1. Radio Amateurs TalkRadio Amateurs Talk
Around the WorldAround the World
Without WiresWithout Wires
Yeh Right!Yeh Right!
2. All About Yagi AntennasAll About Yagi Antennas
The Yagi antenna was invented inThe Yagi antenna was invented in
Japan in 1926 by Shintaro UdaJapan in 1926 by Shintaro Uda
but published in Japanese.but published in Japanese.
The work was presented for theThe work was presented for the
first time by Professor Yagi; eitherfirst time by Professor Yagi; either
Uda's professor or colleague whoUda's professor or colleague who
went to America and gave thewent to America and gave the
first English talks on the antennafirst English talks on the antenna
Even though the antenna is oftenEven though the antenna is often
called a Yagi antenna, Udacalled a Yagi antenna, Uda
probably invented it.probably invented it.
Professor Yagi with hisProfessor Yagi with his
Yagi-Uda antennaYagi-Uda antenna
““The antenna here is a 5 elementThe antenna here is a 5 element
Uda”Uda” really doesn’t cut it!really doesn’t cut it!
3. TheThe Yagi-UdaYagi-Uda antenna orantenna or Yagi AntennaYagi Antenna
is a brilliant antenna design.is a brilliant antenna design.
A Yagi is simple to constructA Yagi is simple to construct
Yagi antennas have high gainYagi antennas have high gain
Operation from 3Mhz to 3 GhzOperation from 3Mhz to 3 Ghz
4. What aWhat a Yagi-UdaYagi-Uda Antenna Does BestAntenna Does Best
The beam from the torch partiallyThe beam from the torch partially
illuminates the totally dark areailluminates the totally dark area
We can measure and plot theWe can measure and plot the
area of radiationarea of radiation
A Yagi Concentrates it’s Beam of RadiationA Yagi Concentrates it’s Beam of Radiation
5. The Geometry of a Free Space DipoleThe Geometry of a Free Space Dipole
The same pattern applies to any centre fed dipole ½ wavelength or lessThe same pattern applies to any centre fed dipole ½ wavelength or less
• The direction of Maximum radiation is at right angles to the Axis of the dipoleThe direction of Maximum radiation is at right angles to the Axis of the dipole
• The arrows at the 45 degree and 315 degree points are the half power or -3 Db pointsThe arrows at the 45 degree and 315 degree points are the half power or -3 Db points
6.
7.
8.
9. A 2 ElementA 2 Element YagiYagi Shown In Two ConfigurationsShown In Two Configurations
Both are almost equal in Gain and DirectionBoth are almost equal in Gain and Direction
The Director is about 5% Shorter thanThe Director is about 5% Shorter than
the DE (Driven Element)the DE (Driven Element)
The Reflector is about 5% LongererThe Reflector is about 5% Longerer
than the DE (Driven Element)than the DE (Driven Element)
Two-element Yagi systems using a single parasitic element. At A theTwo-element Yagi systems using a single parasitic element. At A the
parasitic element acts as a director, and at B as a reflector. The arrowsparasitic element acts as a director, and at B as a reflector. The arrows
show the direction in which maximum radiation takes place.show the direction in which maximum radiation takes place.
10. Let’s Add a ReflectorLet’s Add a Reflector
The reflector is the element that is placed at the rear of the driven element (TheThe reflector is the element that is placed at the rear of the driven element (The
dipole). It's resonant frequency is lower, and its length is approximately 5% longerdipole). It's resonant frequency is lower, and its length is approximately 5% longer
than the driven element. It's length will vary depending on the spacing and thethan the driven element. It's length will vary depending on the spacing and the
element diameter.element diameter.
The spacing of the reflector will be between 0.1 wavelength and 0.25 wavelength.The spacing of the reflector will be between 0.1 wavelength and 0.25 wavelength.
It's spacing will depend upon the gain, bandwidth, F/B ratio, and sidelobe patternIt's spacing will depend upon the gain, bandwidth, F/B ratio, and sidelobe pattern
requirements of the final antenna design.requirements of the final antenna design.
