Build a Quad Loop and Quad Beam Antenna
The cubical quad — commonly called simply the quad — is one of the most beloved HF beam antennas in amateur radio, combining genuine gain, wide bandwidth, low radiation angle, and an often-claimed advantage in signal-to-noise ratio compared to Yagi antennas at the same height. Built from full-wave wire loops supported on fibreglass or bamboo spreader arms, the quad is surprisingly lightweight for its performance, mountable on a modest rotator and mast, and buildable entirely from wire and off-the-shelf hardware. This guide covers the single-loop quad as a fixed or rotatable antenna, the 2-element quad beam with driven element and reflector, the 3-element quad with additional director, spreader arm construction, feedpoint impedance and matching, multi-band configurations, and practical installation for a permanent fixed-station quad beam.
The Full-Wave Loop — Starting Point for the Quad
A quad loop is a full-wave closed wire loop — one complete wavelength of wire formed into a square shape and fed at one corner or the midpoint of one side. This distinguishes it from a dipole (half-wave, open ends) and from a small transmitting loop (much less than a full wave). The full-wave loop has unique properties that make it the basis of the quad beam:
Adding Elements — From Loop to Beam
Like a Yagi, the quad beam uses parasitic elements to add gain and directivity. A reflector loop slightly larger than the driven element is placed behind it; a director loop slightly smaller is placed in front. The spacing and size of each element determines the gain and front-to-back ratio:
Quad vs Yagi — the Long-Running Debate
The comparison between quads and Yagis occupies more pages of amateur radio literature than almost any other antenna topic. The practical summary:
- Gain: equal-element quads and Yagis produce similar gain when the Yagi is optimised. A 3-element quad provides approximately the same gain as a 3-element Yagi of similar boom length.
- Bandwidth: quads are generally broader in SWR bandwidth than equivalent Yagis — a 2:1 SWR bandwidth of 200–400 kHz is typical for a 20m 2-element quad, versus 100–200 kHz for a 2-element Yagi.
- Low-angle radiation: the quad's full-wave loop carries current higher above ground than a half-wave Yagi element at the same mounting height — the quad's effective radiation centre is higher, which improves low-angle DX performance at a given mast height.
- Noise: many operators report better signal-to-noise ratios on the quad than on a Yagi of similar gain. This is difficult to quantify objectively but is widely reported.
- Construction: quads use wire and fibreglass spreaders — no aluminium element fabrication needed. Yagis use aluminium tubing but have no spreader arm fabrication. Quads are more wind-resistant due to lower wind loading; Yagis are more mechanically robust long-term.
- Best use case: the quad excels at modest heights (30–50 ft) on 20m and 15m where its higher effective radiation centre gives it an edge over a Yagi at the same physical height.
Multi-Band Quad Construction
One of the quad's greatest practical advantages is multi-band operation from a single physical structure. Multiple loops for different bands can share the same spreader arms, with each band's loop nested inside or alongside the next larger band's loop:
| Band | Driven perimeter | Driven side | Reflector perimeter | Director perimeter | Refl–DE spacing | DE–Dir spacing | Boom length (3-el) |
|---|---|---|---|---|---|---|---|
| 40m | 140.6 ft | 35.2 ft | 144.1 ft | 136.3 ft | 13.9 ft | 10.5 ft | 24.4 ft |
| 20m | 71.0 ft | 17.8 ft | 72.8 ft | 68.9 ft | 13.9 ft | 10.4 ft | 24.3 ft |
| 17m | 55.5 ft | 13.9 ft | 56.9 ft | 53.9 ft | 10.9 ft | 8.1 ft | 19.0 ft |
| 15m | 47.4 ft | 11.9 ft | 48.6 ft | 46.1 ft | 9.3 ft | 7.0 ft | 16.3 ft |
| 12m | 40.3 ft | 10.1 ft | 41.3 ft | 39.1 ft | 7.9 ft | 5.9 ft | 13.8 ft |
| 10m | 35.3 ft | 8.8 ft | 36.2 ft | 34.2 ft | 6.9 ft | 5.2 ft | 12.1 ft |
Materials for a 2-element 20m quad beam (driven element + reflector) on a 14-ft boom
Building the 2-Element 20m Quad Beam
This guide builds a 2-element 20m quad beam with corner-fed driven element and a parasitic reflector. The build sequence is: hub plates → boom assembly → spreader arms → driven element loop and feedpoint → reflector loop → balance point and mast bracket → raise and test. Build and test on the ground before raising permanently.
