Antennas · Volume 11
Yagi-Uda Antennas
Director/reflector/driven-element design, boom length vs gain, F/B optimization, single-band vs LFA/OWA, hairpin and gamma matches; the canonical gain antenna for VHF/UHF and the secret weapon at 2.4 / 5 GHz
Contents
1. About this volume
A Yagi-Uda is the antenna you build when you know what direction you want gain. The 1926 Hidetsugu Yagi and Shintaro Uda paper at Tohoku Imperial University identified the parasitic-array principle that has dominated directional VHF/UHF antennas for a century: a half-wave driven element surrounded by a small number of close-spaced parasitic conductors produces dramatic forward gain (5–15 dB) and front-to-back ratio (15–35 dB) at modest mechanical and electrical cost. Every TV antenna ever bolted to a rooftop is a Yagi. Every 2 m repeater that someone aims a beam at is fed by a Yagi. Every 2.4 GHz Wi-Fi link that crosses a kilometer of open space is using a Yagi (or a parabolic dish — Vol 13). Every EME (earth-moon-earth) station uses a stack of large Yagis.
This volume covers the Yagi family at engineer-grade depth. The geometric design space is well-understood (60+ years of NEC modeling has refined the element spacings to optimal values); the manufacturing problem is well-understood (every major antenna manufacturer makes Yagis); and the operational tradeoffs are well-understood. What’s left for the operator is to pick the right Yagi for the use case and to install it cleanly. This volume aims to make those decisions informed.
A note on scope: this volume covers Yagis in the traditional sense — parallel-element parasitic arrays with discrete reflector, driven, and directors. Closely-related directional antennas include log-periodic dipole arrays (LPDA — Vol 13 §3), which superficially resemble Yagis but operate on a different principle (every element is active, not just the driven), and quagi / loop-Yagi designs (folded-loop driven element + Yagi-style parasitics — covered here in §7). Yagis paired with stacks (multiple Yagis combined in phase for additional gain) are covered briefly in §11; the “Yagi stack as a phased array” topic gets deeper treatment in Vol 32 (Antenna farms).
2. Geometry & theory — the parasitic-array principle
2.1 How a parasitic element steers radiation
A driven element radiates a clean dipole pattern in free space — broadside figure-8, peak gain 2.15 dBi. Place a passive conductor near the driven element (within ~0.25 λ), and the passive conductor re-radiates a portion of the incident field. The phase of the re-radiated wave depends on the passive conductor’s electrical length:
- A conductor slightly longer than λ/2 is inductively reactive — the re-radiated wave is delayed in phase, behaving like a reflector
- A conductor resonant at λ/2 re-radiates in phase with the driven element
- A conductor slightly shorter than λ/2 is capacitively reactive — the re-radiated wave leads in phase, behaving like a director
Add a reflector behind the driven element and a director (or several) in front, and the spatial sum of all the re-radiated waves produces constructive interference forward and destructive interference backward. The pattern collapses from a figure-8 into a forward-pointing oval lobe with substantial gain and a deep rear null.
Side view of a 5-element Yagi (boom going left → right):
rear (away from desired direction) forward
↓ ↑
reflector ● driven ● d1 ● d2 ● d3 ● forward gain
(5% longer (resonant) (4% shorter than driven each)
than driven)
←──── 0.2λ ────→
(typical reflector-to-driven spacing)
spacing between directors:
d1: 0.15λ from driven
d2: 0.2λ from d1
d3: 0.25λ from d2
(spacing grows toward the tip)2.2 The phase-and-spacing tradeoff
A Yagi’s gain and pattern are governed by:
- Driven element length (sets resonance and feedpoint Z)
- Reflector length (typically 5% longer than driven; the standard “+5%” rule)
- Director lengths (each progressively shorter; typical drop is 1–4% per director)
- Element spacing (varies along the boom — typically 0.15λ to 0.35λ between consecutive elements)
- Element diameter (affects resonant length corrections — fatter elements need 5–15% less length)
The design space is multi-dimensional, and the “right” optimization depends on what you’re maximizing: peak gain, F/B ratio, bandwidth, sidelobe suppression, or some weighted combination. NEC-2 / NEC-4 modeling (Vol 28) lets you explore the design space numerically before cutting metal.
The community has converged on a few canonical Yagi designs that are well-optimized for amateur use:
- DL6WU 144 MHz Yagi designs (Günter Hoch DL6WU): 16-element through 32-element EME-grade designs that have been re-measured and verified countless times
- K1FO 144 MHz designs: variant of DL6WU with optimized side-lobe suppression
- G0KSC LFA series: loop-fed Yagi-Uda with natural 50 Ω match
- WA5VJB Cheap Yagi: a low-cost 3-element 2m Yagi for portable use
- OWA designs (M2 Antennas, Force 12): optimized for wide bandwidth at modest gain sacrifice
For any given gain target, the “right” Yagi design is usually one of these well-optimized published designs — building from scratch by guessing element lengths is wasted effort when proven designs exist.