11.
12. Let’s Add a DirectorLet’s Add a Director
The director is the shortest of the parasitic elements and this end of the Yagi isThe director is the shortest of the parasitic elements and this end of the Yagi is
aimed at the receiving station. It is resonant slightly higher in frequency than theaimed at the receiving station. It is resonant slightly higher in frequency than the
driven element, and its length will be about 5% shorter, progressively than thedriven element, and its length will be about 5% shorter, progressively than the
driven element.driven element.
The director/s are used to provide the antenna with directional pattern and gain.The director/s are used to provide the antenna with directional pattern and gain.
The amount of gain is directly proportional to the length of the antenna array and notThe amount of gain is directly proportional to the length of the antenna array and not
by the number of directors used. The spacing of the directors can range from 0.1by the number of directors used. The spacing of the directors can range from 0.1
wavelength to 0.5 wavelength or more and will depend largely upon the designwavelength to 0.5 wavelength or more and will depend largely upon the design
specifications of the antennaspecifications of the antenna..
13.
14.
15. • Many hams consider a 2-element Yagi to give “the mostMany hams consider a 2-element Yagi to give “the most
bang for the buck” among various Yagi designs,bang for the buck” among various Yagi designs,
particularly for portable operations.particularly for portable operations.
WHY?WHY?
• A 2-element Yagi has about 4 dB of gain over a simpleA 2-element Yagi has about 4 dB of gain over a simple
dipole (sometimes jokingly called a “one-element Yagi”)dipole (sometimes jokingly called a “one-element Yagi”)
and gives a modest F/B ratio of about 10 dB to help withand gives a modest F/B ratio of about 10 dB to help with
rejection of interference on receive.rejection of interference on receive.
• By comparison, going from a 2-element to a 3-elementBy comparison, going from a 2-element to a 3-element
Yagi increases the boom length by about 50% and addsYagi increases the boom length by about 50% and adds
another element, a 50% increase in the number ofanother element, a 50% increase in the number of
elements—for a gain increase of about 1 dB and anotherelements—for a gain increase of about 1 dB and another
10 dB in F/B ratio.10 dB in F/B ratio.
OPTIMUM DESIGNS AND ELEMENT SPACINGOPTIMUM DESIGNS AND ELEMENT SPACING
Two-Element YagisTwo-Element Yagis
16. The Yagi -Uda Antenna BasicsThe Yagi -Uda Antenna Basics
• Driven element is excited directly via feedline, all otherDriven element is excited directly via feedline, all other
elements excited parasiticallyelements excited parasitically
• Lengths and diameters of elements, plus their spacingLengths and diameters of elements, plus their spacing
determine antenna behavior.determine antenna behavior.
• Driven element size and diameter has little effect onDriven element size and diameter has little effect on
forward gain, but significant in, effect on input impedanceforward gain, but significant in, effect on input impedance
and backward gain.and backward gain.
• Reflector spacing and size has little effect on forwardReflector spacing and size has little effect on forward
gain, but significant effect on backward gain as well as inputgain, but significant effect on backward gain as well as input
impedance.impedance.
• Directors, the most critical part of a Yagi design, controlDirectors, the most critical part of a Yagi design, control
front and backward gain, and input impedance.front and backward gain, and input impedance.
17. How Does A Yagi Generate “Gain” ?How Does A Yagi Generate “Gain” ?
• Signals arriving at A strikes all three elements and generates a current on each element.Signals arriving at A strikes all three elements and generates a current on each element.
The signals are re-radiated by the director and reflector and arrive at the driven elementThe signals are re-radiated by the director and reflector and arrive at the driven element in-in-
phasephase with one another (the two re-radiated signals and the original signal). The signalswith one another (the two re-radiated signals and the original signal). The signals
reinforce each other...and make the incoming signal much stronger coming from direction Areinforce each other...and make the incoming signal much stronger coming from direction A
• When the signal comes from direction B and C except that they arrive at the drivenWhen the signal comes from direction B and C except that they arrive at the driven
elementelement out-of-phaseout-of-phase with one another which simply means they cancel each other out,with one another which simply means they cancel each other out,
significantly reducing signals from direction B and C.significantly reducing signals from direction B and C.
