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Yagi Antennas Presentation

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Yagi Antennas Presentation

  1. 1. Radio Amateurs TalkRadio Amateurs Talk Around the WorldAround the World Without WiresWithout Wires Yeh Right!Yeh Right!
  2. 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. 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. 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. 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. 6. 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.
  7. 7. 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.
  8. 8. 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..
  9. 9. • 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
  10. 10. 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.
  11. 11. 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.
  12. 12. 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
  13. 13. • 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
  14. 14. • 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
  15. 15. 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
  16. 16. 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 )
  17. 17. 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
  18. 18. 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
  19. 19. 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
  20. 20. 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
  21. 21. 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.
  22. 22. 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.
  23. 23. 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
  24. 24. 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.
  25. 25. • 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
  26. 26. The EndThe End A ZL2AL ResourceA ZL2AL Resource

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