Yagi Antenna Tutorial. Copyright K7JLT 1

Yagi Antenna Tutorial Copyright K7JLT

Yagi: The Man & Developments In the 920 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 926 and a U.S. patented in 932. 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 976. 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 driven and 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 2 st 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 Boom Length 8 Foot Copyright K7JLT 7

2 Element 20 Meter Yagi 20 on 20 Meters /4 /2 Copyright K7JLT 8

2 Element 20 Meter Yagi At 20 Feet /4 /2 Copyright K7JLT 9

2 Element 20 Meter Yagi At 30 Feet /4 /2 Copyright K7JLT 0

2 Element 20 Meter Yagi At 40 Feet /4 /2 Copyright K7JLT

2 Element 20 Meter Yagi At 50 Feet /4 /2 Copyright K7JLT 2

2 Element 20 Meter Yagi At 60 Feet /4 /2 Copyright K7JLT 3

2 Element 20 Meter Yagi At 70 Feet /4 /2 Copyright K7JLT 4

2 Element 20 Meter Yagi At 80 Feet /4 /2 Copyright K7JLT 5

2 Element 20 Meter Yagi At 90 Feet /4 /2 Copyright K7JLT 6

2 Element 20 Meter Yagi At 00 Feet /4 /2 Copyright K7JLT 7

2 Element 20 Meter Yagi SWR of Yagi @ 00 ft. Yagi at each height from 20 to 00 feet At 20 Feet 40 Feet 60 Feet 80 Feet and 00 Feet /4 /2 Copyright K7JLT 8

2 Element 20 Meter Yagi At 00 Feet With Max Dipole @ 37 Feet Gain.52 dbi @ 9.7⁰ 3 db EL BW 0⁰ /4 /2 Copyright K7JLT 9

2 Element 20 Meter Yagi Gain.52 dbi @ 9.7⁰ 3 db AZ BW 69.8⁰ F/B.95 db Copyright K7JLT 20

3 Element 20 Meter Yagi Boom Length 6 Feet Copyright K7JLT 2

3 Element 20 Meter Yagi 20 on 20 Meters /4 /2 Copyright K7JLT 22

3 Element 20 Meter Yagi At 20 Feet /4 /2 Copyright K7JLT 23

3 Element 20 Meter Yagi At 30 Feet /4 /2 Copyright K7JLT 24

3 Element 20 Meter Yagi At 40 Feet /4 /2 Copyright K7JLT 25

3 Element 20 Meter Yagi At 50 Feet /4 /2 Copyright K7JLT 26

3 Element 20 Meter Yagi At 60 Feet /4 /2 Copyright K7JLT 27

3 Element 20 Meter Yagi At 70 Feet /4 /2 Copyright K7JLT 28

3 Element 20 Meter Yagi At 80 Feet /4 /2 Copyright K7JLT 29

3 Element 20 Meter Yagi At 90 Feet /4 /2 Copyright K7JLT 30

3 Element 20 Meter Yagi At 00 Feet /4 /2 Copyright K7JLT 3

3 Element 20 Meter Yagi Yagi at each height from 20 to 00 feet At 20 Feet 40 Feet 60 Feet 80 Feet and 00 Feet /4 /2 Copyright K7JLT 32

3 Element 20 Meter Yagi At 00 Feet With Max Dipole @ 37 Feet Gain 2.67 dbi @ 9.6⁰ 3 db EL BW 9.9⁰ /4 /2 Copyright K7JLT 33

3 Element 20 Meter Yagi Gain 2.67 dbi @ 9.6⁰ 3 db Az BW 66.6⁰ F/B 35.7 db Copyright K7JLT 34

4 Element 20 Meter Yagi Boom Length 26 Feet Copyright K7JLT 35

4 Element 20 Meter Yagi 20 on 20 Meters /4 /2 Copyright K7JLT 36

4 Element 20 Meter Yagi At 20 Feet /4 /2 Copyright K7JLT 37

4 Element 20 Meter Yagi At 30 Feet /4 /2 Copyright K7JLT 38

4 Element 20 Meter Yagi At 40 Feet /4 /2 Copyright K7JLT 39

4 Element 20 Meter Yagi At 50 Feet /4 /2 Copyright K7JLT 40

4 Element 20 Meter Yagi At 60 Feet /4 /2 Copyright K7JLT 4

4 Element 20 Meter Yagi At 70 Feet /4 /2 Copyright K7JLT 42

4 Element 20 Meter Yagi At 80 Feet /4 /2 Copyright K7JLT 43

4 Element 20 Meter Yagi At 90 Feet /4 /2 Copyright K7JLT 44

4 Element 20 Meter Yagi At 00 Feet /4 /2 Copyright K7JLT 45

4 Element 20 Meter Yagi Yagi at each height from 20 to 00 feet At 20 Feet 40 Feet 60 Feet 80 Feet and 00 Feet /4 /2 Copyright K7JLT 46