Fabricate the Hub Plates
Each hub plate holds four spreader arms at 90° intervals and attaches to the aluminium boom. For a 2-element quad, two hub plates are needed — one for the driven element and one for the reflector. The hub plate can be commercial (available from DX Engineering and other suppliers as part of quad kits) or fabricated from 1/8-inch aluminium plate:
Assemble the Boom and Attach Hub Plates
Cut the aluminium boom to 14 feet for a 2-element 20m quad (reflector-to-driven spacing of 13.9 ft plus allowance for hub plate thickness and overhang). Mark the boom at the reflector position (at one end) and at the driven element position (13.9 ft toward the other end). Attach the hub plates at each marked position using U-bolts.
Identify the balance point of the completed boom — for a 2-element quad, the balance point is approximately at the driven element position or slightly forward of it. Mark this point — the mast-to-boom bracket mounts here. An unbalanced boom requires counterweighting or acceptance of non-level rotation — always find the balance point before cutting the boom to final length.
Install Spreader Arms
Insert the four fibreglass spreader arms into each hub plate — two pointing horizontally (left and right) and two vertically (up and down). Each arm should extend 10 feet from the hub centre — the 20m loop corner attachment point is at the 8.9-ft mark on each arm (half the loop side length of 17.8 ft = 8.9 ft from centre). Mark each arm at this point with tape or a permanent marker.
Secure each spreader arm with a hose clamp tightened on the arm just inside the hub plate. Do not overtighten — fibreglass tubing cracks if a hose clamp is applied with excessive force. Snug plus one quarter turn is adequate. For additional security, drill a 3/16-inch hole through both the hub plate and the fibreglass arm and insert a stainless steel bolt — this prevents the arm from pulling out under wire tension.
Cut and Attach the Driven Element Loop Wire
Cut the driven element wire to 72 feet — 71.0 ft nominal perimeter plus 1 foot extra for the feedpoint gap and overlap. Starting at the bottom corner of the driven element hub (bottom spreader arm tip), attach the wire at the tip insulator and run the wire to the next arm tip (left or right), continuing around all four corners until the wire returns to the starting point. Leave a 4-inch gap at the bottom corner for the feedpoint — the two wire ends at this gap are the feedpoint terminals:
Install the Feedpoint Balun and Matching
A corner-fed quad loop presents approximately 100–120 Ω at the feedpoint. A 2:1 impedance transformer (balun) steps this down to 50–60 Ω for the coax feedline. Several matching approaches are used in practice:
Attach the Reflector Loop Wire
The reflector is a closed loop with no feedpoint gap — the wire is continuous around all four corners with no break. Cut the reflector wire to 74 feet (72.8 ft nominal plus allowance) and attach it to the reflector hub's spreader arm tips using the same technique as the driven element. Join the two wire ends with a small solder splice or crimp connector — the reflector is a closed loop with no external connections:
Mount on Mast, Raise, and Verify
Attach the mast-to-boom bracket at the pre-determined balance point. Mount the quad on the mast and rotator system. A 2-element 20m quad weighs approximately 8–12 lbs including wire — any medium-duty rotator handles this load comfortably. Raise the antenna to operating height and perform a final NanoVNA sweep from 13–15 MHz:
Single Quad Loop — Fixed Station or Rotatable
A single full-wave quad loop — without parasitic elements — is a worthwhile antenna in its own right, providing 1–2 dBd gain over a dipole and a lower radiation angle. It is simpler to build than a beam (one element, four spreader arms, no boom) and can be installed as a fixed broad-coverage antenna or rotated on a light-duty mast:
- Fixed installation: mount the loop on four fibreglass spreader arms from a fixed post or tree. Orient the loop face toward the primary DX direction. A fixed single quad loop on 20m pointing toward Europe from North America gives broad coverage of the European continent without rotation.
