Build a 3-Element Yagi Antenna
The 3-element Yagi is the most widely built directional HF antenna in amateur radio — the benchmark against which all other beam antennas are measured. Adding a director element in front of the driven element raises forward gain to 6–8 dBd and front-to-back ratio to 20–25 dB, while the beta match feed system provides a clean, no-adjustment 50 Ω feed without moving parts. A 20m 3-element Yagi on a 24-foot boom is the standard mid-sized tower antenna that transforms contest and DX operating for thousands of operators every year. This guide covers the complete design, element sizing, tapered element construction, boom assembly, beta match wiring, and the step-by-step tuning procedure for a high-performance 20m 3-element Yagi.
Director, Driven Element, and Reflector
The 3-element Yagi adds a director element in front of the driven element. The director is shorter than the driven element and its re-radiated signal adds constructively in the forward direction — working in concert with the reflector behind to produce significantly more gain and better front-to-back than the 2-element design:
W3LPL / Classic 3-Element Design Dimensions
This guide uses the well-proven classic 3-element Yagi proportions that have been replicated successfully by thousands of builders. These dimensions are derived from W6SAI and subsequent NEC modeling and represent a practical optimum for a homebuilt 3-element Yagi on a 24-foot boom:
The Beta (Hairpin) Match
The beta match is the preferred feed system for a 3-element Yagi — it is fixed (no adjustable components), balanced, and easily built from a short length of wire or rod. It transforms the low feedpoint impedance (22–28 Ω) to 50 Ω using a shorted transmission line stub placed across the feedpoint:
3-Element vs 2-Element — The Real-World Difference
The improvement of a 3-element over a 2-element Yagi is significant and operationally meaningful in every aspect of performance:
| Band | Freq (MHz) | Director | Driven element | Reflector | DE–DIR spacing | DE–REF spacing | Boom |
|---|---|---|---|---|---|---|---|
| 10m | 28.40 | 15.8 ft | 16.4 ft | 17.3 ft | 6.1 ft | 6.9 ft | 13.0 ft |
| 15m | 21.20 | 21.1 ft | 21.9 ft | 23.2 ft | 8.1 ft | 9.3 ft | 17.4 ft |
| 17m | 18.10 | 24.7 ft | 25.7 ft | 27.2 ft | 9.5 ft | 10.9 ft | 20.4 ft |
| 20m | 14.15 | 31.6 ft | 32.9 ft | 34.8 ft | 12.2 ft | 13.9 ft | 26.1 ft |
| 40m | 7.150 | 62.8 ft | 65.4 ft | 69.0 ft | 24.3 ft | 27.5 ft | 51.8 ft |
Yagi 3 Element Calculator
This design has published dimensions for more than one band. The default shown below is the first/most common one on the page -- change the frequency and recalculate for the other bands.
Materials for a 20m 3-element Yagi with beta match, covering 14.0–14.35 MHz
Why the Beta Match Suits the 3-Element Yagi
The beta match (also called the hairpin match) is the preferred feed system for 3-element Yagi designs for several compelling reasons that make it superior to the gamma match used on the 2-element version:
- No moving parts: the beta match is a fixed-length wire stub — once set correctly during construction, it requires no further adjustment and cannot drift or corrode like a variable capacitor.
- Balanced feed: the beta match feeds the split driven element symmetrically from both halves simultaneously, producing a balanced pattern with no asymmetry from an off-center feed connection.
- Low loss: the stub is a short section of transmission line with near-zero resistive loss — it adds essentially nothing to the antenna system losses.
- Easy verification: a correctly built beta match produces a predictable SWR curve — a clean, symmetric dip centered on the design frequency. Deviations from this pattern indicate specific, diagnosable construction errors.
- No weatherproofing of moving parts: the only weatherproofing needed is for the coax connections and the feedpoint enclosure — the stub wire itself is simply bare wire in open air.
Beta Match Dimensions and Construction
The beta match is a U-shaped wire bridge connecting the two halves of the split driven element. The driven element is deliberately cut 2–4% shorter than resonance, making it capacitively reactive. The hairpin stub adds inductive reactance to cancel this capacitance and simultaneously transforms the impedance:
Building the 20m 3-Element Yagi
Build all three elements and the boom on the ground. Verify element lengths with the NanoVNA before assembly. Mount elements to boom. Build and install the beta match at the feedpoint. Raise to operating height and verify SWR. The beta match requires no adjustment at height if constructed correctly on the ground.
Cut and Prepare the Boom
Cut the 2-inch OD aluminum tubing to 26 feet for the boom. If a single 26-foot length is not available, join two sections with an internal sleeve coupler — a 12-inch length of 1.75-inch OD aluminum tubing inserted into both boom sections at the joint, secured with two bolts through all layers. Mark the three element positions:
Build All Three Elements
Build all three elements using the same tapered construction as the 2-element guide — 1.25-inch OD center section telescoping into 1.0-inch OD outer sections. Starting lengths for each element (cut long, trim to final during tuning):
Verify Individual Element Resonance
Before mounting to the boom, verify each element's resonance individually using the NanoVNA. Connect the NanoVNA to the center of each element (temporarily bridging the driven element halves with a short jumper) and sweep 12–16 MHz. This verifies the element lengths are within specification before assembly:
Mount All Three Elements to the Boom
Mount all three elements to the boom in sequence — director first, then driven element, then reflector. Verify correct orientation after each mounting: all elements must be parallel to each other and perpendicular to the boom. Any twist in element plane relative to the boom shifts the polarization and degrades the pattern.
