Radio Amateurs Talk Radio Amateurs Talk Around the World Around the World

Without WiresWithout Wires

Yeh Right!Yeh Right!

All About Yagi AntennasAll About Yagi AntennasThe Yagi antenna was invented in The Yagi antenna was invented in Japan in 1926 by Shintaro Uda Japan in 1926 by Shintaro Uda but published in Japanese. but published in Japanese.

The work was presented for the The work was presented for the first time by Professor Yagi; either first time by Professor Yagi; either Uda's professor or colleague who Uda's professor or colleague who went to America and gave the went to America and gave the first English talks on the antenna first English talks on the antenna

Even though the antenna is often Even though the antenna is often called a Yagi antenna, Uda called a Yagi antenna, Uda probably invented it. probably invented it.

Professor Yagi with his Professor 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!

The The Yagi-UdaYagi-Uda antenna or antenna 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

What a What a Yagi-UdaYagi-Uda Antenna Does Best Antenna Does Best

The beam from the torch partially The beam from the torch partially illuminates the totally dark areailluminates the totally dark area

We can measure and plot the We 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

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

A 2 Element A 2 Element Yagi Yagi 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 than The Director is about 5% Shorter than the DE (Driven Element)the DE (Driven Element)

The Reflector is about 5% Longerer The 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 the Two-element Yagi systems using a single parasitic element. At A the parasitic element acts as a director, and at B as a reflector. The arrows parasitic 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.

Let’s Add a ReflectorLet’s Add a ReflectorThe reflector is the element that is placed at the rear of the driven element (The The 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% longer dipole). 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 the than 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 pattern It'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.

Let’s Add a DirectorLet’s Add a DirectorThe director is the shortest of the parasitic elements and this end of the Yagi is The 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 the aimed 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 the driven 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 not The 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 0.1 by 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 design wavelength to 0.5 wavelength or more and will depend largely upon the design specifications of the antennaspecifications of the antenna..

• Many hams consider a 2-element Yagi to give “the most Many 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 simple A 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 with and 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-element By comparison, going from a 2-element to a 3-element Yagi increases the boom length by about 50% and adds Yagi increases the boom length by about 50% and adds another element, a 50% increase in the number of another element, a 50% increase in the number of elements—for a gain increase of about 1 dB and another elements—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 SPACINGTwo-Element YagisTwo-Element Yagis

The Yagi -Uda Antenna BasicsThe Yagi -Uda Antenna Basics• Driven element is excited directly via feedline, all other Driven element is excited directly via feedline, all other elements excited parasitically elements excited parasitically

• Lengths and diameters of elements, plus their spacing Lengths and diameters of elements, plus their spacing determine antenna behavior.determine antenna behavior.

• Driven element size and diameter has little effect on Driven element size and diameter has little effect on forward gain, but significant in, effect on input impedance forward gain, but significant in, effect on input impedance and backward gain.and backward gain.

• Reflector spacing and size has little effect on forward Reflector spacing and size has little effect on forward gain, but significant effect on backward gain as well as input gain, but significant effect on backward gain as well as input impedance.impedance.

• Directors, the most critical part of a Yagi design, control Directors, the most critical part of a Yagi design, control front and backward gain, and input impedance.front and backward gain, and input impedance.

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 element The signals are re-radiated by the director and reflector and arrive at the driven element in-in-phase phase with one another (the two re-radiated signals and the original signal). The signals with 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 driven When the signal comes from direction B and C except that they arrive at the driven element element out-of-phase out-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.

More Elements = Greater GainMore Elements = Greater Gain

As you add more elements you enter the harsh world As you add more elements you enter the harsh world of diminishing gain for additional added elementsof diminishing gain for additional added elements

• 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

• 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 over foot long boom, mounted 60 feet over ground.ground. • At At 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 just Peak gain of the Yagi is 16.04 dBi, or just over 8 dB compared to the dipole. over 8 dB compared to the dipole.

• At At BB, the elevation pattern for the same two , the elevation pattern for the same two antennas is shown. Note that the peak antennas is shown. Note that the peak elevation pattern of the Yagi is compressed elevation pattern of the Yagi is compressed slightly lower compared to the dipole, even slightly lower compared to the dipole, even though they are both at the same height over though they are both at the same height over ground. ground.