2.3 Why Yagis are mechanical-only
A Yagi has no resonant tuning step in the field — the geometric dimensions ARE the tuning. Once you’ve built the antenna correctly (element lengths and spacings to spec), the SWR and pattern are determined by physics. There’s no “adjust the resistors” or “tune the LC tank” step. The only field-tuning involves the matching network (§6) which couples the driven element to the coax.
This is the Yagi’s design-vs-operation discipline: spend time getting the dimensions right, and the antenna works for its lifetime. Cut elements quick-and-dirty, and the antenna will be off the design and the gain will be ~3 dB below spec. The high-end Yagi manufacturers (M2, Force 12, InnovAntennas) provide precision-machined elements with milled length and spacing tolerances that maintain the design’s promised gain across temperature and weather variation.
3. The three element types — driven, reflector, director
3.1 The reflector
A reflector is one element placed behind the driven element (in the direction opposite to the desired beam). Its length is typically 5% longer than the driven element (e.g. for a 144 MHz Yagi: driven at ~995 mm, reflector at ~1043 mm). The reflector’s inductive reactance produces a re-radiated wave that adds constructively to the driven element’s forward radiation and destructively to its rearward radiation.
One reflector is enough. Adding a second reflector (“double reflector”) behind the first produces minor gain improvements (<0.5 dB) at significant mechanical and beamwidth cost. Most Yagi designs use exactly one reflector.
3.2 The driven element
The driven element is the antenna’s only fed component. Its length is ~λ/2 minus a small correction for the parasitic-element interaction (typically 1–3% shorter than a free-space half-wave). The feedpoint Z drops below the free-space 73 Ω because the parasitic elements load the driven element capacitively — feedpoint Z is typically 25–35 Ω for a 5-element Yagi, 18–25 Ω for a 9-element Yagi, 12–18 Ω for a 15-element design.
The driven element’s form depends on the matching scheme:
- Simple straight dipole: needs a matching network (gamma, hairpin, T-match)
- Folded dipole: 4× the impedance of a simple dipole — useful as a step-up to 50 Ω
- LFA loop: a rectangular loop driven element — natural 50 Ω match without external network
- Quad-Yagi (“quagi”): a square or diamond loop driven element + Yagi-style directors
3.3 The directors
Directors are passive elements forward of the driven element. Each is progressively shorter (by 1–4% per element); spacing grows from ~0.15λ between driven and first director up to ~0.40λ between the last two directors (for very long Yagis). The total number of directors varies from 1 (in a 3-element design) to 20+ (in long EME-grade Yagis).
The gain contribution per director:
- 1st director: +1.5 to +2.0 dB
- 2nd director: +0.8 to +1.2 dB
- 3rd director: +0.5 to +0.8 dB
- 4th–6th directors: +0.3 to +0.5 dB each
- 7th–10th directors: +0.2 to +0.3 dB each
- 11th–20th directors: <0.2 dB each
The diminishing-returns curve is steep. Most amateur applications stop at 5–9 elements; EME stations might go to 15–25 elements per Yagi (and stack four of them).
4. Boom length vs gain — the diminishing-returns curve
The classic Yagi-gain rule of thumb:
gain (dBd) ≈ 10 × log₁₀(boom length in λ) + 7
This formula works well from 2-element (boom ~0.15λ) to 20-element (boom ~6λ) designs. Examples:
| # elements | Boom length (λ) | Gain (dBd) | Gain (dBi) | HPBW |
|---|---|---|---|---|
| 2 (driven + reflector) | 0.15 | 4.5 | 6.65 | 75° |
| 3 (driven + reflector + 1 director) | 0.40 | 6.5 | 8.65 | 60° |
| 4 | 0.70 | 7.5 | 9.65 | 55° |
| 5 | 1.0 | 9.0 | 11.15 | 50° |
| 6 | 1.3 | 9.7 | 11.85 | 45° |
| 7 | 1.6 | 10.3 | 12.45 | 42° |
| 8 | 1.9 | 10.8 | 12.95 | 38° |
| 9 | 2.2 | 11.2 | 13.35 | 35° |
| 11 | 2.8 | 11.9 | 14.05 | 30° |
| 15 | 4.0 | 13.0 | 15.15 | 22° |
| 20 | 5.5 | 14.0 | 16.15 | 17° |
| 28 | 8.0 | 15.0 | 17.15 | 12° |
A 5-element Yagi (~11 dBi gain, 50° beamwidth) is the amateur sweet spot — substantial gain, manageable boom, broad enough beamwidth that you don’t need precision aiming. A 15-element Yagi (~15 dBi, 22° beamwidth) is the next major step up; it requires a rotator for any non-fixed direction and the longer boom is mechanically more demanding.
4.1 The 3 dB per doubling rule
Doubling the boom length adds approximately 3 dB of gain (slightly less at the long-boom end where the rule starts breaking down). Going from a 5-element to a 10-element doubles the boom and adds ~3 dB; going from 10-element to 20-element does the same. Compare:
| Step | Boom length change | Gain added |
|---|---|---|
| 3-el → 5-el | 0.4λ → 1.0λ (2.5×) | 2.5 dB |
| 5-el → 7-el | 1.0λ → 1.6λ (1.6×) | 1.3 dB |
| 7-el → 11-el | 1.6λ → 2.8λ (1.75×) | 1.6 dB |
| 11-el → 15-el | 2.8λ → 4.0λ (1.4×) | 1.1 dB |
| 15-el → 28-el | 4.0λ → 8.0λ (2.0×) | 2.0 dB |
The diminishing-returns curve gets steeper at longer boom lengths. A 28-element EME Yagi has 8λ of boom (~16.6 m at 144 MHz, ~5.5 m at 432 MHz). That’s a significant mechanical structure.