4 Element 20 Meter Yagi At 00 Feet With Max Dipole @ 37 Feet Gain 3.94 dbi @ 0⁰ 3 db EL BW 9.9⁰ /4 /2 Copyright K7JLT 47

4 Element 20 Meter Yagi Gain 3.94 dbi @ 0⁰ 3 db AZ BW 6.7⁰ F/B 2.7 db Copyright K7JLT 48

5 Element 20 Meter Yagi Boom Length 48 Feet Copyright K7JLT 49

5 Element 20 Meter Yagi 20 on 20 Meters /4 /2 Copyright K7JLT 50

5 Element 20 Meter Yagi At 20 Feet /4 /2 Copyright K7JLT 5

5 Element 20 Meter Yagi At 30 Feet /4 /2 Copyright K7JLT 52

5 Element 20 Meter Yagi At 40 Feet /4 /2 Copyright K7JLT 53

5 Element 20 Meter Yagi At 50 Feet /4 /2 Copyright K7JLT 54

5 Element 20 Meter Yagi At 60 Feet /4 /2 Copyright K7JLT 55

5 Element 20 Meter Yagi At 70 Feet /4 /2 Copyright K7JLT 56

5 Element 20 Meter Yagi At 80 Feet /4 /2 Copyright K7JLT 57

5 Element 20 Meter Yagi At 90 Feet /4 /2 Copyright K7JLT 58

5 Element 20 Meter Yagi At 00 Feet /4 /2 Copyright K7JLT 59

5 Element 20 Meter Yagi Yagi at each height from 20 to 00 feet At 20 Feet 40 Feet 60 Feet 80 Feet and 00 Feet /4 /2 Copyright K7JLT 60

5 Element 20 Meter Yagi At 00 Feet With Max Dipole @ 37 Feet Gain 5.84 dbi @ 0⁰ 3 db EL BW 9.9⁰ /4 /2 Copyright K7JLT 6

5 Element 20 Meter Yagi Gain 5.84 dbi @ 0⁰ 3 db AZ BW 52.0⁰ F/B 27.9 db Copyright K7JLT 62

6 Element 20 Meter Yagi Boom Length 80 Feet Copyright K7JLT 63

6 Element 20 Meter Yagi 20 on 20 Meters /4 /2 Copyright K7JLT 64

6 Element 20 Meter Yagi At 20 Feet /4 /2 Copyright K7JLT 65

6 Element 20 Meter Yagi At 30 Feet /4 /2 Copyright K7JLT 66

6 Element 20 Meter Yagi At 40 Feet /4 /2 Copyright K7JLT 67

6 Element 20 Meter Yagi At 50 Feet /4 /2 Copyright K7JLT 68

6 Element 20 Meter Yagi At 60 Feet /4 /2 Copyright K7JLT 69

6 Element 20 Meter Yagi At 70 Feet /4 /2 Copyright K7JLT 70

6 Element 20 Meter Yagi At 80 Feet /4 /2 Copyright K7JLT 7

6 Element 20 Meter Yagi At 90 Feet /4 /2 Copyright K7JLT 72

6 Element 20 Meter Yagi At 00 Feet /4 /2 Copyright K7JLT 73

6 Element 20 Meter Yagi Yagi at each height from 20 to 00 feet At 20 Feet 40 Feet 60 Feet 80 Feet and 00 Feet /4 /2 Copyright K7JLT 74

6 Element 20 Meter Yagi At 00 Feet With Max Dipole @ 37 Feet Gain 7.24 dbi @ 9⁰ 3 db EL BW 9.8⁰ /4 /2 Copyright K7JLT 75

6 Element 20 Meter Yagi Gain 7.24 dbi @ 9⁰ 3 db AZ BW 45⁰ FB 23 db Copyright K7JLT 76

Elevation Angle for 20 Meter Yagi s @ 00 Feet 5 Element 5.8 Gain dbi @ 0⁰ 3 db Az BW 9.9⁰ 4 Element Gain 3.9 dbi @ 0⁰ 3 db Az BW 9.9⁰ 3 Element Gain 2.7 dbi @ 0⁰ 3 db Az BW 9.9⁰ 2 Element Gain.5 dbi @ 0⁰ 3 db Az BW 0⁰ 6 Element Gain 7.2 dbi @ 9⁰ 3 db Az BW 9.8⁰ What is going on? Copyright K7JLT 77

