Build a Bruce Array
The Bruce array is a clever piece of 1930s antenna engineering: a single wire, folded back and forth in a zigzag, creates several in-phase half-wave radiating sections without needing any separate phasing stubs or crossed feeders. The short vertical jumper sections between the radiating bays are folded close enough together that their fields cancel, leaving just the horizontal half-wave sections to do the radiating — all fed from one wire, one connection. This guide covers the complete build from bay dimensions through feedpoint assembly and tuning.
Each Bay Is a Half-Wave Radiator
The Bruce array's horizontal sections ("bays") are each a half-wave length of wire, exactly like a dipole element. Every bay carries current in the same direction at the same time, so their radiation reinforces broadside to the array, the same collinear principle behind the Lazy H's rows — but here achieved without any separate open-wire phasing sections.
The Folded Jumper — Why It Doesn't Radiate
Between each pair of bays, the wire folds down and back up in a short vertical "U" — typically a small fraction of a wavelength, much shorter than the bays themselves. Because the two sides of this fold run so close together and carry current in opposite directions (down, then back up), their radiated fields effectively cancel at any meaningful distance. This is the same current-cancellation principle used in folded dipole matching sections, just applied here to link multiple bays without disturbing the phase relationship.
Gain vs. Bay Count
More bays generally means more gain, following the same broadside-collinear-array logic as any multi-element in-phase design — though with diminishing returns and rapidly increasing physical length as bays are added:
- 2 bays: modest gain over a single dipole, a good entry point for a first build.
- 4 bays: a common practical choice, meaningfully more gain, roughly double the span of the 2-bay version.
- 6 bays: further gain, but the array becomes quite long and mechanically demanding to support evenly.
Feedpoint and Matching
The Bruce array is typically fed at one end (at the first bay's outer end) or occasionally at the center, with an impedance that varies with bay count and doesn't land near a clean 50Ω. Feed with open-wire or ladder line into a balanced antenna tuner, matching the feed approach used by the other historical arrays on this site.
| Band | Bay length (ft) | Jumper drop at 0.075λ (ft) | Total span, 4 bays (ft) |
|---|---|---|---|
| 40m (7.15 MHz) | 65.5 ft | 10.3 ft | ~262 ft |
| 20m (14.15 MHz) | 33.1 ft | 5.2 ft | ~132 ft |
| 17m (18.1 MHz) | 25.9 ft | 4.1 ft | ~104 ft |
| 15m (21.2 MHz) | 22.1 ft | 3.5 ft | ~88 ft |
| 10m (28.4 MHz) | 16.5 ft | 2.6 ft | ~66 ft |
Bruce Array Calculator
Materials for a complete Bruce array
Building the Bruce Array
This build uses one continuous wire folded at each bay boundary — plan the entire layout on paper before cutting or bending anything.
Mark Out the Full Wire Length
Calculate the total wire needed: N bays at the half-wave bay length, plus (N-1) jumper drops counted twice each (down and back up). Mark these segments on your wire before making any folds.
Fold the First Jumper
At the end of the first bay, fold the wire down by the jumper-drop distance, then back up to start the second bay. Use a small standoff insulator or spreader to hold the two sides of the fold at a consistent, close spacing.
Repeat for Each Remaining Bay
Continue folding a jumper section at the end of each bay until all N bays are connected in one continuous zigzag run.
Attach End Insulators
Terminate both far ends of the completed zigzag with end insulators and support rope.
Establish the Feedpoint
Connect your feedline at one end of the array (the most common feed point) — strip and connect the open-wire or ladder line conductors to the wire end and to a nearby support point or counterpoise connection as your feed system calls for.
Raise the Array
Raise the entire zigzag run between your end supports (and any intermediate supports needed for a long, multi-bay array), keeping the bays roughly level and the jumper folds consistently oriented.
Tune and Verify
Connect the feedline to your balanced tuner and find a low-SWR setting at your target frequency.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| Gain seems much lower than expected for the bay count | Jumper folds spaced too widely, radiating instead of canceling | Check fold spacing against the 0.05-0.1λ guideline | Tighten the fold spacing at each jumper point |
| Tuner can't find a low SWR anywhere | A fold accidentally shorted, or feedpoint connection fault | Check continuity along the full wire run and at the feedpoint | Inspect each fold for accidental contact; re-solder the feedpoint |
| Pattern seems lopsided rather than symmetric bidirectional | Bay lengths not uniform, or uneven fold spacing along the run | Measure each bay individually against the target length | Re-measure and adjust any bay that's off from the others |
| Array sags badly in the middle | Insufficient intermediate support for a long multi-bay run | Sight along the array for excessive sag | Add an intermediate support point for arrays of 4+ bays |
| SWR shifts with weather | Feedline spacing affected by ice or wet conditions | Check feedline spacing after weather events | Use commercial ladder line with stable dielectric spacing |
How is this different from a Lazy H's collinear row?
A Lazy H connects its collinear elements with a separate open-wire phasing section running parallel to (but electrically distinct from) the radiating elements. The Bruce array instead folds the connecting wire directly into a tight vertical jumper as part of the same continuous piece of wire, avoiding the need for a separate phasing-line component.
How many bays should I build?
2 bays is a reasonable first build with a manageable span. 4 bays is a common practical choice for meaningfully more gain. Beyond 6 bays, the array becomes long enough that mechanical support and even bay lengths become the main challenge, not the electrical design.
Why doesn't the folded jumper section radiate?
The two sides of each fold carry current in opposite directions and are spaced close together, so their radiated fields largely cancel at any practical distance — the same current-cancellation principle that keeps a folded dipole's matching section from radiating significantly.
What's the historical background of this design?
The Bruce array dates to 1930s shortwave broadcast antenna engineering, valued for achieving multi-bay collinear gain from a single wire and minimal hardware — an efficient use of materials at a time when antenna construction resources were often limited.
Can I feed this array at the center instead of the end?
Yes, center feeding is used by some builders and changes the feedpoint impedance and current distribution somewhat, but end feeding (as covered in this guide) is the more commonly documented approach and simpler to build with a single feedline run.
Do I need a balun with this antenna?
As with the other historical wire arrays on this site, feeding with balanced open-wire line into a balanced tuner avoids needing a balun in that feed path; if you instead use coax and an unun, ensure good common-mode isolation.