4.2 The “stacking” alternative to long booms
Instead of doubling the boom length for +3 dB, you can stack two Yagis vertically and feed them in phase. Stacking two identical Yagis at ~0.6λ vertical spacing produces ~+3 dB gain (the array-of-two factor) at the cost of doubling the antenna count and adding a power-divider feed network.
Stacking has a higher front-to-back-ratio improvement than long booms (the stacked pattern is sharper in elevation, which is what EME and meteor-scatter operators want), but stacking adds:
- 2× cost (two antennas instead of one)
- A power divider (1/2 wavelength of coax, properly impedance-matched)
- A phasing harness with strict length tolerance
Decision matrix:
- “I need +3 dB and I have horizontal space”: longer boom
- “I need +3 dB and I have vertical space and rotators”: stack two Yagis
- “I need +6 dB”: stack four Yagis (the “EME array” — 2×2 array of long-boom Yagis)
5. Front-to-back ratio and side-lobe suppression
Front-to-back ratio (F/B) is the ratio of forward-direction gain to gain in the opposite direction (180° behind the antenna). A high F/B means the antenna is “rejecting” signals from behind it — useful for reducing back-side interference from cities, repeaters, or noise sources.
5.1 Typical F/B values
| # elements | Optimized F/B |
|---|---|
| 2 | 8–12 dB |
| 3 | 15–18 dB |
| 5 | 22–27 dB |
| 7 | 25–30 dB |
| 9 | 27–32 dB |
| 15 | 28–35 dB |
F/B improvements above 30 dB typically require trading gain or bandwidth — you can’t have peak gain AND peak F/B AND wide bandwidth simultaneously. Most modern designs target ~25 dB F/B with comfortable bandwidth and accept that the last 5 dB of F/B requires specialized side-lobe-suppressed designs.
5.2 The three-way design tradeoff
For any given boom length, three design objectives are in tension:
Maximum Gain (peak forward radiation)
●
│
│
│
│
│
●───────────────────────────────●
Wide Bandwidth Maximum F/B
(2:1 SWR over wider range) (deepest backward null)
"Pick two of three"- Peak-gain optimization: highest forward gain, modest F/B (~22 dB), narrowest bandwidth (~3%)
- F/B optimization: optimized backward null (~30 dB), 0.5–1 dB gain sacrifice, narrowest bandwidth
- Bandwidth optimization (OWA — Optimized Wideband Antenna): widest bandwidth (~8–12%), 1 dB gain sacrifice, modest F/B
The OWA designs (M2 Antennas, Force 12, InnovAntennas’ wide-band series) sacrifice ~1 dB of peak gain for a flatter SWR across the entire band — useful for multi-frequency operations (FM/SSB/CW on a single band) or contesting where the operator doesn’t want to retune the antenna.
5.3 Side-lobe suppression
A Yagi’s pattern has side lobes at angles other than the main beam. For typical Yagis, the first side lobe is at ~50–80° off the main beam axis and is 10–15 dB below peak gain. Suppressing these side lobes is important for:
- EME (earth-moon-earth) where unwanted ground-pickup is the noise floor
- Radio astronomy where any extraneous signal contaminates the measurement
- Specialized contest applications where back-and-side QRM (interference) is the limiting factor
Side-lobe suppression usually trades against gain (~0.5 dB sacrifice for 10 dB improvement in worst-case side lobe).
6. Feedpoint impedance and matching — direct, gamma, hairpin, T-match, LFA loop
6.1 The impedance problem
A driven element loaded by parasitic elements presents an impedance significantly lower than the free-space 73 Ω. For a 5-element Yagi at 50 MHz–150 MHz, the feedpoint Z is typically 25–35 Ω. This needs to be transformed to 50 Ω for the coax feedline.
Five common matching schemes, ranked by complexity:
6.2 Direct feed
If your driven element’s impedance happens to be 50 Ω (some designs are deliberately tuned to this point at the cost of some gain), you can feed it directly with coax. A 1:1 current BALUN at the feedpoint suppresses common-mode currents. Direct feed is mechanically simplest but limits the designer’s freedom to optimize gain — the driven-element length and surrounding director spacings have to be chosen for the 50 Ω target.
6.3 Gamma match
A gamma match uses a series capacitor + a parallel tap on the driven element. Adjustable both for impedance match and phase. Pros: very compact, no balun required. Cons: needs adjustment in the field (tedious), the capacitor can fail in weather, can have a slight pattern asymmetry (the gamma “rod” perturbs the driven element).
Gamma matches were standard on 1970s–1990s amateur HF Yagis (Cushcraft, Wilson, Hy-Gain). Less common today; the LFA loop (§6.6) is the modern replacement.