For the driven element, install the HDPE insulator plates between the element saddles and the boom surface. The 2-inch feedpoint gap at the driven element center must be maintained — the two halves should be exactly 2 inches apart at the boom crossing, not touching or bridged by any metal hardware.
Build the Beta Match Feedpoint Assembly
Construct the beta match and feedpoint enclosure on the ground before raising. The feedpoint assembly consists of: the hairpin stub wire, the coax connection hardware, the current choke, and the weatherproof enclosure — all pre-assembled and ready to connect to the driven element halves:
House the entire assembly in the weatherproof enclosure. Mount the enclosure to the boom at the driven element center position, with the hairpin stub extending upward (or to either side) from the feedpoint gap. The stub can also extend downward — the orientation relative to vertical does not affect electrical performance.
Ground-Level SWR Check Before Raising
With the antenna assembled horizontally at ground level, connect the NanoVNA and sweep 13–16 MHz. The antenna at ground level will not show the correct operating SWR (ground proximity changes the apparent impedance significantly), but it should show a resonance dip somewhere in the 13–16 MHz range. This confirms the feedpoint assembly is connected correctly and the beta match is functioning before the antenna goes to height.
Raise to Operating Height and Measure SWR
Raise the antenna to its operating height and connect the NanoVNA at the shack end of the feedline. Sweep 13.5–15.5 MHz. With a correctly built beta match, the SWR minimum should be near 14.150 MHz and below 2:1 without any adjustment:
Adjust Beta Stub Length for Perfect Match
If the SWR minimum needs adjustment, modify the hairpin stub length. This is done at the installed height — the stub is accessible at the feedpoint enclosure on the boom. Carry a pair of wire cutters, wire, and a small soldering iron (or Scotchlock connectors) for field modification of the stub length:
- To raise the SWR minimum frequency (shift resonance upward): shorten the stub by cutting 1 inch from the shorted end. Re-measure. Repeat in 1-inch steps.
- To lower the SWR minimum frequency (shift resonance downward): add wire to the shorted end of the stub, extending it by 1–2 inches. A short pigtail soldered or clamped to the shorted bridge accomplishes this without desoldering.
- If SWR minimum is correct but minimum SWR is above 2:1: the stub spacing (separation between the two wire legs) needs adjustment. Wider spacing lowers the minimum SWR; narrower spacing raises it. Adjust in 0.5-inch increments.
Verify Pattern and Document
Once SWR is confirmed, verify the antenna's directional pattern on-air. Point the antenna at a known distant signal (a DX beacon, a cooperative station, or any consistent signal source at a known direction). Record the S-meter reading, rotate 180°, and record again. A well-built 3-element Yagi should show 20–25 dB (3–4 S-unit) front-to-back difference. Also note the 3 dB beamwidth by rotating slowly through the forward lobe and identifying the bearings where the signal drops by one S-unit — these two bearings should be approximately 65–75° apart.
Document and weatherproof: record all element final lengths, beta stub dimensions (length, wire spacing), SWR at resonance and at band edges, front-to-back measurement, and antenna height. Weatherproof the feedpoint enclosure with self-amalgamating tape over all coax connections. Apply RTV sealant around all cable entries into the enclosure. Apply Noalox at any exposed aluminum-to-aluminum contact points and re-tighten all hardware after the first season.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| No SWR dip in 13–16 MHz sweep | Driven element halves not connected to beta stub legs, or DE shorted to boom | Check DC resistance from coax center to shield — should be short circuit (through stub) not open | Verify stub wire legs connect to each DE half; verify HDPE insulators are present between DE and boom |
| SWR minimum visible but above 3:1 at operating height | Beta stub spacing too narrow for the feedpoint impedance | With NanoVNA, note the exact minimum SWR — if it is 2.5–3.5:1, stub spacing is likely the issue | Spread the two stub wire legs apart by 1 inch; re-measure; repeat until minimum SWR is below 1.5:1 |
| SWR correct on 20m but no front-to-back pattern | Antenna pointing backward or director and reflector swapped | Rotate 180° — if signal gets stronger, antenna is pointed backward | Rotate antenna 180° on mast; director end must point toward the target |
| Front-to-back ratio only 10–12 dB instead of 20+ dB | Reflector too short or wrong element spacing | Measure reflector length — should be ~34.8 ft for 14.150 MHz design | Extend reflector outer sections to correct length; verify reflector-to-DE spacing is within 6 inches of 13.9 ft |
| SWR rises significantly after rain | Water ingress into feedpoint enclosure reaching coax connections | Wipe feedpoint dry and re-measure — improvement confirms water ingress | Open, dry, and reseal enclosure; add desiccant pack; improve waterproofing of all cable entry points |
| SWR drifts over seasons — needs re-tuning each year | Corrosion at element joints changing electrical length | Inspect all hose clamp joints for green oxide; check lock bolts for tightness | Disassemble joints, clean with wire brush, re-apply Noalox, reassemble and retighten all hose clamps |
| Resonance shifts after strong wind event | Element sections slipped in hose clamp joints | Measure all element lengths — compare to documented final lengths | Re-extend slipped sections to original position; install additional lock bolts through each overlap; re-tighten all clamps |
How does a homebrew 3-element Yagi compare to a commercial one?
