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Yagi

Antenna

Tutorial

Copyright K7JLT 1

Yagi: The Man & Developments

• In the 1920’s two Japanese electrical engineers, Hidetsugu

Yagi and Shintaro Uda at Tohoku University in Sendai Japan,

investigated ways to improve transmitted short wave signals.

• The investigation started with what we now call a dipole

antenna.

• As the investigation continued it was found that additional wire

elements could improve the strength of the transmitted signal.

• The resulting antenna received a Japanese patent in 1926 and

a U.S. patented in 1932.

• This antenna is now known as a Yagi. One of the few

electronic devises that is known by the inventors name.

• Hidetsugu Yagi authored many papers and received patents in

microwave power generation before his death in 1976. Copyright K7JLT 2

Yagi Antennas

What’s a Yagi Antenna?

• As we have learned a Yagi starts with a dipole.

• A Yagi antenna then adds additional elements that

uses parasitic coupling to the dipole to increase

antenna gain.

• A Yagi antenna has at least 1 driven and 1 or more

un-driven elements.

• All Yagi elements are parallel to one another.

Copyright K7JLT 3

Yagi Antennas

What’s parasitic coupling?

• Parasitic coupling is where a antenna element

receives energy from a driven element (dipole) and

re-radiates this energy.

• The act of receiving of energy from the driven element

is known is also known as mutual coupling where a

two-way influence occurs between elements.

• The element diameter, length and distance between

elements effects the amount coupling and radiation.

• Elements longer than the driven element are called

reflectors and shorter elements are called directors.

Copyright K7JLT 4

Yagi Designs

There are thousands of Yagi Designs, so for

consistency in this presentation, the ARRL Antenna

Handbook 21st Edition Medium Duty Yagi’s designed

by N6BV have been chosen.

These Yagi were optimized for Gain, Front-to-Rear

Ratio and Bandwidth allowing consistency between

antennas for comparison.

Copyright K7JLT 5

First let’s look at the relation

between the Yagi Antenna and

the ground, where the antenna

is mounted on a tower of

variable height.

Copyright K7JLT 6

2 Element 20 Meter Yagi

Copyright K7JLT 7

Boom Length 8 Foot


1/2

3/4

1

1 1/4

1 1/2

1 3/4

Copyright K7JLT 8

20’ on 20 Meters


1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 20 Feet

Copyright K7JLT 9


1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 30 Feet

Copyright K7JLT 10


1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 40 Feet

Copyright K7JLT 11


1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 50 Feet

Copyright K7JLT 12


1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 60 Feet

Copyright K7JLT 13


1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 70 Feet

Copyright K7JLT 14


1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 80 Feet

Copyright K7JLT 15


Copyright K7JLT 16

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 90 Feet


Copyright K7JLT 17

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet


Copyright K7JLT 18

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 20 Feet

40 Feet

60 Feet

80 Feet

and 100 Feet

SWR of Yagi @ 100 ft.