6.4 Hairpin match
A hairpin match is a U-shaped wire stub between the driven element terminals, sized for the target impedance match. No adjustment after construction; the geometry sets the match. Pros: zero adjustment, robust, no capacitor to fail. Cons: less flexible than gamma, harder to manufacture precisely.
Hairpin matches are popular on commercial high-end Yagis (Force 12, M2 Antennas) where the manufacturer wants a “build once, no field adjustment” design.
6.5 T-match
A T-match is the symmetric version of a gamma — two parallel taps + two series caps. Used on balanced-feedpoint Yagis (a few HF designs); the gamma is more common in the 50 MHz+ range.
6.6 LFA loop (Justin Johnson G0KSC)
The LFA (Loop-Fed Yagi) design has a folded-loop driven element with a 50 Ω natural feedpoint — no matching network needed at all. The loop’s impedance is naturally close to 50 Ω; no transformer, no capacitor, no fussy gamma adjustment.
The LFA was patented by Justin Johnson G0KSC around 2005 and has become the dominant amateur Yagi design philosophy. Most modern Yagis (~2015 and later) use LFA driven elements. The trade: the LFA driven element is mechanically more complex than a simple dipole, but the elimination of the matching network is a significant simplification overall.
6.7 Match comparison table
| Match | Impedance flexibility | Adjustment needed | Manufacturing cost | Typical Yagi era |
|---|---|---|---|---|
| Direct feed | Single Z point | None | Lowest | 1980s+ (limited) |
| Gamma | Wide range | High | Moderate | 1960s–2000s |
| Hairpin | Wide range | None | Moderate-high | 1990s+ |
| T-match | Wide range | High | Moderate | Rare (specialized) |
| LFA loop | 50 Ω native | None | High | 2005+ |
7. Single-band vs LFA vs OWA topologies
7.1 Single-band traditional Yagi
The classic Yagi-Uda design: optimized for narrow bandwidth (3–5% for 2:1 SWR), peak forward gain, and modest F/B. Used on commercial single-band Yagis (typically the 50 MHz–432 MHz family). Cushcraft, Wilson, Hy-Gain produced this style for decades.
Trade-offs: optimal gain at center frequency; bandwidth limitations require precise frequency-locked operation (no SSB/AM/FM mixing across a wide band).
7.2 OWA (Optimized Wideband Antenna)
OWA designs (popularized by M2 Antennas) sacrifice 0.5–1 dB of peak gain for 8–12% bandwidth at 2:1 SWR. Useful for:
- 2 m amateur band (the full 4 MHz from 144–148 covered without re-tuning)
- 6 m amateur band (the full 4 MHz from 50–54 covered without re-tuning)
- 70 cm wide-coverage operation (430–450 MHz)
The OWA’s wider bandwidth is achieved through NEC-optimized element spacings and lengths that flatten the impedance curve across the band.
7.3 LFA (Loop-Fed Yagi)
LFA designs combine the OWA-style wide bandwidth with the natural 50 Ω match of the loop-fed driven element. Modern LFA designs are common across the spectrum:
- HF LFA (e.g. InnovAntennas 50LFA-5 — 5-element 6 m LFA)
- VHF LFA (e.g. InnovAntennas 144LFA-9)
- UHF LFA (e.g. G0KSC’s published designs)
The LFA is the modern amateur Yagi default — high gain, wide bandwidth, no matching network, robust under weather and temperature variation.
7.4 Quad-Yagi (“quagi”)
A quagi has a quad-loop driven element (a square or diamond loop of wire) + Yagi-style parasitic elements. The quad-loop offers slightly better F/B than a dipole-driven Yagi (the loop’s inherent pattern is cleaner) at the cost of mechanical complexity (the loop needs spreaders and tensioning).
Quagis were popular in the 1990s–2000s for 144 MHz / 432 MHz EME. Modern LFA designs have largely replaced them for most amateur use.
8. Radiation pattern — azimuth, elevation, HPBW
8.1 Pattern characteristics
A Yagi’s pattern is a forward-pointing main lobe with:
- Half-power beamwidth (HPBW): typically 30–60° azimuth for amateur Yagis
- Elevation pattern: depends on antenna height above ground (similar lobing to a dipole, see Vol 6 §4.2)
- F/B ratio: 15–35 dB (see §5)
- Side lobes: typically 10–18 dB below main beam
8.2 HPBW by element count (typical 50 MHz+ Yagis at horizon)
| # elements | Azimuth HPBW | Elevation HPBW | Sidelobes |
|---|---|---|---|
| 2 | 75° | wide | not relevant |
| 3 | 60° | ~75° | -10 dB |
| 5 | 50° | ~60° | -12 dB |
| 7 | 42° | ~52° | -14 dB |
| 9 | 35° | ~45° | -15 dB |
| 15 | 22° | ~28° | -18 dB |
| 28 | 12° | ~16° | -20 dB |
The 15-element Yagi’s 22° HPBW means a 30° aiming error costs ~6 dB of signal — significant. EME and serious DX work require rotators with ≤2° accuracy and a controller with calibration features. Amateur HF / VHF / UHF mobile operation uses shorter Yagis with broader patterns to relax the aiming requirements.