- Wire support alternative: the single quad loop can also be supported by four ropes from a central mast top — no fibreglass spreaders needed. The wire itself forms the square shape under tension from the rope corners. This is the simplest possible quad installation.
- Feedpoint for single loop: corner feed gives horizontal polarisation at ~100 Ω; use a 2:1 balun. Side-centre feed gives vertical polarisation at ~50 Ω; direct coax connection with a 1:1 choke balun.
- Bandwidth: a single quad loop on 20m covers the entire 20m amateur band within 2:1 SWR from a single resonant feedpoint — one of the broadest wire antennas for a single band.
- Multi-band single loop: with an ATU, a quad loop cut for one band works on higher bands. A 20m quad loop works well on 10m (2× frequency) and somewhat on 15m. For guaranteed multi-band coverage, a doublet is more reliable.
3-Element Quad Beam — Adding a Director
Adding a director element in front of the 2-element quad increases gain by approximately 3 dB and improves front-to-back ratio. The 3-element quad on 20m achieves approximately 7 dBd gain — competitive with a 3-element Yagi on the same boom length:
- Director dimensions: the director loop perimeter is 975/f(MHz) — approximately 3% shorter than the driven element. For 20m: 975/14.15 = 68.9 ft perimeter, or 17.2 ft per side.
- Director spacing: 0.15–0.20λ in front of the driven element. For 20m: 10.4–13.9 ft in front of the driven element.
- Director is a closed loop: like the reflector, the director has no feedpoint gap — it is a closed continuous wire loop.
- Boom length: a 3-element 20m quad requires a boom of approximately 24 ft (reflector to director) — a significant structure that requires a medium-duty rotator and robust mast.
- Weight: a 3-element 20m quad weighs approximately 15–25 lbs including hardware — similar to a commercial 3-element Yagi and suitable for a Ham-IV or equivalent rotator.
- Director tuning: director length is less sensitive to exact tuning than reflector length. The theoretical dimension works well as a starting point; fine-tune for maximum forward gain by shortening in 2-inch increments while monitoring a known signal from the front direction.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| High SWR across entire 20m band — no minimum visible | Open circuit in driven element loop or feedpoint balun failure | Check continuity around full driven element loop; check balun terminal connections to wire ends | Repair wire break at spreader arm tip or hub connection; replace failed balun; verify coax connections at balun |
| SWR minimum shifted 200–400 kHz above or below target | Driven element loop wire length incorrect | Measure actual loop perimeter with tape measure; compare to 1005/f formula result | Add wire to loop if resonance too high; trim wire if too low; adjust in 6-inch increments |
| Good SWR but poor front-to-back ratio — antenna seems bidirectional | Reflector wire length not optimised; or reflector is an open loop (gap at wrong place) | Verify reflector is a closed continuous loop; check reflector perimeter length vs 1030/f formula | Ensure reflector has no gap; add 3–6 inches to reflector wire and recheck F/B; use signal from behind antenna to optimise |
| Spreader arm deflecting excessively under wire tension | Wire tensioned too tight; or fibreglass tubing too thin-walled for the arm length | Measure deflection at arm tip — over 6 inches is excessive for a 10-ft arm | Reduce wire tension by loosening tip attachments slightly; replace under-rated arms with thicker-walled fibreglass tube; add diagonal support cord from hub to arm tip |
| SWR varies significantly with rotation angle | Nearby metal object coupling into antenna at specific angles; or unbalanced feedline causing rotation-dependent SWR | Note specific bearings where SWR is high — consistent with nearby metal object direction | Identify and remove or relocate nearby metal within 1 wavelength; ensure coax runs down the centre of the boom without lateral runs that couple into the antenna |
| Wire breaks at spreader arm tip after several months | Mechanical fatigue from wind-induced movement at the tip attachment point; or UV degradation of wire insulation at sharp bend | Inspect all tip attachment points for cracking or fraying | Use stainless steel thimbles at tip attachment points to reduce sharp bends; use bare copper wire at tips (no insulation to crack); add short strain-relief loops at each tip |
| Gain noticeably reduced after heavy rain or ice event | Wire sag from ice loading changed element geometry; or water in balun enclosure | Inspect all loop wires for sag or deformation; check balun for moisture ingress | Re-tension sagging wire sections; re-seal balun enclosure; add drip loop to coax at feedpoint |
Is a quad beam really better than a Yagi?
