Ham Radio Yagi Antennas — Complete Guide
The Yagi-Uda antenna is the most widely used directional antenna in amateur radio — and for good reason. A 3-element Yagi delivers approximately 7 dBd of gain, equivalent to multiplying your transmitter power by five in the forward direction. Used on HF for DX and contesting, on VHF and UHF for weak-signal work and satellite operation, and at microwave frequencies for EME, the Yagi is the fundamental high-performance antenna design across all amateur frequency ranges.
HF 3-Element Yagi
The classic HF beam — one reflector, driven element, and one director on an aluminum boom. ~7 dBd gain, ~20 dB F/B ratio. The most common rotatable HF antenna for 10m through 20m at typical tower heights of 30–60 feet.
Multi-Band Yagi (Trap / Interlaced)
A Yagi covering multiple HF bands from a single boom using trap elements or interlaced element sets. Covers 10/15/20m from one antenna — the dominant commercial HF beam design. Slightly reduced performance per band compared to a dedicated single-band Yagi.
VHF Yagi — 2m and 6m
At VHF frequencies, Yagis can have many elements on a manageable boom length. A 5-element 2m Yagi fits on a 6-foot boom and delivers ~10 dBd. Used for weak-signal SSB, satellite work, EME first steps, and meteor scatter.
UHF Yagi — 70cm and Above
At 70cm and higher frequencies, high-gain Yagis are physically compact. A 9-element 70cm Yagi fits on a 3-foot boom delivering ~13 dBd. Precision construction is important — dimensional tolerances become more critical as frequency increases.
Cross-Yagi — Satellite & EME
Two Yagis mounted at 90° on the same boom, fed with a phasing harness for circular polarization. Essential for LEO satellite operation to combat spin fading, and for EME where polarization rotation from the ionosphere and Faraday rotation cause continuous polarity change.
OWA Yagi
The Optimum Wideband Antenna design by N6LF and KL7UW. Uses a specific director spacing pattern to achieve very low SWR across an entire amateur band without a matching network — particularly valuable for 20m and 40m where the band is wide.
Log-Yagi (LY)
A hybrid design combining a log-periodic driven array with additional Yagi directors forward of the LPDA. Delivers higher gain than a pure log-periodic with broader bandwidth than a pure Yagi — a popular choice for HF contest stations wanting one antenna to cover multiple bands.
Moxon Rectangle
A 2-element Yagi variant with folded-back tips forming a rectangular shape. Approximately 30% smaller footprint than a full-size Yagi with comparable gain (~5 dBd) and excellent front-to-back ratio. Wire construction on a PVC frame — no metal fabrication needed.
Parasitic Element Operation
A Yagi-Uda antenna uses parasitic elements — conductors that are not connected to the feedline but interact electromagnetically with the driven element. When an RF wave from the driven element reaches a parasitic element, it induces a current in that element. The parasitic element then re-radiates, and the phase and amplitude of this re-radiated signal either adds to or subtracts from the driven element's radiation depending on the element's length and spacing.
The two parasitic element types behave differently:
- Reflector — slightly longer than the driven element (typically ~5% longer). Positioned behind the driven element. Re-radiates with a phase that reinforces forward radiation and cancels rearward radiation
- Director — slightly shorter than the driven element (typically ~4–5% shorter). Positioned in front of the driven element. Re-radiates in phase with forward radiation, adding constructively to the forward lobe
- Adding more directors increases forward gain — each additional director adds approximately 1 dBd of gain with diminishing returns beyond about 6–8 elements
- The reflector contributes primarily to F/B ratio — one reflector is usually sufficient regardless of how many directors are used
Gain, F/B Ratio, and Trade-offs
Every Yagi design involves trade-offs between gain, front-to-back ratio, bandwidth, and feedpoint impedance. These four parameters cannot all be simultaneously maximized — optimizing for one degrades others.
- Maximum gain design: highest forward gain but narrow bandwidth and often poor F/B ratio and low feedpoint impedance requiring a matching network
- Maximum F/B design: best rejection of signals from behind but reduced forward gain and narrow operating bandwidth
- OWA design: sacrifices some peak gain for wide bandwidth and 50Ω feedpoint — the most practical for amateur bands that span several percent of center frequency
- Balanced design (NBS): reasonable gain, reasonable F/B, reasonable bandwidth, and a feedpoint impedance near 50Ω — the starting point for most homebrew 3-element Yagis
Element Dimensions and Spacing
Yagi element lengths and spacings are expressed as fractions of a wavelength. This makes the design scalable to any frequency — multiply by the wavelength at the operating frequency to get physical dimensions. The NBS (National Bureau of Standards) optimized 3-element design is a widely used starting point:
These ratios apply regardless of frequency. For 14.200 MHz (20m) where λ = 69.3 ft: the reflector is 35.0 ft, driven element 32.8 ft, director 30.5 ft, total boom 38.1 ft. For 144.200 MHz (2m) where λ = 6.82 ft: reflector 3.44 ft, driven 3.23 ft, director 3.00 ft, boom 3.75 ft.