8.3 Aiming considerations
A Yagi requires aiming for the wanted signal direction. The community has converged on two approaches:
- Fixed Yagi: pointed at the most-important direction (a favored repeater, a DX path). The 22-element Yagi pointed at the moon for EME is the canonical example.
- Rotated Yagi: mounted on a rotator that lets the operator aim to any direction. Yaesu G-450 / G-1000 / G-2800 family, Hy-Gain T2X / Ham-IV, Prosistel rotators are standard.
Rotators add cost ($300–1500), maintenance, and a control cable. For amateur use, a 3-el or 5-el Yagi on a 6 ft mast aimed at a permanent station is fine; a 9-el+ Yagi on a 30 ft tower needs a rotator.
9. Frequency response & SWR curve
9.1 Standard Yagi bandwidth
| Design | 2:1 SWR bandwidth | Typical F/B at band edges | Notes |
|---|---|---|---|
| Single-band traditional | 3–5% | 5–10 dB worse | Narrowband peaked |
| OWA | 8–12% | 10–15 dB worse | Wide-band optimized |
| LFA | 8–12% | Similar to OWA | Natural 50 Ω + wide |
| Multi-band trap Yagi | 5–8% per band | varies | Per-band trap loading |
For amateur 2 m operation (144–148 MHz, 2.8% of band center), a single-band traditional Yagi easily covers the band. For 6 m operation (50–54 MHz, 7.7% of band center), an OWA design is typically required to maintain SWR across the band.
9.2 The bandwidth-vs-gain question
Designing a Yagi for maximum peak gain produces a narrowband antenna. Designing for maximum bandwidth produces lower peak gain. The two requirements pull in opposite directions:
- Peak-gain design: directors closely spaced, element lengths precisely optimized → 4–5% bandwidth, 0.5 dB more peak gain
- Wideband design (OWA): spacing relaxed, elements slightly off-resonance → 8–12% bandwidth, 0.5 dB peak-gain sacrifice
The decision depends on the operating style. SSB/CW operators on narrow bands: peak-gain design. Wideband operators (SSB + FM + AM + digital across a 4 MHz band): OWA. Most amateurs land on OWA for the flexibility.
10. Best-case use
- Point-to-point links (Wi-Fi remote, ham repeater access, EME, meteor scatter, weak-signal): a Yagi pointed at a known destination gives 10–20 dB more signal than an omnidirectional vertical, which is often the difference between “works” and “doesn’t.”
- Direction-finding receive: a Yagi’s directional pattern with sharp nulls is excellent for locating signal sources. Better than a small loop for VHF/UHF (the Yagi’s narrow beam isolates the bearing more precisely).
- Contest VHF/UHF: gain + directivity wins. A 9-element 144 MHz Yagi vs an omni vertical: 12 dB of advantage per QSO.
- Satellite communication (RHCP-configurable Yagis): two Yagis crossed at 90° produce circularly-polarized radiation for satellite uplink/downlink work.
- Wi-Fi long-distance (with a 2.4 GHz Yagi): repeated 5+ km Wi-Fi links use Yagis routinely. Direct line-of-sight + Yagis at both ends + outdoor weatherproof radios = a 5 km link.
- Wireless security auditing at distance: a 2.4 GHz / 5 GHz Yagi mated to a directional Wi-Fi attack platform (WiFi Pineapple or AWOK Dual Touch V3) extends the attack/audit range from line-of-sight to 1+ km. Site survey from a fixed observation point.
- Public-safety / emergency comms: a directional 2 m or 70 cm Yagi pointed at a regional repeater extends the comms range substantially.
11. Worst-case use
- Omnidirectional coverage: a Yagi’s narrow pattern is the opposite of omnidirectional. For scanning, all-direction Wi-Fi, or any application where the signal source’s direction is unknown, use a discone (Vol 12) or vertical (Vol 8).
- HF with backyard space limits: a 3-element 20 m Yagi has a 24 ft boom. Most residential lots can’t accommodate this. HF Yagis are tower-mounted with rotators; 80 m / 160 m Yagis are essentially impossible for amateur installations (boom lengths approach 100 ft).
- Mobile operations: a Yagi on a vehicle is mechanically impractical. Mobile Yagis exist (Hustler-style portable 6m Yagi, MFJ-1844 6m Yagi) but they’re set-up-stop operations, not while-driving.
- Indoor: an indoor Yagi’s pattern is corrupted by walls, ceilings, and metallic objects. Use a J-pole or roll-up dipole instead.
- Multi-direction operation without a rotator: aiming a fixed Yagi at the most-common direction is fine; if you need to work multiple directions, get a rotator or use an omnidirectional antenna.
- Mountain-top portable (SOTA/POTA): a Yagi can be packed (Arrow 144-3 portable Yagi, ~1 kg) but the deploy time is 5+ minutes vs a roll-up J-pole’s 30 seconds. SOTA operators typically pick simpler antennas unless they’re doing serious VHF DX.