18. More Elements = Greater GainMore Elements = Greater Gain
As you add more elements you enter the harsh worldAs you add more elements you enter the harsh world
of diminishing gain for additional added elementsof diminishing gain for additional added elements
19. • The Chart gain figures are approximate dbi.The Chart gain figures are approximate dbi.
• Subtract about 2 db for the real world of db gain.Subtract about 2 db for the real world of db gain.
• Note the harsh world of diminishing gain for more added elementsNote the harsh world of diminishing gain for more added elements
20. • Here is an Azimuth (Looking from above)Here is an Azimuth (Looking from above)
pattern for 6-element 20-meter Yagi on 60-pattern for 6-element 20-meter Yagi on 60-
foot long boom, mounted 60 feet overfoot long boom, mounted 60 feet over
ground.ground.
• AtAt AA, the azimuth pattern angle is shown, the azimuth pattern angle is shown
compared to a dipole at the same height.compared to a dipole at the same height.
Peak gain of the Yagi is 16.04 dBi, or justPeak gain of the Yagi is 16.04 dBi, or just
over 8 dB compared to the dipole.over 8 dB compared to the dipole.
• AtAt BB, the elevation pattern for the same two, the elevation pattern for the same two
antennas is shown. Note that the peakantennas is shown. Note that the peak
elevation pattern of the Yagi is compressedelevation pattern of the Yagi is compressed
slightly lower compared to the dipole, evenslightly lower compared to the dipole, even
though they are both at the same height overthough they are both at the same height over
ground.ground.
Multi – Element Yagis = Gain and PowerMulti – Element Yagis = Gain and Power
21. A Typical 80m/40mTrap DipoleA Typical 80m/40mTrap Dipole
An 80m / 40m trap dipole for operation with 75-Ω feederAn 80m / 40m trap dipole for operation with 75-Ω feeder
at low SWR (C. L. Buchanan, W3DZZ). The balancedat low SWR (C. L. Buchanan, W3DZZ). The balanced
(parallel-conductor) line indicated is desirable, but 75-Ω(parallel-conductor) line indicated is desirable, but 75-Ω
coax can be substituted with some sacrifice of symmetrycoax can be substituted with some sacrifice of symmetry
in the system. A Balun may also be used but is usuallyin the system. A Balun may also be used but is usually
not necessary.not necessary.
Dimensions given are for resonance (lowest SWR) atDimensions given are for resonance (lowest SWR) at
3.75 and 7.2 with SWR less than 2:1 throughout the3.75 and 7.2 with SWR less than 2:1 throughout the
band.band.
7 Mhz
40M Trap
7 Mhz
40M Trap
22. Trap Antenna Current & Voltage DistributionTrap Antenna Current & Voltage Distribution
50 or 75
Ohm
Coax
Cable
7 Mhz
40M
Trap
Current
Half Wave on
40M
Voltage
80M – 40M
Current
Half Wave on
80M
7 Mhz
40M
Trap
40m Operation
Feed the antenna with 40m energy and
the 40m traps prevent current flow into
the 80m portion of the antenna. The
antenna now looks like a half wave on
80M
80m Operation
Feed the antenna with 80m energy and
the 40m traps allow current flow into the
80m portion of the antenna. The antenna
now looks like a half wave on 80M. The
small trap inductance actually shortens
the length of the antenna
• A Typical 80m/40mTrap Dipole. The 40m portion length of wire is 66’ – the normal
half wave length.
• The full 80m portion is approximately 105’ – slightly shorter than the normal length
of 130’
( Wire Dipole )( Wire Dipole )
23. How Are Traps Constructed?How Are Traps Constructed?
A close-up view of the original W3DZZ trap.A close-up view of the original W3DZZ trap.
