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Yagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory & Design John Wiley & Sons, 1981, 1998, 2013

Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

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Page 1: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Yagi-Uda (Beam) Antenna

Gary A. Thiele

KD8ZWS (Ex W8RBW)

Co-author of Antenna Theory & Design

John Wiley & Sons, 1981, 1998, 2013

Page 2: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Yagi-Uda (Beam) Antennas

Page 3: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 4: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Outline

• Preliminary Remarks

• Part I Brief history of the Yagi-Uda (Beam)

• Part II Brief personal notes

• Part III A few antenna basics

• Part IV A technical discussion

Note: No equations!

Page 5: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 6: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Book Facts

• 3rd edition currently in print,

3rd printing pending

• 3rd edition to be published in Korean,

Portuguese and maybe Chinese

• Over 1500 equations (but none in this talk!)

• 822 pages, 16 chapters

• 3rd edition pirated on the internet

Page 7: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Part I A Brief History

• Objective: to present some historical facts and early uses of the Yagi-Uda antenna.

Page 8: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Part I A Brief History

• The Yagi-Uda antenna was invented in 1926 in Sendai, Japan by Asst. Prof. Shintaro Uda in colaboration with his mentor Prof. Yagi.

Page 9: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Shintaro Uda

Page 10: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

History – cont.

• Uda initially was tasked to design an oscillator to radiate at 4.4m wavelenth ( ~68 Mhz.)

• For the antenna he used a resonant loop. Then he placed a parasitic loop nearby and observed more directive radiation.

Page 11: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

History – cont.

• Subsequently he replaced the loops with metal rods observing that more rods (now know as directors) increased the field intensity in the desired direction.

• He then undertook a systematic investigation to determine the effect on antenna directivity of changes in length, spacing and geometric arrangement of the parasitic elements.

• The 8 director 68 MHz Yagi-Uda on the next slide is a result of his investigation.

Page 12: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 13: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

History – cont.

• Uda and Yagi jointly published the results of their investigation in 1926 in Japan. There followed a series of papers in the Journal of the IEE Japan (in Japanese).

• U.S. engineers learned of the new antenna at a Tokyo conference in Nov. 1926. This was followed by a classic IEEE journal publication in the U.S. in May 1927 by Yagi and Uda.

• Prof. Yagi visited the U.S. in 1928 giving a number of talks about the antenna further publicizing it.

Page 14: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

History – cont.

• The Yagi-Uda antenna was widely used in WWII radar sets, both by Japan and the Allies.

• Recall, kilowatts of power then could not be generated at centimeter wavelengths. Hence, the use of the Yagi-Uda at meter wavelengths.

• When Japan captured Singapore and the British radar sets, they were at first interested in the Yagi-Uda antennas, not realizing they were invented in Japan in 1926!

Page 15: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 16: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 17: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

History – cont.

• What was needed in WWII was a sufficient power source at centimeter wavelengths to enable the development of airborne radar.

• In 1941 the British developed a cavity magnetron, capable of many kilowatts of power at centimeter wavelengths, and shared it in great secrecy with the U.S.

• Centimeter wavelength radar was a major contributor to the defeat of the U-boat threat.

Page 18: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 19: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 20: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 21: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 22: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

History – cont.

• After the war, the Yagi-Uda (Beam antenna) became a Ham favorite and various perturbations were developed for TV reception.

Page 23: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Part II Some Personal Notes

Objective: To provide some insights into the Japanese culture, and to show the pride the Japanese take in the fact that the Yagi-Uda was invented in their country.

Page 24: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Japan 1978

• A senior colleague and I are in Japan for an antenna conference in Sendai.

• We had a number of Japanese friends who had spent one or two years at the Antenna Laboratory at The Ohio State University when I was a graduate student 1963-1967.

• Our friends are treating us to an overnight at the Hitachi Corp. Guest House.

Page 25: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Mountains near Tokyo 1978

Page 26: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Hitachi Corp. Guest House

Page 27: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Pre Dinner Table

Page 28: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Dinner Table

Page 29: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Saying Goodbye

Page 30: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 31: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Shintaro Uda

Page 32: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 33: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 34: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 35: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Historical Recognition

• The Yagi-Uda antenna was named an IEEE Milestone in 1995.

Page 36: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Part III A Few Antenna Basics

• Wavelength

• Electromagnetic Field

• Radiation Patterns

• E-Plane and H-Plane

• Gain

Objective: To define a few basic terms used in Part IV.