Yagi element calculator →Element Diameter and Boom Correction
Element diameter significantly affects the optimum element length. Thicker elements (larger diameter relative to wavelength) resonate at a slightly shorter length than the NBS thin-element ratios predict. This requires a correction to the published dimensions:
- For HF Yagis using 3/8" to 3/4" tubing elements: reduce all element lengths by 1–3% from the thin-wire calculation
- For VHF Yagis using 1/4" to 3/8" rod or tubing: element diameter correction is smaller but still measurable
- Use NEC2 modeling with actual element diameter to determine precise dimensions before cutting
Boom correction is equally important when elements are mounted through a conductive boom. The boom's influence on the element's electrical length must be compensated for — typically by lengthening elements that pass through the boom by a correction factor based on the boom diameter. Elements mounted on insulated standoffs above the boom are unaffected.
- Element through 3/4" boom: add approximately 0.75" to element length at VHF
- Element through 1.5" boom: add approximately 1.25" at VHF
- At HF, boom correction is smaller relative to element length but still should be applied for precision designs
- The YO software automatically calculates boom corrections for the specified boom diameter
| Band | Frequency | Reflector | Driven Element | Director | Refl–Driven | Driven–Dir | Total Boom | Est. Gain |
|---|---|---|---|---|---|---|---|---|
| 20m | 14.200 MHz | 34.97 ft | 32.78 ft | 30.50 ft | 13.87 ft | 24.27 ft | 38.14 ft | ~7 dBd |
| 17m | 18.120 MHz | 27.40 ft | 25.67 ft | 23.88 ft | 10.87 ft | 19.01 ft | 29.88 ft | ~7 dBd |
| 15m | 21.200 MHz | 23.43 ft | 21.95 ft | 20.42 ft | 9.29 ft | 16.26 ft | 25.55 ft | ~7 dBd |
| 12m | 24.940 MHz | 19.92 ft | 18.66 ft | 17.36 ft | 7.90 ft | 13.82 ft | 21.72 ft | ~7 dBd |
| 10m | 28.500 MHz | 17.43 ft | 16.33 ft | 15.19 ft | 6.91 ft | 12.09 ft | 19.00 ft | ~7 dBd |
| 6m | 50.100 MHz | 9.93 ft | 9.30 ft | 8.65 ft | 3.93 ft | 6.89 ft | 10.82 ft | ~7 dBd |
| 2m | 144.200 MHz | 41.5 in | 38.9 in | 36.2 in | 16.4 in | 28.7 in | 45.1 in | ~7 dBd |
| 1.25m | 222.100 MHz | 27.0 in | 25.3 in | 23.5 in | 10.7 in | 18.6 in | 29.3 in | ~7 dBd |
| 70cm | 432.100 MHz | 13.8 in | 13.0 in | 12.1 in | 5.5 in | 9.6 in | 15.0 in | ~7 dBd |
Dimensions based on NBS optimized 3-element ratios (reflector 0.505λ, driven 0.473λ, director 0.440λ, spacings 0.200λ and 0.350λ). Apply element diameter and boom corrections before cutting. Use the Yagi calculator for frequency-specific dimensions.
Why Yagi Driven Elements Need Matching
The driven element of a Yagi in the presence of parasitic elements does not present the same 73Ω impedance as an isolated half-wave dipole. The mutual coupling between the driven element and the reflector/directors modifies the feedpoint impedance — for most 3-element Yagi designs, the impedance at the driven element feedpoint is approximately 20–30Ω, not 50Ω.
Several matching methods are used to transform this impedance to 50Ω:
- Gamma match — an adjustable tapping arrangement using a short parallel conductor and series capacitor. Allows fine-tuning after installation. The most common commercial and homebrew match for HF Yagis.
- T-match — similar to the gamma match but symmetric, feeding both sides of the driven element. Often used with a balun to maintain balance.