A carefully built homebrew 3-element Yagi using the dimensions in this guide matches commercial antennas in electrical performance — the physics are the same and aluminum is aluminum regardless of who bends it. The differences between homebrew and commercial antennas are in mechanical reliability (commercial antennas use more refined element-to-boom hardware and have been wind-tunnel tested), aesthetic finish, and warranty coverage. Electrically, a homebrew Yagi with correctly cut elements, properly insulated driven element, correctly built beta match, and proper current choke will produce identical forward gain, front-to-back ratio, and bandwidth to a commercial antenna with the same dimensions. Many experienced operators prefer homebrew Yagis precisely because they understand every component and can repair or modify the antenna in the field.
Should I optimize for maximum gain or maximum front-to-back ratio?
This is a genuine trade-off, and the answer depends on your primary operating style. Optimizing for maximum gain (slightly different spacings and element lengths) produces about 0.5–1 dB more forward signal but reduces front-to-back ratio from 25 dB to 15–18 dB. Optimizing for maximum front-to-back (the dimensions in this guide) produces slightly less forward gain but provides the best interference rejection from the rear. For DX contesting where minimizing QRM from behind is crucial, maximum front-to-back is the priority. For long-haul DX on quiet bands, maximum gain is marginally preferable. The dimensions in this guide are the classical compromise that most builders find ideal for general-purpose use.
What wind survival rating should I design for?
The design wind survival target depends on your location. For most continental US locations, designing for 80–100 mph wind survival is appropriate. The 2-inch OD boom handles 26 feet with modest sag but is adequate mechanically for these wind speeds when properly supported at the mast. The element tips are the most vulnerable points — 1-inch OD outer sections at the element tips (approximately 10 feet long) can flex significantly in high winds. Adding a guy wire truss from a central boom point to the element tips, or adding internal support rods inside the hollow tubing at the tips, provides additional wind resistance if you are in a high-wind area. In coastal or mountain locations where sustained 100+ mph winds occur, consult a structural engineer or use a proven commercial antenna design for the specific wind loading expected.
How do I weatherproof the beta match hairpin stub?
The bare wire hairpin stub does not need weatherproofing — it is exposed wire in free air and the aluminum or copper wire handles the outdoor environment without protection. Light oxidation on the stub wire does not significantly affect its performance since the stub handles only voltage (not high current) and its resistance is negligible. What does need weatherproofing is the feedpoint enclosure housing the coax connections, the SO-239, and the wire-to-element connections where the stub legs meet the element halves. These connection points should be coated with self-amalgamating tape and RTV sealant. The coax run from the feedpoint down the boom to the mast should be secured with UV-resistant cable ties and the PL-259/SO-239 connection should be wrapped in self-amalgamating tape.
Can I use a 1:1 balun instead of the beta match?
A 1:1 current balun does not match the impedance — it only provides common-mode rejection. The 3-element Yagi with these spacings presents approximately 25 Ω at the feedpoint, not 50 Ω. Connecting a 50 Ω coax directly with a 1:1 balun gives 2:1 SWR — usable with the radio's internal ATU but not ideal for a fixed installation. A better alternative if avoiding the beta match: use a folded dipole driven element, which multiplies the feedpoint impedance by approximately 4× (25 Ω × 4 = 100 Ω), then use a 2:1 balun to match 100 Ω to 50 Ω. This approach is mechanically simpler than the beta match and provides a balanced feed without adjustment. The folded dipole driven element is slightly wider in bandwidth than a split dipole, which is an additional advantage.
What rotator do I need for a 20m 3-element Yagi?
The wind loading of a 20m 3-element Yagi is typically 8–12 square feet, depending on element diameter and boom width. A rotator rated for this wind area and boom moment is required — the Yaesu G-400, G-450, M2 OR2800, and similar mid-class rotators handle this antenna well. The lighter CDE/Hy-Gain TR-44 and similar small rotators are marginal for a 26-foot boom antenna and may slip or fail in high winds. For a permanent installation in a windy location, size up to a Yaesu G-800 or equivalent. Install a thrust bearing above the rotator to reduce side-loading on the rotator shaft — the thrust bearing carries the antenna weight and most of the wind torque load, preserving the rotator for azimuth turning only. This significantly extends rotator life on a heavy antenna like the 3-element 20m Yagi.