Page 37: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Wavelength

0o

180o 90o

270o

360o

Page 38: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

S T U T Z M A N & T H I E L E

The Electromagnetic Field Received by an Antenna

Figure: The spatial behavior of the electric (solid) and magnetic (dashed) fields of a linearly (vertical) polarized wave for a fixed instant of time.

Ex

Hy

z

Time domian picture

E and H in time phase

The electric and magnetic fields are at right angles to each other and at right angles to the direction of propagation along the z-axis to the right.

Page 39: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 40: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

S T U T Z M A N & T H I E L E

Radiation Patterns

A radiation pattern (antenna pattern) is a graphical representation of the radiation (far-field) properties of an antenna. The radiation fields from a transmitting antenna vary inversely with distance, e.g., 1/r. The variation with observation angles (θ, ), however, depends on the antenna only. The transmit and receive patterns of an antenna are identical by reciprocity. Reciprocity allows the calculation or measurement of an antenna pattern in either the transmit or receive case, whichever is more convenient.

Page 41: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

S T U T Z M A N & T H I E L E

Pattern Characteristics

Main lobe

Minor lobes

0.5

3-D Picture

z

y

x

Major lobe (unidirectional)

Side lobe

Back lobe (in this example)

Minor lobes

Minor lobes

Half-power beamwidth (HPBW)

First null beamwidth (FNBW)

Page 42: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

S T U T Z M A N & T H I E L E

(c) Decibel pattern

Polar Radiation Patterns – cont.

(b) Relative field pattern

Page 43: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

S T U T Z M A N & T H I E L E

The concept of (maximum) gain: “how much does an antenna concentrate

radiation in one direction at the expense of other directions (if antenna ohmic

losses are included).”

Gain

1. Gain here does not include losses arising from impedance and polarization

mismatches.

2. Manufacturers usually include the impedance mismatch loss in the gain. For

a well-matched antenna, this inclusion results in the published gain being

slightly reduced.

Note:

Page 44: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 45: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Part IV A Technical Discussion

• Objective: To show the influence of the reflector and director elements, and their effect on the wave velocity.

Also, to explain how the Yagi-Uda radiates.

Page 46: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 47: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

2 Ways to understand the Yagi-Uda

• Element Phasing

• Wave approach

Page 48: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Yagi-Uda (Beam) Antennas

Page 49: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Spatial Phase Delay (Ordinary Endfire, v=c )

o o o → Forward 90o 0o -90o

⋮ λ/4 ⋮ λ/4 ⋮

Page 50: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Wave Launcher Guided Wave

Surface

Wave Launcher: Reflector and Driven Element

Guided Wave Surface: Director Elements

The Wave Approach

Page 51: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

How does a Yagi-Uda radiate?

When an electromagntic wave encounters a discontinuity, something will happen. In the case of the Yagi-Uda two things happen at the “end” of the guided wave surface: radiation and reflection. Radiation does not occur along the directors, only at the end where there is a discontinuity. That is, The Yagi-Uda is not a leaky wave antenna.

Page 52: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

27 element currents

Page 53: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Why is there usually only one reflector element?

Page 54: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

S T U T Z M A N & T H I E L E

Optimum reflector spacing SR (for maximum directivity) is between 0.15

and 0.25 wavelengths as Fig. 5-35 shows. Note that the gain above an

isolated dipole is more than 2.5 dBd, whereas if a flat plate were used,

instead of a simple wire-like element, the gain would be 3 dBd. Thus, a

single wire-like reflector element is almost as effective as a flat plate in

enhancing the gain of a dipole!

Figure 5-35 Measured

gain [21] in dBd of a

dipole and reflector

element for different

spacings SR.

Spacing SR () of reflector behind driven element

3

2

1

0.05 0.10 0.15 0.20 0.25 0.30 0.35

Reflector Driver

SR

Yagi-Uda Antenna - effect of reflector element

Page 55: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 56: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 57: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Why was a folded dipole used for the driven element in the previous

slide?

Page 58: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &
Page 59: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Answer: The mutual coupling of the driven element with the nearby parasitic elements reduces the feed point impedance, sometimes dramatically. The self impedance of a folded dipole is 4 times the self impedance of straight wire half-wave dipole, which helps to overcome the effects of mutual coupling.

Page 60: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

S T U T Z M A N & T H I E L E

Figure 5-37 Design curves for Yagi’s in Table 5-2.