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

Radiation Pattern /4 Copyright K7JLT /2 /4

Dipole Radiation Pattern /4 Copyright K7JLT /2 /4

Dipole Radiation Pattern Does this lob behavior look similar to the Yagi lobs? /4 Copyright K7JLT /2 /4

2 Element 20 Meter Yagi At 00 Feet Dipole @ 00 Feet It s a Match! /4 /2 Copyright K7JLT 96

3 Element 20 Meter Yagi At 00 Feet Dipole @ 00 Feet It s a Match! /4 /2 Copyright K7JLT 97

4 Element 20 Meter Yagi At 00 Feet Dipole @ 00 Feet It s a Match! /4 /2 Copyright K7JLT 98

5 Element 20 Meter Yagi At 00 Feet Dipole @ 00 Feet It s a Match! /4 /2 Copyright K7JLT 99

6 Element 20 Meter Yagi At 00 Feet Dipole @ 00 Feet It s a Match! /4 /2 Copyright K7JLT 00

So what is happening? The Free space Antenna Pattern + Ground Reflection = Reflected Antenna Pattern Copyright K7JLT 0

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 02

What happens to the antenna patterns on different frequency bands? Copyright K7JLT 03

6 Element 5 Meter Yagi At 67 Feet /4 /2 Copyright K7JLT 04

6 Element 5 Meter Yagi 20 Meter at 00 Feet 5 Meter at 67 Feet /4 /2 Copyright K7JLT 05

6 Element 5 Meter Yagi At 50 Feet /4 /2 Copyright K7JLT 06

6 Element 0 Meter Yagi 20 Meter at 00 Feet 0 Meter at 50 Feet /4 /2 Copyright K7JLT 07

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. 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 08

What about the Azimuth Pattern? Copyright K7JLT 09

Max. Azimuth for 20 Meter Yagi s @ 00 Feet 5 Element Yagi Gain 5.84 dbi @ 9.5⁰ 3 db AZ BW 52.0⁰ F/B 28 db 4 Element Yagi Gain 3.94 dbi @ 9.5⁰ 3 db AZ BW 6.7⁰ F/B 2 db 3 Element Yagi Gain 2,67 dbi @ 9.5⁰ 3 db AZ BW 66.6⁰ F/B 35 db 2 Element Gain.52 dbi @ 9.6⁰ 3 db AZ BW 69.8⁰ F/B.95 db 6 Element Yagi Gain 7.24 dbi @ 9.4⁰ 3 db AZ BW 45⁰ FB 23 db Copyright K7JLT 0

Yagi Azimuth Pattern From 20 to00 Feet 6 Element Yagi @ 00 Feet Gain 7.24 dbi @ 9.4⁰ 3 db AZ BW 45⁰ FB 23 db 80 Feet 60 Feet 40 Feet 20 Feet Copyright K7JLT 2

Yagi Gain as a Function of Boom Length 5 Element Yagi @ 00 Feet 48Ft Boom 5.79dBi 44Ft Boom 5.69dBi 40Ft Boom 5.2dBi 34Ft Boom 4.82dBi Copyright K7JLT 4

Yagi Gain 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 05 different Yagi s designed for 40 meters up to 70 centimeters and here is the result. Copyright K7JLT 5

Gain dbi Gain vs. Boom Length in Wavelengths 22.00 2.00 6-40 Elements 20.00 5 Elements 9.00 4 Elements 8.00 3 Elements 7.00 2 Elements 6.00 5.00 Elements 4.00 0 Elements 3.00 9 Elements 2.00 8 Elements.00 7 Elements 0.00 9.00 6 Elements 8.00 5 Elements 7.00 4 Elements 6.00 3 Elements 5.00 4.00 2 Elements 3.00 Dipole 2.00 0.00 2.00 4.00 6.00 8.00 0.00 2.00 4.00 Boom Length in Wavelengths Copyright K7JLT 6

Gain dbi Gain vs. Boom Length in Wavelengths 22.00 2.00 20.00 9.00 8.00 2.9 db 7.00 6.00 5.00 4.00 3.00 2.00.00 0.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00 0.00 2.00 4.00 6.00 8.00 0.00 2.00 4.00 Boom Length in Wavelengths 6 to 2 λ 2.9 db Copyright K7JLT 8

