Build a Delta Loop Beam Antenna for HF
Two full-wave delta loops spaced a quarter wavelength apart and fed with a 90° phasing harness produce a compact directional beam with genuine gain over a dipole and a pattern that favours low-angle DX radiation. The delta loop beam needs only one tall central support plus two low anchor points per element — making it one of the most practically achievable directional HF antennas for the home station with a single tall tree or mast.
What This Guide Covers
A single full-wave delta loop is an excellent antenna in its own right — it provides approximately 1–2 dBd gain over a dipole (depending on orientation and feed point position), offers multi-band operation with an ATU, and requires only one high support. This guide covers two configurations: first the single delta loop with its feed point options, then the two-element phased delta loop beam which adds a second loop spaced λ/4 behind the first and fed 90° out of phase to create a cardioid directional pattern with 4–5 dBd forward gain and useful front-to-back ratio.
Single Delta Loop
Full-wave loop with apex at the top. Feed at the bottom corner for horizontal polarisation and lower take-off angle, or at the midpoint of one side for vertical polarisation and lower radiation angle over good ground. Gain 1.1 dBd (H-pol) or 1.5 dBi over a dipole in free space.
Two-Element Phased Beam
Two loops spaced λ/4 apart, the rear element fed 90° late via a phasing line. Produces a cardioid pattern with 4–5 dBd forward gain and 10–15 dB front-to-back ratio. Can be switched between two directions by reversing the phasing cable connections.
Reversible Beam
By adding a coax relay at the phasing harness junction, the beam can be electrically switched between two opposite directions (e.g. Europe and USA from a UK station) without physically moving the antenna. A simple DC switch in the shack controls the relay.
Delta Loop Theory
A delta loop is a closed-wire antenna with a total circumference of one full wavelength at the operating frequency. The shape is an equilateral or isoceles triangle — two wire sides meeting at an apex at the top, and a horizontal base wire at the bottom. The triangular shape allows the loop to be supported from a single high point (the apex) with the two base corners anchored near ground level, making it mechanically convenient when only one tall support is available.
The feed point position on the loop determines the antenna's polarisation and radiation pattern.
Bottom Corner Feed — Horizontal Polarisation
Feeding the loop at one of the bottom corners produces predominantly horizontal polarisation. The radiation pattern is broadside to the plane of the triangle, with a figure-8 pattern in the horizontal plane. The take-off angle is moderate — lower than a low dipole but higher than a vertical. Feed point impedance at resonance is approximately 100–130 Ω, requiring a 2:1 balun for direct 50 Ω coax connection, or a short section of 75 Ω coax acting as an impedance transformer.
Side Midpoint Feed — Vertical Polarisation
Feeding the loop at the midpoint of one sloping side produces a mix of vertical and horizontal polarisation components, with the vertical component dominating. The radiation pattern shifts to favour lower elevation angles — useful for DX — and the feed point impedance is approximately 50–75 Ω, often allowing direct coax connection with a 1:1 choke balun. This is the recommended feed point for single-band DX use and for the phased beam configuration.
| Band | Frequency (MHz) | Total wire (m) | Side length (m) | Apex height (m) | Base width (m) |
|---|---|---|---|---|---|
| 40 m | 7.150 | 42.8 | 14.26 | 12.35 | 14.26 |
| 30 m | 10.125 | 30.2 | 10.07 | 8.72 | 10.07 |
| 20 m | 14.175 | 21.6 | 7.19 | 6.23 | 7.19 |
| 17 m | 18.118 | 16.9 | 5.63 | 4.87 | 5.63 |
| 15 m | 21.225 | 14.4 | 4.81 | 4.16 | 4.81 |
| 12 m | 24.940 | 12.3 | 4.09 | 3.54 | 4.09 |
| 10 m | 28.500 | 10.7 | 3.58 | 3.10 | 3.58 |
For a phased two-element beam: the element spacing is λ/4. At 14.175 MHz this is 300/(4×14.175) = 5.29 m. At 7.150 MHz it is 10.49 m. The two loops are set up side by side (both in the same vertical plane), with the rear loop spaced λ/4 behind the front loop in the desired beam direction.
Delta Loop Beam Calculator
Materials for a 20m two-element delta loop beam
Building the Single Delta Loop
Build and verify the first loop before adding the second element for the phased beam. Allow 5–8 hours for the complete two-element build.
