Yagi Project

WESLEYAN UNIVERSITY – PHILIPPINES Mabini Extesion, Cabanatuan City

COLLEGE OF ENGINEERING

YAGI – UDA ANTENNA DESIGN Communications – 4

Submitted by: ANGELES, GABRIELLE E. ANGELES, HAROLD V. CARLOS, JOHN FERNANDO CASTRO, KEN AL WAGIE CUDIA, EDUARDO S. GONZALES, JOCELYN GAYE A. FRANCISCO, EFRAIM M. NUÑEZ, GENESIS S. ROBLES, JOMARIE U. VALENCIA, PRINCESS JOY M. BSEcE - 5

Submitted to: ENGR. LEO M. RAMOS Professor

INTRODUCTION

A Yagi – Uda antenna is a linear array consisting of a dipole and two or more parasitic elements: one reflector and one or more directors. The driven element is a half wavelength dipole and is connected to the transmission line. The reflector is a straight aluminium rod approximately 5% longer than the dipole and the director is cut approximately 5% shorter than the driven element. The spacing for the elements ranges from 0.1 to 0.2 wavelength.

The typical directivity of a Yagi – Uda antenna was 7dB to 9dB and in this paper the researcher desired to design a Yagi antenna with a higher directivity gain ranging from 11dB – 14dB. The Yagi – Uda antenna is usually used for VHF television because of its wide bandwidth. And in this design the researchers will also

be

using

the

antenna

for

the

same

improvements with the gain of the antenna.

purpose

but

with

Figure 1 Yagi – Uda Antenna The figure above shows an example of a Yagi – Uda Antenna and its elements.

This

paper

presents

the

proposed

antenna

design

for

television reception. The researchers used a Yagi – Uda antenna as the basis of their design. This paper will also discuss all the computations and basic considerations in making this kind of antenna.

The following computations will be used for the design of the Yagi – Uda Antenna.

DESIGN COMPUTATION: FREQUENCY: 174 – 180 MHz CENTER FREQUENCY:

((174 x 106 + 180 x 106)/2) = 177 MHz

GAIN:

= 14.2dB

WAVELENGTH (λ):

= 3 x 108 / frequency

λ

= 3 x 108 / 177 x 106 = 1.6949 m = 169.49cm

Desired d

= 1.00 cm

Desired D

= 2.50 cm

d/λ

= 1.00/169.49 = 0.000590 cm.

D/λ

= 2.54/169.49 = 0.014986 cm.

Length of Directors (from Table 1 under 14.20dB) Element number 3

= 0.424λ = 71.864 cm.

Element number 4

= 0.424λ = 71.864 cm.

Element number 5

= 0.420λ = 71.186 cm.

Element number 6

= 0.407λ = 68.982 cm.

Element number 7

= 0.403λ = 68.304 cm.

Element number 8

= 0.398λ = 67.457 cm.

Element number 9

= 0.394λ = 66.779 cm.

Element number 10

= 0.390λ = 66.101 cm.

Element number 11

= 0.390λ = 66.101 cm.

Element number 12

= 0.390λ = 66.101 cm.

Element number 13

= 0.390λ = 66.101 cm.

Element number 14

= 0.390λ = 66.101 cm.

Element number 15

= 0.390λ = 66.101 cm.

Length of Reflector (I1/λ)

= 0.475λ = 80.508 cm.

Driven Element Length

= λ/2

= 84.745 cm.

From Figure 2 the ratio of d/ λ was plotted to obtain the uncompensated length of 0.41 λ with the reflector length of 0.471 λ.

Data

below

are

the

values

derived

in

Figure

uncompensated director length. Element number 3

= 0.430λ = 72.881 cm.

Element number 4

= 0.430λ = 72.881 cm.

Element number 5

= 0.426λ = 72.203 cm.

1

for

Element number 6

= 0.413λ = 69.999 cm.

Element number 7

= 0.409λ = 69.321 cm.

Element number 8

= 0.404λ = 68.474 cm.

Element number 9

= 0.400λ = 67.796 cm.

Element number 10-15

= 0.396λ = 67.118 cm.

With the ratio of 0.0149 for D/λ, see Figure 3 to determine the value to be added to compensate the elements length.

The following are the compensated length of the proposed donor antenna for 0.0081 compensated lengths.

Element number 3

= 0.430λ + 0.0081λ = 74.254 cm.

Element number 4

= 0.430λ + 0.0081λ = 74.254 cm.

Element number 5

= 0.426λ + 0.0081λ = 73.576 cm.

Element number 6

= 0.413λ + 0.0081λ = 71.372 cm.

Element number 7

= 0.409λ + 0.0081λ = 70.694 cm.

Element number 8

= 0.404λ + 0.0081λ = 69.847 cm.

Element number 9

= 0.400λ + 0.0081λ = 69.169 cm.

Element number 10-15

= 0.396λ + 0.0081λ = 68.491 cm.

Reflector Length

= 0.471λ + 0.0081λ = 81.203 cm.

Total Boom Length

=

0.308 director spacing x 13 +0.2

=

4.204λ

Table 1 Values of the Elements length of Yagi - Uda Antenna

The Table above shows the optimized uncompensated lengths of parasitic elements for Yagi- Uda antenna. In the table to attain a gain of 12.25 dB, the required elements are 10 directors, 1 reflector and a dipole driven element.

Figure 2 Design Curves to Determine Length of the Elements of Yagi - Uda Antenna.

The figure above shows the increase in optimum length of parasitic elements as a function of metal boom diameter.

Figure 3 Increase in Optimum length of Parasitic Element

Figure 2 shows the increase in optimum length of parasitic elements as a function of metal boom diameter.

Figure 4 Proposed Yagi - Uda Antenna For Television Reception

The figure above shows the proposed 15 elements Yagi - Uda antenna that will be used for television reception. It has the total gain of 14.2dB It has 13 directors, 1 reflector and dipole as driven element.