The coil is 3 inches in diameter. The leadsThe coil is 3 inches in diameter. The leads
from the coaxial-cable capacitor should befrom the coaxial-cable capacitor should be
soldered directly to the pigtails of the coil.soldered directly to the pigtails of the coil.
These connections should be coated withThese connections should be coated with
varnish after they have been secured undervarnish after they have been secured under
the hose clamps.the hose clamps.
This home made Trap uses a plastic rod betweenThis home made Trap uses a plastic rod between
the two alloy tabes with an inductance coil inthe two alloy tabes with an inductance coil in
parallel with a “Coax” capacitor to form a trap inparallel with a “Coax” capacitor to form a trap in
the element. The RG8 coax has 25 Pfthe element. The RG8 coax has 25 Pf
capacitance each 25mm of length and is used ascapacitance each 25mm of length and is used as
the capacitor. The other end of the coax is openthe capacitor. The other end of the coax is open
This home made Trap uses coaxial cable woundThis home made Trap uses coaxial cable wound
over a short piece of PVC tubing to form a trapover a short piece of PVC tubing to form a trap
in the element. The coax represents thein the element. The coax represents the
inductance AND the capacitance and allows theinductance AND the capacitance and allows the
trap to resonate as the traditional parallel tunedtrap to resonate as the traditional parallel tuned
circuitcircuit
24. Multiband Yagis using a single boom can also be madeMultiband Yagis using a single boom can also be made
using traps. Traps allow an element to have multipleusing traps. Traps allow an element to have multiple
resonances.resonances.
Commercial vendors such as Hy-Gain, Mosley, TET,Commercial vendors such as Hy-Gain, Mosley, TET,
Nagoya, Cushcraft, Telex, Wilson and others have soldNagoya, Cushcraft, Telex, Wilson and others have sold
trapped antennas to hams since the 1950s and surveystrapped antennas to hams since the 1950s and surveys
show that after simple wire dipoles and multibandshow that after simple wire dipoles and multiband
verticals, trapped triband Yagis are the most popularverticals, trapped triband Yagis are the most popular
antennas in the Amateur Radio service.antennas in the Amateur Radio service.
The trapped tribander was invented by ChesterThe trapped tribander was invented by Chester
Buchanan, W3DZZ, and described in his March 1955Buchanan, W3DZZ, and described in his March 1955
QSTQST articlearticle
Yagis – Trapped MultibandersYagis – Trapped Multibanders
25. Trap Antenna Current & Voltage DistributionTrap Antenna Current & Voltage Distribution
Feed point
Usually coaxial
cable
Half Wave on
20M
10M
20m Operation
The 20m energy passes through the 10m and
15m traps and allows the element to operate on
20M as if the traps were not there.
The small trap inductance actually shortens the
length of the antenna (28’ vs full size 33’)
Half Wave on
15M
Half Wave on
10M
10M15M 15M
15m Operation
The 10m energy stops at the 10m trap. The 10m
portion of the element is full size on 10M and
operates as a normal half wave dipole element.
The 15m energy passes through the 10m trap
and is stopped by the 15m trap.
The 10m trap allows the element to operate on
15M as if the 10m trap was not there.
( Triband Yagi )( Triband Yagi )
Tribander DRIVEN ELEMENT
26. Sleeve Driven Element Multiband AntennasSleeve Driven Element Multiband Antennas
• The basic two-element quad antenna, with driven-element loop and reflector loop. TheThe basic two-element quad antenna, with driven-element loop and reflector loop. The
driven loops are electrically one wavelength in circumference (1/4 wavelength on adriven loops are electrically one wavelength in circumference (1/4 wavelength on a
side); the reflectors are slightly longer. Both configurations shown give horizontalside); the reflectors are slightly longer. Both configurations shown give horizontal
polarization.polarization.