- Beta (hairpin) match — a short inductive stub across the driven element feedpoint that resonates with the capacitive reactance of a slightly shortened driven element, transforming the impedance to 50Ω. Simple and reliable.
- Direct 50Ω feed — possible with OWA designs that specifically optimize element dimensions and spacing to produce a 50Ω feedpoint directly, eliminating the need for any matching network.
Gamma Match Construction and Adjustment
The gamma match is the most common feed system for homebrew HF Yagis. It consists of a short aluminum rod running parallel to and connected at one end to the center of the driven element, with a series capacitor (typically 50–200 pF variable) connecting the rod to the coax center conductor. The braid connects directly to the driven element center.
Gamma match adjustment procedure:
- Start with the gamma rod approximately 0.04–0.05λ long and set the capacitor to mid-range
- Connect the NanoVNA and sweep through the band — observe the impedance on the Smith chart
- Adjust the gamma rod length to move the resistive component toward 50Ω
- Adjust the capacitor to cancel residual reactance
- Iterate between rod length and capacitor until 50Ω is achieved — this typically takes 3–5 iterations
- Once optimized, replace the variable capacitor with a fixed value or use a sealed variable capacitor for weatherproofing
Baluns on Yagi Antennas
A Yagi driven element is a balanced structure — a half-wave dipole. Coaxial cable is unbalanced. Without a balun, common-mode current flows on the outside of the coax, distorting the Yagi's radiation pattern and affecting front-to-back performance. The impact is more noticeable on a Yagi than on a simple dipole because the Yagi's performance depends on precise current distributions across multiple elements.
- A current choke (1:1 current balun) at the driven element feedpoint is strongly recommended for all Yagi installations
- For HF Yagis, wind 8–10 turns of coax through an FT-240-31 toroid immediately behind the driven element feedpoint
- The coax then runs along the boom toward the mast — secure every 2 feet to prevent the coax from becoming an unintentional parasitic element
- At VHF and UHF, a sleeve balun (choke balun formed by the coax and a quarter-wave sleeve of outer conductor) is common
- Common-mode current on the coax running along the boom is a frequent source of pattern distortion in commercial HF Yagis — many operators add a current choke after purchase
Boom-to-Mast Connection and Rotation
A rotatable HF Yagi on a tower requires a mast and rotator capable of supporting the antenna's wind load and weight. Key mechanical considerations:
- Calculate wind survival load — a 20m 3-element Yagi has a wind area of approximately 8–12 sq ft; verify the rotator's torque rating exceeds the wind moment at your design wind speed
- The boom-to-mast plate must be centered at the antenna's mechanical balance point — typically near but not exactly at the driven element position
- Use a thrust bearing above the rotator to carry the downward weight of the antenna and prevent it from loading the rotator shaft in thrust
- Wrap coax in a loop at the mast top before running it down — this service loop allows mast rotation without stressing the coax connector
- Use UV-resistant cable ties to secure the coax to the boom every 18–24 inches
- Aluminum boom-to-element clamps should use stainless hardware and Noalox on all aluminum-to-aluminum contact surfaces to prevent galvanic corrosion and seizing
Trap Yagis
A trap Yagi uses resonant LC traps along each element to create multiple resonant lengths from a single physical element. On the highest covered band, the traps act as open circuits and only the inner section of each element radiates. On lower bands, the traps' impedance is low and the full element length is active.
The most common commercial HF beam design — the classic tri-band Yagi covering 10m, 15m, and 20m. Trade-offs compared to a dedicated single-band Yagi:
- Reduced gain on each band — typically 5–6 dBd rather than the 7 dBd of an optimized single-band design
- Narrower bandwidth on each band — the traps limit the usable SWR range
- Trap losses — the resonant circuits in each trap dissipate a small percentage of power as heat
- More complex construction and more failure points — waterproofing the traps is critical
- For most operators the 3-band coverage trade-off is worthwhile — one antenna and one feedline for three bands
Interlaced Yagis and Fan Beams
An alternative to traps is interlacing separate Yagi element sets for different bands on the same boom. Each band has its own dedicated full-length elements — no traps, no compromise on element length. The elements for different bands are interleaved along the boom and interact with each other electromagnetically, requiring careful optimization to prevent mutual detuning.