Reflector

Directors

0.50

0.49

0.48

0.47

0.46

0.45

0.44

0.43

0.42

0.41

0.40

0.39

0.38 0.008 0.001 0.002 0.003 0.004 0.006 0.01 0.02 0.03

Length L Spacing SD

0.42λ Long Yagi1 Dir, 1 Refl. 0.2λ

2.2λ Long Yagi10 Dir, 1 Refl. 0.2λ

D

D

S

S

0.8λ Long Yagi3 Dir, 1 Refl, 0.2λ1.2λ Long Yagi4 Dir, 1 Refl, 0.25λ3.2λ Long Yagi15 Dir, 1 Refl, 0.2λ

4.2λ Long Yagi13 Dir, 1 Refl, 0.308λ

D

D

D

D

S

S

S

S

Diam d D1 D2 D3 . . . D4

Yagi-Uda Antennas - design

Page 61: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

S T U T Z M A N & T H I E L E

Figure 5-38 Graph

showing effect of

supporting un-insulated

metal boom on the length

of Yagi parasitic elements.

0.030

0.025

0.020

0.015

0.010

0.005

0.002 0.006 0.01 0.02 0.03 0.04

Yagi-Uda Antennas - correction for support boom

Page 62: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Question

Why can we electrically connect the metallic parasitic elements to a metallic boom?

Page 63: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

Current

Half wavelength

Voltage (-)

V (+)

Page 64: Yagi-Uda (Beam) Antenna - QCWA Barry M. Goldwater ...azqcwa.org/meetings/2016spring/yagis.pdfYagi-Uda (Beam) Antenna Gary A. Thiele KD8ZWS (Ex W8RBW) Co-author of Antenna Theory &

S T U T Z M A N & T H I E L E

TV Channel 12 Yagi Antenna Design

A 12-element Yagi for TV channel 12 at 205.25 Mhz is to be designed using

1-cm-diameter elements insulated from a metallic boom [23]. The boom length

is to be 2.2. Table 5-4 indicates that 0.2 spacing is required. The

wavelength at 205.25 Mhz is 1.46 m. Thus, the spacing between all elements is

29.2 cm. To obtain the element lengths, the following four steps are followed:

Etc, etc

0.483λ 0.4375λ1R D

L , L

Result for case “B”:

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S T U T Z M A N & T H I E L E

Figure 5-37 Design curves for Yagi’s in Table 5-2.

Reflector

Directors

0.50

0.49

0.48

0.47

0.46

0.45

0.44

0.43

0.42

0.41

0.40

0.39

0.38 0.008 0.001 0.002 0.003 0.004 0.006 0.01 0.02 0.03

Length L Spacing SD

0.42λ Long Yagi1 Dir, 1 Refl. 0.2λ

2.2λ Long Yagi10 Dir, 1 Refl. 0.2λ

D

D

S

S

0.8λ Long Yagi3 Dir, 1 Refl, 0.2λ1.2λ Long Yagi4 Dir, 1 Refl, 0.25λ3.2λ Long Yagi15 Dir, 1 Refl, 0.2λ

4.2λ Long Yagi13 Dir, 1 Refl, 0.308λ

D

D

D

D

S

S

S

S

Diam d D1 D2 D3 . . . D4

Yagi-Uda Antennas - design

B case

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S T U T Z M A N & T H I E L E

TV Channel 12 Yagi Antenna Design - cont.

x y

z z

1.0 1.0

0.75

0.5

0.25

0.75

0.5

0.25

(a) E-plane. (b) H-plane.

Figure 5-41 Calculated field patterns for Example 5-1.

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Why not use 40 or 50 director elements?

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S T U T Z M A N & T H I E L E

While it is usually not worth while to use more than one refector element,

adding director elements does increase the gain of the Yagi antenna.

However, the “law of diminishing returns” does apply as Fig. 5-36 shows.

Figure 5-36 Gain of a typical

Yagi-Uda antenna versus the

total number of elements. The

element Spacings SR = SD = 0.15. The conductor diameters

are 0.0025. (From Green [20].)

In many cases, if more than about 12 dBi of gain is desired, it is better

to consider “stacking” or arraying Yagi’s to achieve additional gain.

1

2

3

4

5

6

7

8

9

10

11

12

13

10 11 9 8 7 6 5 4 3 2 1

Yagi-Uda Antennas - effect of director elements

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An 8-Element Yagi-Uda Antenna

Illustrating the Effect of Director

Length on Pattern and Bandwidth

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Conclusion for the 8 element array

• At a director length of 0.435 wavelengths the back lobe is only down 6 dB. That is, the front to back ratio is but 6 dB, which is unacceptable.

• Further, at a director length of 0.430 wavelengths, the wave has been slowed down too much and the pattern has deteriorated . It has deteriorated even more at 0.435 wavelengths.

• The sensitivity to director length is indicative of the narrow band characteristic of the Yagi-Uda.

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Thank You !

Questions?

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The End