12. Power handling
A Yagi’s power handling lives in three places:
| Limit | Typical max continuous |
|---|---|
| Element conductor (1/2″ aluminum tubing) | 2–5 kW |
| LFA loop construction | 5+ kW (the loop is robust) |
| Gamma-match capacitor | 1–2 kW (depending on cap rating) |
| Hairpin-match (no cap) | 5+ kW (limited by elements) |
| 1:1 BALUN at feedpoint | 1.5 kW typical (Mix 31, 2.4″ toroid) |
| 4:1 BALUN (for folded-dipole feeds) | 1.5 kW typical |
| RG-8 coax (for high-power Yagis) | 1 kW at HF, 500 W at 2 m |
For amateur amplifier (1.5 kW) operation through a Yagi, the BALUN is usually the limit; the elements and matching network easily handle full legal limit. For multi-kW commercial broadcast use, the elements and matching are sized up correspondingly.
Specific commercial Yagi power ratings (mid-2026):
| Yagi | Power rating | Notes |
|---|---|---|
| Diamond A144S5 (5-el 2m) | 800 W | Budget commercial |
| Comet CYA-1216E (16-el 1.2 GHz) | 250 W | Diamond’s 1.2 GHz line |
| M2 Antennas 2M9SSB (9-el 2m) | 2 kW | High-quality commercial |
| InnovAntennas LFA-50/9 (9-el 6m) | 5 kW | Loop-fed LFA, high-power |
| DX Engineering DX-LB-MS (4-el 20m) | 2 kW | HF Yagi |
| SteppIR DB18E (4-band rotatable HF) | 3 kW | Premium motorized HF |
| Force 12 Magnum 6 (6-band HF) | 4 kW | Top-tier HF |
13. DIY build — a 5-element 2 m Yagi from EME-class plans
This is a serious amateur-grade Yagi for 144 MHz. About 4 hours of work plus careful tuning. Total parts cost ~$120 USD.
13.1 Geometry (K1FO 5-element 144.1 MHz)
The K1FO 5-element 144.1 MHz Yagi (Steve Powlishen K1FO, optimized 1990s) is the canonical “EME-class small Yagi” — exceptional cleanliness for its size, ~9 dBd gain, 23 dB F/B.
| Element | Length | Position on boom (from reflector) |
|---|---|---|
| Reflector | 1043 mm | 0 mm |
| Driven | 990 mm (with hairpin match) | 380 mm |
| Director 1 | 950 mm | 690 mm |
| Director 2 | 930 mm | 1080 mm |
| Director 3 | 920 mm | 1690 mm |
| Boom length | 1690 mm |
All elements: 1/2″ (12 mm) aluminum tubing. Boom: 1.5 m of 1″ × 1″ aluminum tube. Element-to-boom insulators: insulating mounts (DX Engineering EMP1 or commercial equivalents).
13.2 Bill of materials
| Part | Specification | Source | Mid-2026 price |
|---|---|---|---|
| Aluminum tubing for elements | 1/2″ (12 mm) OD, ~5 m total | Texas Towers TT12HD ($1.85/ft) | $30 |
| Boom | 1″ × 1″ × 1.7 m aluminum tube | Texas Towers / local supplier | $25 |
| Element insulators | DX Engineering EMP1 (5 pairs) | $35 | |
| Driven-element split block | Plastic with two terminal screws | $8 | |
| Hairpin match wire | #14 enamel wire, ~30 cm | local | $1 |
| 1:1 current BALUN | Mix-31 FT240-31 with bifilar winding, in weatherproof box | DIY or commercial ($60) | $25–60 |
| SO-239 chassis connector | Bulkhead-mount | DigiKey | $5 |
| Coax pigtail | RG-8X, 1 m | Times Microwave | $15 |
| Hardware | Stainless U-bolts, hose clamps | $10 | |
| Weatherproofing | 3M tapes + Coax-Seal | $8 | |
| Total | ~$150 |
13.3 Step-by-step construction
Cut the elements. Cut all 5 aluminum elements to their specified lengths exactly. Element-length tolerance for a 144 MHz Yagi is about ±1 mm — careless cutting will shift the design’s gain peak off 144.1 MHz. Use a chop saw with a stop, not a hacksaw.
Drill mounting holes. Each element gets a hole through its center for the boom-mount bolt. Use a drill press; the holes must be at the element’s geometric center for the element to be electrically symmetric.
Assemble the boom. Mount the 5 elements on the boom at the spec’d positions. The driven element gets the split-block holder (which lets the two halves be connected to the feedpoint terminals).
Install the hairpin match. Solder a U-shape of #14 enamel wire between the two driven-element terminals, sized to ~25 mm wide × 100 mm tall (this is a starting point; final dimensions adjusted during tuning).
Install the BALUN. Mount the 1:1 BALUN box at the feedpoint. Connect the two driven-element terminals to the BALUN’s balanced side; the coax connector on the BALUN’s unbalanced side accepts the feedline.
Sweep with NanoVNA. Connect the coax to the BALUN, then the NanoVNA to the coax. Sweep 140–150 MHz. Target: SWR < 1.5:1 at 144.0–145.0 MHz, < 2:1 across 144.0–146.0 MHz.