- Higher gain per band than trap designs — closer to the theoretical maximum for each element count
- Wider bandwidth per band — no traps to limit frequency range
- More complex design — requires NEC2 modeling of the complete multi-band structure to verify element interaction
- Longer boom typically required — more total elements on the boom
- Examples: Cushcraft A3S, Mosley TA-33, Force-12 C-3 and similar designs
What Makes OWA Different
The OWA (Optimum Wideband Antenna) design, developed by N6LF and later refined by KL7UW, achieves a 50Ω direct feedpoint impedance across an entire amateur band without any matching network. This is accomplished by optimizing the spacing and lengths of the first director relative to the driven element to control the feedpoint impedance independently of the gain-optimization.
In a standard Yagi, the driven element feedpoint impedance is approximately 25Ω — requiring a gamma match or similar. In the OWA design, the first director is spaced very close to the driven element (approximately 0.04–0.06λ), which raises the feedpoint impedance to 50Ω while maintaining good gain and F/B ratio.
- Direct 50Ω feed — coax connects directly to the driven element with a 1:1 current choke, no matching network
- SWR below 1.5:1 across the full band — excellent for wide HF bands like 20m (14.0–14.35 MHz)
- Gain typically 0.5–1 dBd less than a maximum-gain Yagi of the same element count
- Very popular for homebrew Yagis where field-adjustable matching networks add complexity
OWA Design Process
OWA designs are best created through NEC2 optimization rather than scaled from fixed-ratio tables, because the optimum first-director spacing is sensitive to element diameter. The general process:
- Start with a standard NBS 3-element layout as the initial geometry
- Move the first director close to the driven element — start at 0.05λ spacing
- Use 4NEC2's optimizer to vary all element lengths and the first director spacing while targeting: 50Ω feedpoint, SWR below 1.5:1 across the band, and maximum gain
- Verify the design holds up across the full frequency range by running a sweep from band edge to band edge
- Add more directors for additional gain while maintaining the 50Ω wideband feedpoint characteristic
Pre-optimized OWA designs for most common amateur bands are available from the VK2ABQ and ON4UN websites — search for "OWA Yagi" plus your target band and element count. These can be scaled to your exact element diameter using NEC2.
4NEC2 guide for Yagi optimization →Building a 5-Element 2m Yagi for Satellite and Weak Signal
Aluminum tubing boom and elements, gamma match feed, NanoVNA verified — approximately 10 dBd gain on 144 MHz.
Model the Design First
Enter the 5-element geometry into MMANA-GAL or 4NEC2 with your actual element diameter (typically 3/16" or 1/4" rod). Optimize element lengths and spacings for your target frequency (144.200 MHz for SSB weak signal, 145.900 for FM satellite). Verify modeled gain, F/B ratio, and SWR across 144–148 MHz before purchasing materials.
Cut the Boom
Cut a 3/4" square aluminum boom to the total boom length from your model. Mark element positions on the boom with a permanent marker and center punch each position. Drill element holes perpendicular to the boom using a drill press for accuracy — hand drilling at VHF introduces position errors that affect Yagi performance. Deburr all holes.
Cut and Install Elements
Cut all parasitic elements (reflector and directors) to the modeled length from your element rod. Apply the boom correction factor — if elements pass through the boom, add the correction length to each element. Parasitic elements pass through the boom and are secured with small aluminum set screws or compression fittings. Apply Noalox to all element-to-boom contact surfaces.
Build the Driven Element and Gamma Match
The driven element is split at center — each half is a separate piece. Mount both halves on an insulating plate (polycarbonate or PTFE) attached to the boom. Fabricate the gamma rod from the same tubing as the elements — approximately 0.04λ long (approximately 2.7 inches on 2m). Mount it parallel to the driven element with a small spacer maintaining 0.007λ gap. Install a 100 pF variable capacitor between the gamma rod end and the coax center conductor.
Initial SWR Sweep and Gamma Adjustment
Connect the NanoVNA. Sweep 140–150 MHz. Observe the impedance on the Smith chart. Adjust the gamma capacitor to minimize reactance. If the resistive component is below 50Ω, shorten the gamma rod slightly. If above 50Ω, lengthen it. Iterate — each adjustment interacts with the others. Target: SWR below 1.3:1 at center frequency, below 1.5:1 across 144–148 MHz.
Install the Current Choke
Wind 6–8 turns of the coax through an FT-240-31 toroid immediately at the driven element feedpoint. Secure the choke to the boom with UV-resistant cable ties. Run the coax along the boom toward the mast end, securing every 18 inches. Leave a service loop of 12 inches at the mast end before the coax descends — this accommodates rotator rotation without stressing the connector.