Yagi at each height from

20 to 100 feet


Copyright K7JLT 19

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet

With Max Dipole @ 37 Feet

Gain 11.52 dBi @ 9.7⁰

3 dB EL BW 10⁰


Gain 11.52 dBi @ 9.7⁰

3 dB AZ BW 69.8⁰

F/B 11.95 dB

Copyright K7JLT 20


Copyright K7JLT 21

Boom Length 16 Feet


Copyright K7JLT 22

20’ on 20 Meters

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 23

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 20 Feet


Copyright K7JLT 24

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 30 Feet


Copyright K7JLT 25

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 40 Feet


Copyright K7JLT 26

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 50 Feet


Copyright K7JLT 27

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 60 Feet


Copyright K7JLT 28

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 70 Feet


Copyright K7JLT 29

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 80 Feet


Copyright K7JLT 30

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 90 Feet


Copyright K7JLT 31

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet


Copyright K7JLT 32

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 20 Feet

40 Feet

60 Feet

80 Feet

and 100 Feet


20 to 100 feet


Copyright K7JLT 33

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet


Gain 12.67 dBi @ 9.6⁰

3 dB EL BW 9.9⁰


Gain 12.67 dBi @ 9.6⁰

3 dB Az BW 66.6⁰

F/B 35.7 dB

Copyright K7JLT 34


Copyright K7JLT 35

Boom Length 26 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


36

20’ on 20 Meters

Copyright K7JLT

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 37

At 20 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 38

At 30 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 39

At 40 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 40

At 50 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 41

At 60 Feet


Copyright K7JLT 42

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 70 Feet


Copyright K7JLT 43

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 80 Feet


Copyright K7JLT 44

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 90 Feet


Copyright K7JLT 45

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet


Copyright K7JLT 46

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 20 Feet

40 Feet

60 Feet

80 Feet

and 100 Feet


20 to 100 feet


Copyright K7JLT 47

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet


Gain 13.94 dBi @ 10⁰

3 dB EL BW 9.9⁰


Gain 13.94 dBi @ 10⁰

3 dB AZ BW 61.7⁰

F/B 21.17 dB

Copyright K7JLT 48


Copyright K7JLT 49

Boom Length 48 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 50

20’ on 20 Meters

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 51

At 20 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 52

At 30 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 53

At 40 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 54

At 50 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 55

At 60 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 56

At 70 Feet


Copyright K7JLT 57

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 80 Feet


Copyright K7JLT 58

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 90 Feet


Copyright K7JLT 59

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet


Copyright K7JLT 60

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 20 Feet

40 Feet

60 Feet

80 Feet

and 100 Feet


20 to 100 feet


Copyright K7JLT 61

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet


Gain 15.84 dBi @ 10⁰

3 dB EL BW 9.9⁰


Gain 15.84 dBi @ 10⁰

3 dB AZ BW 52.0⁰

F/B 27.9 dB

Copyright K7JLT 62


Copyright K7JLT 63

Boom Length 80 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 64

20’ on 20 Meters


Copyright K7JLT 65

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 20 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 66

At 30 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 67

At 40 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 68

At 50 Feet

1/2

3/4

1

1 1/4

1 1/2

1 3/4


Copyright K7JLT 69

At 60 Feet


Copyright K7JLT 70

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 70 Feet


Copyright K7JLT 71

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 80 Feet


Copyright K7JLT 72

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 90 Feet


Copyright K7JLT 73

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet


Copyright K7JLT 74

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 20 Feet

40 Feet

60 Feet

80 Feet

and 100 Feet


20 to 100 feet


Copyright K7JLT 75

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet


Gain 17.24 dBi @ 9⁰

3 dB EL BW 9.8⁰


Gain 17.24 dBi @ 9⁰

3 dB AZ BW 45⁰

FB 23 dB

Copyright K7JLT 76

Elevation Angle for 20 Meter Yagi’s @ 100 Feet

6 Element

Gain 17.2 dBi @ 9⁰

3 dB Az BW 9.8⁰

Copyright K7JLT 77

5 Element

15.8 Gain dBi @ 10⁰

3 dB Az BW 9.9⁰

4 Element

Gain 13.9 dBi @ 10⁰

3 dB Az BW 9.9⁰

3 Element

Gain 12.7 dBi @ 10⁰

3 dB Az BW 9.9⁰

2 Element

Gain 11.5 dBi @ 10⁰

3 dB Az BW 10⁰

What is going

on?

Remember from the

Dipole Tutorial #2 how

antenna lobs changed as

elevation increased?

Copyright K7JLT 78

Here’s a quick review

of the Dipole Tutorial

height slides.

Copyright K7JLT 79

1/4

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Radiation Pattern

Copyright K7JLT

Radiation Pattern

1/4

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Copyright K7JLT

1/4

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Radiation Pattern

Copyright K7JLT

Radiation Pattern

1/4

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Copyright K7JLT

1/4

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Radiation Pattern

Copyright K7JLT

1/4

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Dipole Radiation Pattern

Copyright K7JLT

1/4

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Dipole Radiation Pattern

Copyright K7JLT

Does this lob behavior look similar to

the Yagi lobs?


Copyright K7JLT 96

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet

Dipole @ 100 Feet

It’s a Match!


Copyright K7JLT 97

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet

Dipole @ 100 Feet

It’s a Match!


Copyright K7JLT 98

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet

Dipole @ 100 Feet

It’s a Match!


Copyright K7JLT 99

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet

Dipole @ 100 Feet

It’s a Match!


Copyright K7JLT 100

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 100 Feet

Dipole @ 100 Feet

It’s a Match!

So what is happening?

Copyright K7JLT 101

The Free space

Antenna Pattern

+

Ground

Reflection

=

Reflected Antenna Pattern

Yagi General Rules of Thumb • Yagi antennas have similar radiation elevation lob

patterns for a single height, just the gain of the

main lob changes with the number of elements.