Adjust the hairpin. If SWR is high, adjust the hairpin’s width and/or height by 5 mm increments. Each adjustment shifts the match slightly. Once SWR < 1.3:1 at the target frequency, lock in the geometry with solder or epoxy.
Trim elements if needed. If the gain peak is at the wrong frequency (e.g. 143.5 MHz instead of 144.1), trim the directors slightly. Element-length tolerance is tight; usually no trimming is needed if you cut to spec.
Mount the antenna. Bolt to the mast at the boom-to-mast joint (typically using a U-bolt and an insulating bracket if the boom is grounded for lightning).
13.4 Tuning verification
A successful K1FO 5-element 144 MHz Yagi shows:
- SWR < 1.5:1 across 144.0–145.0 MHz
- SWR < 2:1 across 144.0–146.0 MHz
- F/B (measured by comparing forward vs reverse signal strength on a distant fixed source) > 20 dB
- HPBW ~50° (verifiable by rotating the antenna and measuring received signal at a fixed distant source)
- No anomalous resonances (parasitic modes) outside the design band
If the SWR is high (>2:1 at 144.1) even after hairpin adjustment, the driven element length is wrong (recheck the 990 mm dimension).
14. Commercial buys
Sorted by tier and use case (USD, mid-2026):
| Tier | Model | Bands | Price | Notes |
|---|---|---|---|---|
| Budget | Arrow 144-3 (3-el portable 2m) | 2m | $90 | The SOTA-favorite portable Yagi |
| Budget | Diamond A144S5 (5-el 2m) | 2m | $120 | Reliable budget 5-el Yagi |
| Budget | Diamond A430S10 (10-el 70cm) | 70cm | $140 | UHF version of the Diamond family |
| Budget | Comet CYA-1216E (16-el 1.2 GHz) | 1.2 GHz | $150 | Diamond’s 23 cm line |
| Budget | Cheap 2.4 GHz Yagi (LinkSys / generic) | 2.4 GHz | $30–60 | Wi-Fi long-distance |
| Mid | M2 Antennas 2M9SSB (9-el 2m) | 2m | $350 | M2 Antennas’ workhorse 2m Yagi |
| Mid | InnovAntennas 50LFA-5 (5-el 6m LFA) | 6m | $290 | Modern LFA design |
| Mid | InnovAntennas 144LFA-9 (9-el 2m LFA) | 2m | $330 | LFA replacement for older M2 designs |
| Mid | DX Engineering DX-LB-MS | HF (20/15/10m) | $850 | DX Engineering’s 3-band HF Yagi |
| Mid | Hy-Gain TH-3JRS (3-el 20/15/10m) | HF tribander | $620 | Older but proven tribander |
| Premium | M2 Antennas 7M9SSB (9-el 7m) | 7m | $480 | Premium 7m design |
| Premium | M2 Antennas 144-15M (15-el 2m, EME-grade) | 2m | $750 | EME-class long-boom |
| Premium | SteppIR DB18E (motorized HF) | HF | $4500 | Motorized 4-band rotatable HF |
| Premium | Force 12 Magnum 5 (5-band HF Yagi) | HF | $4000 | Top-tier HF rotatable |
| Premium | OptiBeam OB16-3WARC | HF (WARC bands) | $5000+ | DX-contest grade |
What to avoid:
- “8–15 dBi Wi-Fi Yagis” priced under $40 — the gain claims are isotropic-with-no-ground references; real measured gain is 3–6 dBi. The cheap Wi-Fi Yagis work, but the dBi claims are wildly inflated.
- “Multi-band miracle Yagis” without published spec sheets — every reputable Yagi manufacturer publishes the design parameters; suspect anything that won’t tell you the element lengths and spacings.
- Used Yagis with corroded element joints — the element-to-boom mechanical contact is critical; corrosion produces variable resistance that ruins the pattern.
15. Companion gear — rotator, mast, coax
A Yagi requires a supporting infrastructure that costs as much (or more) than the antenna itself.
15.1 Rotators
| Rotator | Capacity | Price (mid-2026) | Typical Yagi |
|---|---|---|---|
| Yaesu G-450 / G-1000DXA | Light-duty (3-5 el VHF) | $250–500 | Arrow 144-3, Diamond A144S5 |
| Yaesu G-2800 | Medium-duty (9-el VHF, small HF) | $700 | M2 Antennas 2M9SSB |
| Hy-Gain T2X / Tail Twister | Heavy-duty (HF tribanders) | $750 | Hy-Gain TH-3JRS, similar |
| Hy-Gain Ham IV | Medium-heavy | $550 | Mid-size HF / large VHF |
| Prosistel PST-D71 | Industrial | $1500+ | Large HF Yagis, EME stacks |
| Alfa Spid RAK / RAS | Industrial | $1800+ | Top-tier HF / EME |
The rotator selection is determined by wind load of the antenna, not gain — a high-gain Yagi with a long boom has more wind load than a short-boom Yagi with similar gain.