Weatherproof and Final Verification
Seal the gamma capacitor enclosure and all feedpoint connections with self-amalgamating tape. Apply silicone sealant to the element-to-boom set screw holes to prevent water ingress. Perform a final SWR sweep at the bottom of the coax run — account for the coax electrical length when interpreting results. Compare the measured SWR to the modeled prediction. Agreement within 10% on impedance confirms a valid build.
How much gain does a Yagi actually add in practice?
A 3-element Yagi with ~7 dBd of gain makes your 100-watt radio perform like a 500-watt station in the antenna's forward direction. On receive, it provides the same 7 dBd improvement — signals that were previously buried in noise become readable. In real-world operating, a 7 dBd Yagi is the difference between working a station 90% of the time versus 30% on marginal propagation paths. The gain is real, measurable, and more impactful than any other single station improvement available at similar cost.
Does a Yagi need to be pointed directly at the target station?
Not exactly. A typical 3-element Yagi has a half-power beamwidth of approximately 60–70 degrees — signals within 30–35 degrees of the beam heading receive nearly full gain. Being 30 degrees off the optimum bearing costs only about 3 dB compared to pointing directly at the target. For casual operating, pointing within 20–30 degrees of a target direction is usually sufficient. For weak-signal work and EME, precise pointing matters more — a 2m EME Yagi with 15 dBd gain has a much narrower beamwidth and precise pointing becomes critical.
What is front-to-back ratio and why does it matter?
Front-to-back ratio (F/B) is the difference in dB between the antenna's gain in the forward direction and the gain directly behind it. A Yagi with 20 dB F/B rejects signals arriving from behind by 20 dB — a 100:1 power ratio. This matters because interfering signals, QRM, and local noise sources often arrive from directions other than the target. During a contest, a high F/B ratio allows working weak DX in Europe while rejecting strong stations calling from the United States on the same frequency. For satellite work, a high F/B reduces terrestrial interference during passes.
Can I build a Yagi without a rotator?
Yes — a fixed Yagi pointed in a favored direction (for example, toward Europe from the eastern US) is a common and effective station configuration. Many contest operators use two or three fixed Yagis pointing in different directions and switch between them. For satellite work on low-orbit birds, manual pointing (holding and rotating the antenna by hand during a 10-minute pass) is a standard technique for portable and lightweight stations. A rotator becomes essential when you want coverage in all directions or need to track moving targets precisely.
What is the difference between a Yagi and a log-periodic antenna?
A Yagi is a single-frequency-optimized design — it delivers maximum performance at its design frequency but degrades significantly off-frequency. A log-periodic (LPDA) is frequency-independent — it provides consistent gain and pattern across a wide frequency range (multiple octaves for some designs) by using many driven elements of varying length and spacing. For most amateur radio applications, a Yagi provides more gain on a single band than an LPDA of similar size. The LPDA wins when covering multiple bands from one antenna is required without the compromises of trap designs.
Log periodic antenna guide →How do I know if my Yagi is performing correctly after installation?
Three checks: First, SWR sweep with a NanoVNA — confirm resonance at the target frequency and SWR below 1.5:1 across the band. Second, use the Reverse Beacon Network (RBN) — transmit CW on the band and compare spot strength in the forward direction versus rearward; the F/B ratio should be clearly visible in the spot strengths. Third, compare against a known antenna using WSPR — alternate between the Yagi and a reference dipole hourly for several days and compare average SNR reports from stations in the beam heading.
Reverse Beacon Network guide →What tower height is needed for a Yagi on 20m?
For competitive DX performance on 20m, the target is to get the antenna to at least λ/2 height — about 35 feet. At this height a 3-element Yagi produces a takeoff angle of approximately 14 degrees. Going to 70 feet (λ) lowers the takeoff angle to around 7 degrees and produces a meaningful additional DX advantage. Many competitive contest stations aim for 70–100 feet on 20m. Below 25 feet, the Yagi's radiation pattern is dominated by the low height rather than the antenna design — a dipole at 25 feet often outperforms a Yagi at 15 feet because the height disadvantage more than cancels the gain advantage.
Is a Yagi suitable for satellite operation?
Yes — a crossed Yagi (two Yagis at 90° on the same boom with a phasing harness for circular polarization) is the standard antenna for LEO amateur satellite operation on 2m and 70cm. Circular polarization eliminates the fading caused by satellite tumbling (spin fading) and Faraday rotation. A 5-element 2m Yagi and 9-element 70cm Yagi on a cross-boom, aimed manually during a pass, is the typical lightweight satellite station configuration. For higher-orbit satellites and linear transponders, larger fixed Yagis or dish antennas are used.
Dual-band satellite array guide →