The Force 12 Commercial Tribander AntennaThe Force 12 Commercial Tribander Antenna
20M DE20M REF
10M Passive DE
15M REF
10M REF
15M Passive DE
27. The Variable Element SteppIR AntennasThe Variable Element SteppIR Antennas
• This antenna has motor driven adjustable length elements controlled by a controller inThis antenna has motor driven adjustable length elements controlled by a controller in
the shack which is controlled by the transceiver. The SteppIR has the ability to adjustthe shack which is controlled by the transceiver. The SteppIR has the ability to adjust
the length of the elements for each different band. It also will interchange the lengths ofthe length of the elements for each different band. It also will interchange the lengths of
the Director and reflector within a few seconds so that the beam reverses direction bythe Director and reflector within a few seconds so that the beam reverses direction by
180 degrees.180 degrees.
28. Spiderbeam Multiband AntennasSpiderbeam Multiband Antennas
The basic antenna principle is quite simple. No magic involved. Start with a normal 3 element yagiThe basic antenna principle is quite simple. No magic involved. Start with a normal 3 element yagi
and bend the director and reflector in a V-Shape. The resulting antenna can be built using wireand bend the director and reflector in a V-Shape. The resulting antenna can be built using wire
elements strung on a supporting cross, which makes it possible to use lightweight materials likeelements strung on a supporting cross, which makes it possible to use lightweight materials like
fiberglass and wire. Bending the element ends towards each other has the additional benefit offiberglass and wire. Bending the element ends towards each other has the additional benefit of
enhanced coupling between the elements ("capacitive/inductive end coupling"), which in turnenhanced coupling between the elements ("capacitive/inductive end coupling"), which in turn
seems to enhance the F/B ratio and antenna operating bandwidth.seems to enhance the F/B ratio and antenna operating bandwidth.
29. HexBeam Multiband AntennasHexBeam Multiband Antennas
The hexagonal beam offers a number of features as follows:The hexagonal beam offers a number of features as follows:
Gain and front/back comparable to a two element yagi.Gain and front/back comparable to a two element yagi.
Five bands with low SWRFive bands with low SWR
Broad band characteristicsBroad band characteristics
Low weight and low wind loadLow weight and low wind load
Construction from general hardware componentsConstruction from general hardware components
Ease of adjustmentEase of adjustment
30. Quads and Quad Multiband AntennasQuads and Quad Multiband Antennas
• The basic two-element quad antenna, with driven-element loop and reflector loop. TheThe basic two-element quad antenna, with driven-element loop and reflector loop. The
driven loops are electrically one wavelength in circumference (1/4 wavelength on adriven loops are electrically one wavelength in circumference (1/4 wavelength on a
side); the reflectors are slightly longer. Both configurations shown give horizontalside); the reflectors are slightly longer. Both configurations shown give horizontal
polarization.polarization.
• For vertical polarization, the driven element should be fed at one of the side corners inFor vertical polarization, the driven element should be fed at one of the side corners in
the arrangement at the left, or at the center of a vertical side in the “square” quad at thethe arrangement at the left, or at the center of a vertical side in the “square” quad at the
right.right.
31. • Yagis are One trick ponies and will operate on One band onlyYagis are One trick ponies and will operate on One band only
• A Yagi antenna can be turned into a Multi-band antennaA Yagi antenna can be turned into a Multi-band antenna
• Multi-band Yagis are compromise antennasMulti-band Yagis are compromise antennas
• We can use resonant traps, Sleeve coupling, LoadedWe can use resonant traps, Sleeve coupling, Loaded
elements and other methods to gain more bands.elements and other methods to gain more bands.
• The cost is that we usually lose some gain, F/B ratio and/orThe cost is that we usually lose some gain, F/B ratio and/or
directivity at the expense of multi-band versatilitydirectivity at the expense of multi-band versatility
•The reality is that most of these 2, 3 and 4el yagi and trapThe reality is that most of these 2, 3 and 4el yagi and trap
antennas work very well and perform infinitely better than aantennas work very well and perform infinitely better than a
vertical or wire antenna.vertical or wire antenna.
Yagi Antenna SummaryYagi Antenna Summary