Gain dbi Gain vs. Boom Length in Wavelengths 22.00 2.00 20.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00.00 0.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.9 db 2.00 0.00 2.00 4.00 6.00 8.00 0.00 2.00 4.00 Boom Length in Wavelengths 6 to 2 λ 2.9 db 5 to 0 λ 2.9 db Copyright K7JLT 9

Gain dbi Gain vs. Boom Length in Wavelengths 22.00 2.00 20.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00.00 0.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.9 db 2.00 0.00 2.00 4.00 6.00 8.00 0.00 2.00 4.00 6 to 2 λ 2.9 db 5 to 0 λ 2.9 db 4 to 8 λ 2.9 db Boom Length in Wavelengths Copyright K7JLT 20

Gain dbi Gain vs. Boom Length in Wavelengths 22.00 2.00 20.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00.00 0.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.9 db 2 to 4 λ 2.9 db 2.00 0.00 2.00 4.00 6.00 8.00 0.00 2.00 4.00 Boom Length in Wavelengths 6 to 2 λ 2.9 db 5 to 0 λ 2.9 db 4 to 8 λ 2.9 db 3 to 6 λ 2.9 db Copyright K7JLT 22

Yagi General Rules of Thumb (Continued) As the Yagi Boom Length increases, Antenna gain increases by 3dB for every doubling of length. Copyright K7JLT 24

Maximizing Yagi Gain Free Space Gain = 7.69 dbi Front-to-Back Ratio = 36.0 db Copyright K7JLT 25

Maximizing Yagi Gain Free Space Gain = 8.2 dbi Front-to-Back Ratio = 24.5 db Copyright K7JLT 26

Maximizing Yagi Gain Free Space Gain = 8.50 dbi Front-to-Back Ratio = 7.4 db Copyright K7JLT 27

Maximizing Yagi Gain Free Space Gain = 8.80 dbi Front-to-Back Ratio = 3.7 db Copyright K7JLT 28

Maximizing Yagi Gain Free Space Gain = 8.97 dbi Front-to-Back Ratio =.3 db Copyright K7JLT 29

Maximizing Yagi Gain Free Space Gain = 9.00 dbi Front-to-Back Ratio = 9.6 db Copyright K7JLT 30

Maximizing Yagi Gain Free Space Gain = 9.53 dbi up from 7.69 dbi Front-to-Back Ratio = 8.4 db down from 36 db Copyright K7JLT 3

Yagi General Rules of Thumb (Continued) 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 32

Can we get more gain by stacking two Yagis and what else happens? Copyright K7JLT 33

Here s two stacked Yagi s Copyright K7JLT 35

Two 5 Element 20 Meter Yagi s Antennas fed in phase with equal power At 40 Feet At 80 Feet /4 /2 Copyright K7JLT 36

Two 5 Element 20 Meter Yagi s Antennas fed in phase with equal power At 45 Feet At 90 Feet 6.85 dbi @ 2º /4 /2 Copyright K7JLT 37

Two 5 Element 20 Meter Yagi s Antennas fed in phase with equal power At 50 Feet At 00 Feet F/B decreased db Minor Lobes Decreased Gain 7.08 dbi @ º /4 /2 Copyright K7JLT 38

Yagi General Rules of Thumb (Continued) 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 40

If we need radiation at a different angle, can we just use one of the antennas? Copyright K7JLT 4

Let s Look at two stacked Yagi s when only the Top antenna is active Copyright K7JLT 42

Two 5 Element 20 Meter Yagi s With only the top antenna fed Not Fed 50 Feet Fed 00 Feet F/B 8 db 3.4dBi @ 29º 5.35 dbi @ 9º Copyright K7JLT 43 /4 /2

Let s Look at two stacked Yagi s when only the Bottom antenna is active Copyright K7JLT 44

Two 5 Element 20 Meter Yagi s With only the bottom antenna fed Fed 50 Feet Not Fed 00 Feet /4 4.49 dbi @ 9º /2 Copyright K7JLT 45

What is happening? Mutual Coupling is effecting the antenna patterns! Copyright K7JLT 46

Yagi General Rules of Thumb (Continued) 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 47

Two 5 Element 20 Meter Yagi s Comparison of Only Fed 00 Feet Only Fed 50 Feet Feeding both 00 & 50 Feet Good Coverage of 5º to 30º /4 /2 Copyright K7JLT 48

Yagi General Rules of Thumb (Continued) 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 5 meters) because it will distort the Yagi s antenna pattern. Copyright K7JLT 49