Calculate and cut the wire to length
For 14.175 MHz, total wire = 306/14.175 × 0.97 = 20.94 m. Cut a single length of insulated copper wire to this measurement. Mark the two-thirds point from one end (13.96 m from the start) — this is where the apex will be located. Mark the midpoints of each of the two sloping sides at 6.98 m and 20.94 m from the start — these are the side midpoint feed point options.
Install the apex support
The apex of the delta loop sits at the top of the highest available support — a tree branch, mast, or purpose-built fibreglass pole. For 20 m, the apex needs to be at least 6.2 m high; for 40 m, at least 12.4 m. Tie a halyard rope to the apex insulator and hoist it to the support point. The insulator is a simple egg insulator — one side ties to the support rope, the other connects to the apex of the wire loop.
Route and tension the two sloping sides
From the apex insulator, run the wire down each sloping side to the two base corner insulators. The base corners should be anchored at ground level — garden stakes, fence posts, or existing ground anchors work well. Space the base corners so that the base of the triangle equals the side length (7.19 m for 20 m, making an equilateral triangle). The bottom of the loop should be at least 1–2 m above ground — low ground proximity detunes the loop and increases ground losses.
Connect the feed point
For the side midpoint feed (recommended), locate the midpoint of one sloping side (3.59 m from either the apex insulator or the base corner insulator along that side). Cut the wire at this point and install a feed point insulator. Connect the coaxial cable: inner conductor to one wire half, outer braid to the other. Install a 1:1 current balun immediately at the feed point. The coax then runs down the sloping side to the base and along the ground to the shack. The remaining base wire section (across the bottom) and the other sloping side complete the full-wave loop.
Initial SWR check
Connect an antenna analyser at the shack end of the feedline (or at the feed point with a short coax). Sweep across the target band. A correctly built 20 m side-fed delta loop should show SWR below 2:1 from 14.000 to 14.350 MHz, with minimum SWR of 1.2–1.6:1 somewhere in the band. If the minimum SWR is well above 2:1, check the loop circumference — the most common error is a total wire length that is significantly off from the calculated value. Trim from the base wire to shorten, or add a short extension to lengthen.
Install the second loop at λ/4 spacing
Once the first delta loop is working correctly, adding a second loop to create a directional beam is straightforward. At 14.175 MHz, λ/4 = 5.29 m. Place the second loop's apex and base corners exactly 5.29 m behind the first loop in the intended forward direction. All dimensions of the second loop are identical to the first. The second loop's feed point is at the same position on its structure (side midpoint) as the first loop's feed point.
Cut the phasing line precisely
The phasing line is a λ/4 section of 50 Ω coaxial cable that connects the two feed points and introduces exactly 90° of phase delay to the rear element. Using RG-213 with VF = 0.659: phasing length = λ/4 × VF = (300/(4×14.175)) × 0.659 = 5.29 × 0.659 = 3.49 m. Cut this length carefully — a 50 mm error at 14 MHz introduces several degrees of phase error that degrades the F/B ratio. Measure from the centre of one PL-259 connector to the centre of the other.
Wire the phasing harness
Use a T-connector or junction box at a central point between the two loops. From this junction: run equal lengths of coax to each loop's feed point. The front loop connects directly (0° phase). The rear loop connects through the λ/4 phasing line then onward to its feed point (−90° phase). The main feedline runs from the junction to the shack. All coax runs to the individual loop feed points should be of equal electrical length — if physical lengths differ, cut a matching section from a piece of the same coax to equalise them.
Test beam direction and F/B ratio
With the phasing harness connected, compare received signal levels from a known station in the forward direction versus a station approximately 180° behind the antenna. The forward signal should be 10–15 dB stronger than the reverse signal. If both directions sound equally strong, the phasing line length may be incorrect or the loop feed points are not at matched positions. If the beam points in the opposite direction to expected, simply swap the connections of the phasing cable at the junction — reversing which loop gets the phasing line reverses the beam direction.
Optional: install a remote switching relay
For a fully switchable two-direction beam, install a DPDT or SPDT coax relay at the phasing junction. In position A, the phasing line feeds the rear loop (beam points forward). In position B, the phasing line feeds the front loop (beam reverses). A simple 12 V DC supply and a toggle switch in the shack controls the relay. This allows instant beam reversal to work DX on opposite sides of the globe without physically moving anything.