Multi – Element Yagis = Gain and PowerMulti – Element Yagis = Gain and Power

A Typical 80m/40mTrap DipoleA Typical 80m/40mTrap Dipole

An 80m / 40m trap dipole for operation with 75-Ω feeder An 80m / 40m trap dipole for operation with 75-Ω feeder at low SWR (C. L. Buchanan, W3DZZ). The balanced at 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 symmetry coax can be substituted with some sacrifice of symmetry in the system. A Balun may also be used but is usually in the system. A Balun may also be used but is usually not necessary.not necessary.

Dimensions given are for resonance (lowest SWR) at Dimensions given are for resonance (lowest SWR) at 3.75 and 7.2 with SWR less than 2:1 throughout the 3.75 and 7.2 with SWR less than 2:1 throughout the band.band.

7 Mhz

40M Trap

7 Mhz

40M Trap

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 )

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 leads The coil is 3 inches in diameter. The leads from the coaxial-cable capacitor should be from the coaxial-cable capacitor should be soldered direct ly to the pigtai ls of the coil . soldered direct ly to the pigtai ls of the coil . These connect ions should be coated with These connect ions should be coated with varnish after they have been secured under varnish after they have been secured under the hose clamps.the hose clamps.

This home made Trap uses a plast ic rod between This home made Trap uses a plast ic rod between the two alloy tabes with an inductance coil in the two alloy tabes with an inductance coil in parallel with a “Coax” capacitor to form a trap in parallel with a “Coax” capacitor to form a trap in the element. The RG8 coax has 25 Pf the element. The RG8 coax has 25 Pf capacitance each 25mm of length and is used as capacitance 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 wound This home made Trap uses coaxial cable wound over a short piece of PVC tubing to form a trap over a short piece of PVC tubing to form a trap in the element. The coax represents the in the element. The coax represents the inductance AND the capacitance and allows the inductance AND the capacitance and allows the trap to resonate as the tradit ional parallel tuned trap to resonate as the tradit ional parallel tuned circuitcircuit

Multiband Yagis using a single boom can also be made Multiband Yagis using a single boom can also be made using traps. Traps allow an element to have multiple using 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 sold Nagoya, Cushcraft, Telex, Wilson and others have sold trapped antennas to hams since the 1950s and surveys trapped antennas to hams since the 1950s and surveys show that after simple wire dipoles and multiband show that after simple wire dipoles and multiband verticals, trapped triband Yagis are the most popular verticals, 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 Chester The trapped tribander was invented by Chester Buchanan, W3DZZ, and described in his March 1955 Buchanan, W3DZZ, and described in his March 1955 QST QST article article

Yagis – Trapped MultibandersYagis – Trapped Multibanders

Trap Antenna Current & Voltage DistributionTrap Antenna Current & Voltage Distribution

Feed pointUsually coaxial

cable

Half Wave on 20M

10M

20m OperationThe 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 OperationThe 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

Sleeve Driven Element Multiband AntennasSleeve Driven Element Multiband Antennas

• The basic two-element quad antenna, with driven-element loop and reflector loop. The The 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 a driven loops are electrically one wavelength in circumference (1/4 wavelength on a side); the reflectors are slightly longer. Both configurations shown give horizontal side); 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

The Variable Element SteppIR AntennasThe Variable Element SteppIR Antennas

• This antenna has motor driven adjustable length elements controlled by a controller in This 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 adjust the 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 of the 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 by the Director and reflector within a few seconds so that the beam reverses direction by 180 degrees.180 degrees.

Spiderbeam Multiband AntennasSpiderbeam Multiband Antennas

The basic antenna principle is quite simple. No magic involved. Start with a normal 3 element yagi The 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 wire and 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 like elements 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 of fiberglass 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 turn enhanced 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.

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

Quads and Quad Multiband AntennasQuads and Quad Multiband Antennas

• The basic two-element quad antenna, with driven-element loop and reflector loop. The The 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 a driven loops are electrically one wavelength in circumference (1/4 wavelength on a side); the reflectors are slightly longer. Both configurations shown give horizontal side); 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 in For 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 the the arrangement at the left, or at the center of a vertical side in the “square” quad at the right.right.

• 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, Loaded We 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/or The 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 trap The reality is that most of these 2, 3 and 4el yagi and trap antennas work very well and perform infinitely better than a antennas work very well and perform infinitely better than a vertical or wire antenna. vertical or wire antenna.

Yagi Antenna SummaryYagi Antenna Summary

The EndThe End

A ZL2AL ResourceA ZL2AL Resource