At the same boom length and element count, a quad and a Yagi produce nearly identical gain when both are optimised. The quad's practical advantages are broader SWR bandwidth (the entire 20m band within 2:1 SWR from a properly built 2-element quad) and a higher effective radiation centre at a given mast height — the quad's loops extend both above and below the boom, raising the average current height compared to a Yagi element at boom height. At modest mounting heights (30–50 ft), this height advantage gives the quad a measurable DX advantage. The Yagi's advantages are mechanical robustness and simpler element tuning. Both are excellent antennas — the choice often comes down to construction preference and mounting constraints.
Can I build a multi-band quad on a single set of spreader arms?
Yes — this is one of the quad's great strengths. Multiple loops for different bands share the same four spreader arms, with each band's loop attached at different distances from the hub centre. The 20m loop corners attach at the arm tips; the 10m loop corners attach at half that distance from the hub. Each band requires its own driven element wire with its own feedpoint and balun, and its own coax run down the boom. The reflectors for each band are separate closed loops also on the same arms. A 5-band (20m, 17m, 15m, 12m, 10m) quad on one set of 12-ft spreader arms is a practical and popular configuration.
What is the best spreader arm material?
Fibreglass tube (pultruded fibreglass rod or tube) is the universally preferred material for quad spreader arms. It is non-conductive (essential — conductive arms couple into the loop wire and detune the antenna), strong, lightweight, UV-resistant with the right formulation, and available in many sizes. One-inch OD fibreglass tube with 0.125-inch wall thickness handles 10-ft arm spans on 20m and 15m comfortably. Bamboo is a traditional alternative — lighter than fibreglass and free if you can source it — but less durable and susceptible to cracking after several years of weathering. Avoid aluminium, steel, or any conductive material for spreader arms.
How do I orient the quad for horizontal vs vertical polarisation?
The polarisation of a quad beam is determined by how the driven element is fed and oriented. For horizontal polarisation (most common for HF DX), the loop is mounted as a diamond (corners at top, bottom, left, right) and fed at the bottom corner. For vertical polarisation, the loop is also mounted as a diamond but fed at the midpoint of one of the sides (not a corner). Alternatively, rotating the whole loop 45° so the flat sides face up and down also changes the polarisation characteristics. For standard HF DX work, horizontal polarisation is conventional — it matches the polarisation of most DX contacts and of other fixed beam stations.
Can I build a quad beam for 40m?
Yes, but the dimensions are demanding — a 2-element 40m quad has 35-ft sides on each loop element, requiring 14-ft spreader arms and a 14-ft boom. The complete structure stands approximately 70 ft tall (loop height plus mast) and weighs 25–40 lbs. This is a serious antenna project requiring a substantial tower and heavy-duty rotator. Many operators build a 40m quad as a fixed antenna (no rotation) pointed toward the primary DX direction, which eliminates the rotator requirement and allows a lighter support structure. A fixed 2-element 40m quad pointed northeast from North America is a formidable DX antenna on the 40m band.
Does the quad need a ground plane or radials?
No — the quad is a balanced, elevated antenna that operates entirely independently of the ground. No radials, no ground system, and no connection to earth is needed or useful. The feedpoint balun isolates the coax from the antenna's balanced feed system, and the antenna's performance is entirely determined by its wire geometry and height above ground. This is a significant practical advantage over vertical antennas — the quad's performance does not depend on soil conductivity, and it works equally well over any type of ground including concrete, rock, or salt water.