Operating a Single Loop on Multiple Bands
One of the delta loop's most practical advantages is its ability to operate on multiple bands with an ATU. A 40 m delta loop (total circumference 42.8 m) resonates on 40 m as a full-wave loop, on 20 m as a two-wavelength loop, on 15 m as a three-wavelength loop, and so on at each harmonic. With an ATU and an open-wire feeder (ladder line into the ATU) rather than coax, the loop can be used on all HF bands from 40 m upward with acceptable efficiency.
The pattern changes at each harmonic — a 40 m loop on 20 m (where it is 2λ electrically) has a more complex multi-lobe pattern with higher peak gain than the fundamental. Running the same loop on 15 m (3λ) produces a narrow multi-lobe pattern with even higher peak gain in specific directions, useful when those lobes happen to align with desired DX paths.
40m loop on all bands: feed a 40 m delta loop with 450 Ω ladder line into a manual balanced ATU. This provides effective operation on 40, 30, 20, 17, 15, 12, and 10 m from a single antenna — a practical multi-band solution with only one set of supports and one feedline run.
| Configuration | Forward gain | F/B ratio | Feed Z | Supports needed |
|---|---|---|---|---|
| Single loop, bottom corner feed | 1.1 dBd H-pol | None (omnidirectional) | ~120 Ω | 1 apex + 2 base |
| Single loop, side midpoint feed | 1.5 dBd mixed pol | None (omnidirectional) | ~50–75 Ω | 1 apex + 2 base |
| Two-element phased beam | 4–5 dBd | 10–15 dB | ~50 Ω | 1 apex + 4 base |
| Moxon rectangle (comparison) | 5.5 dBd | 30–35 dB | 50 Ω direct | 1 hub + 4 corners |
| 3-element Yagi (comparison) | 7.5 dBd | 20–25 dB | 25 Ω + match | Mast + rotator |
How does the delta loop compare to a dipole at the same height?
A delta loop with its apex at the same height as a dipole typically has 1–2 dBd more gain toward the horizon due to its larger area and the effect of the base wire near ground level acting as a partial reflector. The delta loop's multi-band capability and single-mast installation requirement are additional practical advantages. The dipole is simpler to build and tune.
Can I use the delta loop beam on 40m in a suburban garden?
A 40 m two-element phased beam requires element spacing of 10.5 m and two loops each 42.8 m in circumference. The total footprint is roughly 14.3 m wide × 10.5 m deep — large for most suburban gardens. A single 40 m delta loop is far more practical: apex at 12–14 m height with a base 14.3 m wide. The single loop approach works well as a first low-band HF antenna when a tall tree is available.
What happens if the two elements are not exactly λ/4 apart?
Element spacing tolerates ±10–15% without catastrophic performance loss. If spacing is 10% off (λ/4 ± 10%), the forward gain drops slightly and the F/B ratio decreases by a few decibels. The phasing line length is more critical than the physical spacing — you can partially compensate for incorrect spacing by adjusting the phasing line length, but the optimal F/B ratio only occurs at both correct spacing and correct phasing simultaneously.
Is the phased delta loop beam better than a Yagi?
No — a 3-element Yagi provides 7.5 dBd gain vs the delta beam's 4–5 dBd, and is a more mature, well-understood design. The delta loop beam's advantage is its mechanical simplicity — it requires only a single tall central support rather than a full tower and rotator, making it accessible to operators who cannot install a conventional beam. Where the mechanical constraints permit, a Yagi is the better performer.
Can I switch the delta loop beam between vertical and horizontal polarisation?
Not conveniently in a fixed installation — the polarisation is set by the feed point position, which is a physical location on the wire. However, you can build the loop with two feed points (bottom corner and side midpoint) and switch between them with a relay, effectively switching polarisation electrically. This allows comparison between horizontal and vertical polarisation on a given path — occasionally useful for ionospheric polarisation matching experiments.
Does the base of the loop need to be at a specific height?
Higher is better for the base wire, within practical limits. A base wire at 2 m above ground loses significantly less to ground absorption than one at 0.5 m. For a 40 m loop with a 12 m apex, the base wire at 2 m above ground is fine — the sloping sides compensate for some ground proximity effect. Do not lay the base wire on the ground — ground contact causes high RF losses and shifts the resonant frequency unpredictably.