15.2 Mast
The mast holds the Yagi at the desired height. Typical masts:
- Telescoping aluminum mast (Glen Martin, US Towers, Universal Towers): 5–10 m height, $200–600
- Wood pole / dedicated tower: 10–25 m height, $1000–5000+ (the tower being the main cost)
- Free-standing fiberglass mast (Spiderbeam 12 m or 18 m): 10–18 m, $200–500
For HF Yagis, a tower is usually required (15+ m needed for proper low-angle radiation). For VHF/UHF Yagis, a 5–10 m mast on a roof or yard is sufficient.
15.3 Coax
A Yagi at 144 MHz has 0.5 dB / 30 m loss on RG-8X, 0.3 dB / 30 m on LMR-400, and 0.15 dB / 30 m on Heliax. For long runs at higher frequencies, the coax loss budget becomes significant — a 70 cm Yagi with 30 m of RG-8X has 1+ dB of coax loss, which the operator usually wants to minimize by going to LMR-400 or Heliax. Coax selection in Vol 5 §6.
15.4 Bearing and thrust mount
For tower-mounted Yagis, a separate thrust bearing handles the antenna’s downward force on the rotator’s drive shaft. Cushcraft’s thrust mount, Glen Martin’s RT-936, or DIY arrangements with a ball-bearing flange + thrust collar.
16. Common gotchas and myths
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“Higher gain = better” — true in absolute terms but with a tradeoff. A 15-element 2m Yagi has 15° HPBW; mis-aiming by 30° loses 6 dB. A 5-element 2m Yagi has 50° HPBW; mis-aiming by 30° loses 1 dB. For amateur use without a rotator, the shorter Yagi often delivers more usable signal.
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“All Yagis at the same boom length are equal” — false. Optimization details vary the gain by 2–3 dB. A well-optimized 5-element design (K1FO, DL6WU, LFA) outperforms a poorly-optimized 5-element design by 2+ dB.
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“Element diameter doesn’t matter” — false. Element diameter affects resonant length (fatter elements need ~10–20% less length for the same resonance). The DL6WU and K1FO designs use specific tubing diameters; substituting different sizes shifts the resonant frequencies.
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“I’ll just hang it horizontally outside the window” — VHF/UHF Yagis are very sensitive to nearby reflectors (walls, ceilings, other antennas). A Yagi installed too close to the building structure loses 3–6 dB of forward gain to the asymmetric near-field pickup. Yagis need clear space in front (and ideally behind and to the sides).
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“More elements = more bandwidth” — false. Adding elements narrows the bandwidth. The bandwidth-gain tradeoff is fundamental; OWA designs achieve wide bandwidth at the cost of peak gain.
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“50 Ω LFA loop matches without any tuning” — true if the design is exact. In practice, real LFA Yagis still benefit from a quick SWR sweep + minor element adjustment, but the natural 50 Ω match eliminates the gamma/hairpin adjustment headache.
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“A Yagi pointed straight up gets the most signal from above” — true for direct overhead signals (e.g. a satellite directly overhead), but the Yagi’s pattern is forward-directional, not zenith-directional. For satellites passing overhead but on either side of zenith, the Yagi has to be aimed along the satellite’s track, not straight up.
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“The Yagi’s pattern is the same on every frequency” — true only within the design’s bandwidth. Out-of-band, the pattern degrades — sidelobes climb, F/B drops, gain falls. A 144 MHz Yagi on 432 MHz is a different antenna.
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“Cheaper Yagis are just lower-gain versions of expensive Yagis” — partly false. Cheap commercial Yagis often use mediocre matching networks (lossy gamma matches, imprecise hairpin geometry) that absorb 0.5–1 dB of power and produce less reliable patterns. The gain and pattern of a $300 Yagi typically exceed those of a $100 Yagi by more than the price difference suggests.
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“My SWR is 1.0:1 across the band, so my Yagi is perfect” — possibly, but more often the matching network is absorbing the mismatch (e.g. a gamma capacitor heating up). Verify the gain with a known reference (compare against a dipole) — a flat SWR with low gain is the classic “matching network ate the signal” failure.
17. Resources
- Yagi & Uda 1926 original paper (translated; Tohoku Imperial University) — the foundational publication.
- ARRL Antenna Book Ch. 11 (Yagi-Uda arrays) — the canonical amateur Yagi reference.
- DL6WU Yagi designs (Günter Hoch DL6WU) — published 144 MHz / 432 MHz EME-grade designs.
- K1FO Yagi designs (Steve Powlishen K1FO) — variant of DL6WU with optimized side-lobe suppression.
- G0KSC LFA design documentation — the patent and original LFA papers from Justin Johnson.
- Innovantennas / DX Engineering Yagi white papers — modern commercial design notes.
- L. B. Cebik (W4RNL) papers on Yagi modeling — the deepest treatment of NEC-modeled Yagi optimization.
- M2 Antennas catalog and design documents — commercial reference.
- Schmidt + Stuart “Optimized Yagi-Uda Antennas” — older but classic optimization reference.
- 4nec2 / EZNEC / MMANA-GAL software (Vol 28) — the modeling tools that turn theoretical Yagi designs into buildable plans.