenna. Parallel to the driven element, and

approximately 0.2 to 0.5 wavelength on either side of it, are

straight rods or wires called reflectors and directors. A reflector is

placed behind the driven element and is slightly longer than 1/2

wavelength; a director is placed in front of the driven element

and is slightly shorter than 1/2 wavelength. A typical Yagi has

one reflector and one or more directors. The antenna propagates

electromagnetic field energy in the direction running from the

driven element toward the director(s), and is most sensitive to

incoming electromagnetic field energy in this same direction.

The Yagi antenna not only has a unidirectional radiation andresponse pattern, but it concentrates the radiation and response.

The more directors a Yagi has, the greater the so-called forward

gain. As more directors are added to a Yagi, it becomes longer.

Some Yagi antennas have as many as 10 or even 12 directors in

addition to the driven element and one reflector. Long Yagis are

rarely used below 50 MHz, because at these frequencies the

structure becomes physically unwieldy.

Figure 1: Basic Elements of a Yagi Antenna
http://searchmobilecomputing.techtarget.com/definition/dipole-antennahttp://searchcio-midmarket.techtarget.com/definition/electromagnetic-fieldhttp://searchcio-midmarket.techtarget.com/definition/electromagnetic-fieldhttp://searchcio-midmarket.techtarget.com/definition/electromagnetic-fieldhttp://searchcio-midmarket.techtarget.com/definition/electromagnetic-fieldhttp://searchmobilecomputing.techtarget.com/definition/dipole-antenna


5/14

The Yagi antenna consists of a single 'feed' or 'driven'

element, typically a dipole or a folded dipole antenna. This is the

only member of the above structure that is actually excited (a

source voltage or current applied). The rest of the elements are

parasitic - they reflect or help to transmit the energy in a

particular direction. The length of the feed element is given in

Figure 1 as F. The feed antenna is almost always the second from

the end, as shown in Figure 1. This feed antenna is often altered

in size to make it resonant in the presence of the parasitic

elements (typically, 0.45-0.48 wavelengths long for a dipole

antenna).

The element to the left of the feed element in Figure 1 is thereflector. The length of this element is given as R and the

distance between the feed and the reflector is SR. The reflector

element is typically slightly longer than the feed element. There is

typically only one reflector; adding more reflectors improves

performance very slightly. This element is important in

determining the front-to-back ratio of the antenna.

Having the reflector slightly longer than resonant serves twopurposes. The first is that the larger the element is, the better of

a physical reflector it becomes.

Secondly, if the reflector is longer than its resonant length,

the impedance of the reflector will be inductive. Hence, the

current on the reflector lags the voltage induced on the reflector.The director elements (those to the right of the feed in Figure 1)

will be shorter than resonant, making them capacitive, so that

the current leads the voltage. This will cause a phase distribution

to occur across the elements, simulating the phase progression of

a plane wave across the array of elements. This leads to the
http://www.antenna-theory.com/antennas/dipole.phphttp://www.antenna-theory.com/antennas/foldeddipole.phphttp://www.antenna-theory.com/definitions/resonant.phphttp://www.antenna-theory.com/definitions/fronttobackratio.phphttp://www.antenna-theory.com/definitions/fronttobackratio.phphttp://www.antenna-theory.com/definitions/resonant.phphttp://www.antenna-theory.com/antennas/foldeddipole.phphttp://www.antenna-theory.com/antennas/dipole.php


6/14

array being designated as a travelling wave antenna. By choosing

the lengths in this manner, the Yagi-Uda antenna becomes an

end-fire array - the radiation is along the +y-axis as shown in

Figure 1.

Figure 2: Example of a 7-Element Yagi-Uda with Folded Dipole

It can be seen on figure 2 an example of a 7-element yagi-

uda with a folded dipole as a driven element. It consists of 5

directors, a reflector and a driven element which is a folded

dipole. The path of the forward direction is in the path where the

directors are placed.


7/14

Design Considerations and Descriptions

The design of the antenna is limited to an operating

frequency of 174MHz up to 890MHz. The operating frequency of

the antenna is computed to be 394MHz, while the wavelength ofthe antenna is 0.76m. The length of the folded dipole is computed

by getting half of the wavelength of the antenna which is 38.1cm,

while the length of the antenna reflector is 41.9cm.

The length of the first director is 34.3cm, the second director

is 32.6cm, the third director is 30.9cm, and the fourth director is

29.2cm and lastly the fifth director which is 27.5cm. The group

had observed a normal spacing of 0.1 which is 7.5cm. The totallength rf the antenna boom length is 50cm.


8/14

Design Calculations and Limitations

fc174890 393.52255

c

fc

3x108ms

393.52255h 0.76235 m

lfolded dipole

2

0.76235 m

20.38118 m 38.1 cm

lreflector.55.41929 m 41.9 cm

Directors:

ldir1.450.34306 m 34.3 cm

ldir2.95ldir1 .950.343060.32591 m 32.6 cm

ldir3.90ldir1 .900.343060.30875 m 30.9 cm

ldir4.85ldir1 .850.343060.2916 m 29.2 cm

ldir5.80ldir1 .800.343060.27445 m 27.5 cm

0.10.07624 m 7.5 cm

(n-1)(7-1)0.152470.45744 m 0.5 m


9/14

Antenna Diagram

7.6cm

7.6cm

7.6cm

7.6cm

7.6cm

7.6cm

27.5 cm

29.2 cm

30.9 cm

32.6 cm

34.3 cm

38.1 cm

41.9 cm

50 cm


10/14

Pictures


11/14


12/14


13/14

List of Materials

Aluminun Tube

Boom

Boom Cap

Screws

Coaxial Cable (2 meters)

80.00 Php

Balun


14/14

Copy of Receipts

yagi uda antennaantenna documentation

Documents