Copyright K7JLT 102

What happens to the antenna

patterns on different frequency

bands?

Copyright K7JLT 103


Copyright K7JLT 104

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 67 Feet


Copyright K7JLT 105

1/2

3/4

1

1 1/4

1 1/2

1 3/4

20 Meter at 100 Feet

15 Meter at 67 Feet


Copyright K7JLT 106

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 50 Feet


Copyright K7JLT 107

1/2

3/4

1

1 1/4

1 1/2

1 3/4

20 Meter at 100 Feet

10 Meter at 50 Feet




• When height is measured in wavelengths, there is

minimal differences between elevation lobs of

Yagis with the same number of elements on

different bands.

Copyright K7JLT 108

What about the Azimuth

Pattern?

Copyright K7JLT 109

Max. Azimuth for 20 Meter Yagi’s @ 100 Feet

Copyright K7JLT 110

6 Element Yagi

Gain 17.24 dBi @ 9.4⁰

3 dB AZ BW 45⁰

FB 23 dB

5 Element Yagi

Gain 15.84 dBi @ 9.5⁰

3 dB AZ BW 52.0⁰

F/B 28 dB

4 Element Yagi

Gain 13.94 dBi @ 9.5⁰

3 dB AZ BW 61.7⁰

F/B 21 dB

3 Element Yagi

Gain 12,67 dBi @ 9.5⁰

3 dB AZ BW 66.6⁰

F/B 35 dB

2 Element

Gain 11.52 dBi @ 9.6⁰

3 dB AZ BW 69.8⁰

F/B 11.95 dB







different bands.

• The primary Azimuth Lob narrows as additional

elements are added to the array.

Copyright K7JLT 111

Yagi Azimuth Pattern From 20 to100 Feet

Copyright K7JLT 112

6 Element Yagi @ 100 Feet

Gain 17.24 dBi @ 9.4⁰

3 dB AZ BW 45⁰

FB 23 dB

80 Feet

60 Feet

40 Feet

20 Feet







different bands.

• The primary Azimuth Lob narrows as additional

elements are added to the array.

• As the height of a Yagi increases the Azimuth Lob broadens.

Copyright K7JLT 113

Yagi Gain as a Function of Boom Length

Copyright K7JLT 114

5 Element Yagi @ 100 Feet

48Ft Boom 15.79dBi

44Ft Boom 15.69dBi

40Ft Boom 15.12dBi

34Ft Boom 14.82dBi

Yagi Gain

Copyright K7JLT 115

We have seen that Yagi Gain increases

as the boom length is increased.

Is there some rule of thumb equating

boom length to gain?

I looked at the gain vs. boom length in

wavelengths for 105 different Yagi’s

designed for 40 meters up to 70

centimeters and here is the result.

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

Gain vs. Boom Length in

Wavelengths

Copyright K7JLT 116

Boom Length in Wavelengths

Ga

in d

Bi

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

16-40 Elements

15 Elements

14 Elements

13 Elements

12 Elements

11 Elements

10 Elements

9 Elements

8 Elements

7 Elements

6 Elements

5 Elements

4 Elements

3 Elements

2 Elements

Dipole

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00


Wavelengths

Copyright K7JLT 117


Ga

in d

Bi

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

16-40 Elements

15 Elements

14 Elements

13 Elements

12 Elements

11 Elements

10 Elements

9 Elements

8 Elements

7 Elements

6 Elements

5 Elements

4 Elements

3 Elements

2 Elements

Dipole

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00


Wavelengths

Copyright K7JLT 118


Ga

in d

Bi

2.9 dB

6 to 12 λ ≈ 2.9 dB

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00


Wavelengths

Copyright K7JLT 119


Ga

in d

Bi

2.9 dB

6 to 12 λ ≈ 2.9 dB

5 to 10 λ ≈ 2.9 dB

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00


Wavelengths

Copyright K7JLT 120


Ga

in d

Bi

2.9 dB

6 to 12 λ ≈ 2.9 dB

5 to 10 λ ≈ 2.9 dB

4 to 8 λ ≈ 2.9 dB

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00


Wavelengths

Copyright K7JLT 121


Ga

in d

Bi

2.9 dB 3 to 6 λ ≈ 2.9 dB

6 to 12 λ ≈ 2.9 dB

5 to 10 λ ≈ 2.9 dB

4 to 8 λ ≈ 2.9 dB

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00


Wavelengths

Copyright K7JLT 122


Ga

in d

Bi

2.9 dB 2 to 4 λ ≈ 2.9 dB

3 to 6 λ ≈ 2.9 dB

6 to 12 λ ≈ 2.9 dB

5 to 10 λ ≈ 2.9 dB

4 to 8 λ ≈ 2.9 dB

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

20.00

21.00

22.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00


Wavelengths

Copyright K7JLT 123


Ga

in d

Bi

2.9 dB 1 to 2 λ ≈ 2.9 dB

2 to 4 λ ≈ 2.9 dB

3 to 6 λ ≈ 2.9 dB

6 to 12 λ ≈ 2.9 dB

5 to 10 λ ≈ 2.9 dB

4 to 8 λ ≈ 2.9 dB

2.9 dB

Yagi General Rules of Thumb

• As the Yagi Boom Length increases, Antenna gain

increases by ≈ 3dB for every doubling of length.

Copyright K7JLT 124

(Continued)

Maximizing Yagi Gain

Copyright K7JLT 125

Free Space Gain = 7.69 dBi

Front-to-Back Ratio = 36.0 dB


Copyright K7JLT 126




Copyright K7JLT 127




Copyright K7JLT 128




Copyright K7JLT 129




Copyright K7JLT 130




Copyright K7JLT 131



up from 7.69 dBi

down from 36 dB


• As the Yagi Boom Length increases, Antenna gain

increases by about 2.9 dB for every doubling of

length.

• Increasing Gain in an optimized Yagi will

compromises other parameter such as Front-To-

Back ratio.

Copyright K7JLT 132

(Continued)

Can we get more gain by stacking two

Yagis and what else happens?

Copyright K7JLT 133

Here’s two stacked Yagi’s

Copyright K7JLT 135

Two 5 Element 20 Meter Yagi’s

Copyright K7JLT 136

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 40 Feet

At 80 Feet

Antennas fed in phase with equal power


Copyright K7JLT 137

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 45 Feet

At 90 Feet


16.85 dBi @ 12º


Copyright K7JLT 138

1/2

3/4

1

1 1/4

1 1/2

1 3/4

At 50 Feet

At 100 Feet


Gain 17.08 dBi @ 11º

F/B decreased ≈ 11 dB

Minor Lobes

Decreased


• As the Yagi Boom Length is increased Antenna

gain increases.

• Increasing Gain in an optimized Yagi always

compromises some other parameter such as

Front-To-Back ratio.

• Adding a second identical parallel Yagi increases

gain a small amount and changes the pattern.

Copyright K7JLT 140

(Continued)

If we need radiation at a

different angle, can we just use

one of the antennas?

Copyright K7JLT 141

Let’s Look at two stacked Yagi’s

when only the Top antenna is active

Copyright K7JLT 142


Copyright K7JLT 143

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Not Fed 50 Feet

Fed 100 Feet

With only the top antenna fed

15.35 dBi

@ 9º

13.41dBi

@ 29º

F/B ≈ 18 dB

Let’s Look at two stacked Yagi’s

when only the Bottom antenna is active

Copyright K7JLT 144


Copyright K7JLT 145

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Fed 50 Feet

Not Fed 100 Feet

With only the bottom antenna fed

14.49 dBi

@ 19º

What is happening?

Copyright K7JLT 146

Mutual Coupling is

effecting the antenna

patterns!


• As the Yagi Boom Length is increased Antenna

gain increases.

• Increasing Gain in an optimized Yagi always

compromises some other parameter such as

Front-To-Back ratio.

• Adding a second identical parallel Yagi increases

gain only a small amount but changes the pattern.

• Mutual coupling between two parallel antennas

changes the radiation pattern of each antenna.

Copyright K7JLT 147

(Continued)


Copyright K7JLT 148

1/2

3/4

1

1 1/4

1 1/2

1 3/4

Comparison of

Only Fed 100 Feet

Only Fed 50 Feet

Feeding both 100 & 50 Feet

Good Coverage

of 5º to 30º


• Coverage of a wide range of angles is possible

with multiple antennas even with the occurrence

of mutual coupling.

• Care must be taken when adding other antennas

to a tower containing a Yagi (such as a 40 meter

dipole which also resonates on 15 meters)

because it will distort the Yagi’s antenna pattern.

Copyright K7JLT 149

(Continued)

Copyright K7JLT 150

End of Tutorial

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