Build a 10m Moxon Rectangle Antenna
The Moxon rectangle packs a surprising amount of directional performance into a compact, flat frame that is roughly 70% of the boom length of a 2-element Yagi. With 5–6 dBd of forward gain and a front-to-back ratio that regularly exceeds 30 dB at the design frequency, it outperforms a 2-element Yagi on F/B while feeding directly to 50 Ω coax with no matching network required. At 10 m, the entire antenna fits into a 2.5 × 1.3 m frame — ideal for rooftop, balcony, or attic mounting.
How the Moxon Rectangle Works
The Moxon rectangle was developed by Les Moxon (G6XN) and further refined by L.B. Cebik (W4RNL), whose published equations remain the standard design tool today. It is essentially a 2-element beam — a driven element and a reflector — where each element is folded back on itself to bring its tips close together at the ends of the rectangle. The folded tips add capacitive coupling between the driven element and reflector that modifies the current distribution in a way that dramatically improves the front-to-back ratio without additional elements.
The geometry produces five key dimensions: A (the driven element's main section), B (each driven element tail), C (the gap between the driven element tail and the reflector tail), D (each reflector tail), and E (the reflector's main section). The resulting antenna is inherently close to 50 Ω resistive at resonance — direct coax feed without a matching network is one of the Moxon's most practical advantages over the Yagi.
Moxon Dimensions — Cebik Equations
The following dimensions are calculated using Cebik's equations for a wire Moxon optimised at 28.5 MHz. Two build options are given: a wire-on-frame version (easier, lighter, suitable for portable or temporary use) and an aluminium tube version (more durable, better suited to permanent outdoor mounting).
Aluminium Tube Version — Construction Notes
For a permanent outdoor installation, the aluminium tube Moxon is far more durable than a wire version. The construction uses 19 mm OD aluminium tube for the main element sections, with the corners formed by aluminium angle or by bending tube using a conduit bender. The tails run from the corners toward the opposing element, with a precise gap spacer at each pair of facing tips.
- Dimension shortening: all five dimensions require a slight shortening (multiply by 0.97) to account for the larger conductor diameter's velocity factor effect — already incorporated in the calculator when "aluminium tube" is selected.
- Corners: can be formed with 90° aluminium elbows or by cutting 45° mitre joints and bolting with 3 mm aluminium gusset plates.
- Gap spacer: must mount the two facing tube ends rigidly and non-conductively at precisely the C dimension — PTFE rod or HDPE plastic block drilled to accept the tube ends works well.
- Feed point: requires a split at the DE centre — cut the main DE tube at its midpoint and separate the two halves by 20 mm. Connect an SO-239 or N-type connector between the halves with short copper straps. A 1:1 current balun at this point is strongly recommended.
- Mast attachment: mount on a non-conductive boom section or use an isolation plate to prevent the mast from coupling into the antenna pattern.
| Dimension | Description | 28.0 MHz (m) | 28.5 MHz (m) | 29.0 MHz (m) | 29.5 MHz (m) |
|---|---|---|---|---|---|
| A | DE main section | 4.809 | 4.725 | 4.643 | 4.565 |
| B | DE tail (each side) | 0.612 | 0.601 | 0.591 | 0.581 |
| C | Gap (critical) | 0.157 | 0.154 | 0.151 | 0.149 |
| D | Reflector tail (each side) | 0.766 | 0.752 | 0.739 | 0.727 |
| E | Reflector main section | 4.775 | 4.691 | 4.610 | 4.532 |
| Overall width (≈A) | — | 4.809 | 4.725 | 4.643 | 4.565 |
| Overall depth (B+C+D) | — | 1.535 | 1.507 | 1.481 | 1.457 |
The gap C is the most critical dimension. Errors in A, B, D, or E of ±10 mm shift the resonant frequency slightly but the antenna still works. An error in C of ±20 mm significantly degrades the front-to-back ratio — the capacitive coupling that creates the Moxon's excellent F/B depends on this gap being correct. Cut and set the gap dimension with care.
Moxon Rectangle Dimension Calculator (Cebik equations)
Materials for 10m wire Moxon (28.5 MHz design)
Frame Construction — Wire Version
The wire Moxon is the fastest build option and is ideal for portable use, attic installation, or as a proof-of-concept before committing to a permanent aluminium tube version. Allow 3–5 hours for the complete build.
Build the central hub and spreader arms
Cut four spreader arm pieces from 8 mm fibreglass rod: two horizontal arms each 2.40 m long (extending 1.20 m each side from the hub for a 28.5 MHz design), and two depth arms each 0.78 m long. Join them at a PVC cross fitting or lash together with UV-resistant cable ties and two-part epoxy. The hub becomes the mast attachment point — drill a central hole for a M10 bolt or U-bolt clamp.
Cut and prepare the driven element wire
The driven element total length is A + 2×B = 4.725 + 2×0.601 = 5.927 m at 28.5 MHz. Cut a single piece of wire to this length. Find the centre and mark it — this is the feed point. Strip 30 mm at the centre and 30 mm at each tip end. The wire forms a U-shape: the straight horizontal portion (A = 4.725 m) runs along the front of the frame, and the two tails (B = 0.601 m each) hang down toward the reflector along the depth arms.
Cut and prepare the reflector wire
The reflector is a single continuous piece: E + 2×D = 4.691 + 2×0.752 = 6.195 m. This forms the same U-shape as the driven element, with the main section at the rear of the frame and the tails pointing forward toward the driven element. Strip 30 mm at each tail tip end only — the reflector has no feed point.
Mount the wires on the frame and set the gap C
Attach the driven element to the frame using small cable ties every 300–400 mm along the horizontal section, and secure the tails along the depth spreader arms. Do the same for the reflector. At the four inner corners of the rectangle, insert a non-conductive PTFE or acrylic spacer block to hold the gap C (0.154 m = 154 mm at 28.5 MHz) precisely. Fix the tips to the spacer with cable ties.
Install the feed point
At the centre of the driven element, solder the coaxial cable to the two wire ends. The coax inner conductor connects to one wire half, the coax outer (braid) to the other. Install a 1:1 current choke immediately at the feed point — wind 8 turns of feedline coax through an FT-114-31 or FT-240-31 toroid, or thread the coax through 5–6 ferrite beads. Mount the feed assembly in a small weatherproof box glued to the front spreader arm.
Initial SWR check and trim
Mount the antenna at operating height — even a temporary installation at 5 m is sufficient for initial tuning. Connect a NanoVNA or antenna analyser at the feed point (short coax only — the choke should be immediately at the feed). Sweep 27–30 MHz and find the frequency of minimum SWR. If the minimum is above 28.5 MHz, lengthen the driven element by 30 mm per side and re-check. If below, shorten by 20 mm per side.
| Frequency (MHz) | Gain (dBd) | F/B (dB) | SWR (50 Ω) | Notes |
|---|---|---|---|---|
| 28.000 | 4.8 | 12 | 2.2:1 | Lower band edge — reduced F/B |
| 28.300 | 5.2 | 22 | 1.4:1 | CW portion — good performance |
| 28.500 | 5.5 | 32 | 1.1:1 | Design frequency — peak F/B |
| 28.700 | 5.3 | 25 | 1.3:1 | SSB portion — very good |
| 29.000 | 5.0 | 18 | 1.7:1 | FM/satellite — acceptable |
| 29.500 | 4.5 | 12 | 2.5:1 | Upper edge — ATU may help |
The Moxon's secret weapon: that 30–35 dB front-to-back ratio at the design frequency is extraordinary — a 3-element Yagi typically achieves only 20–25 dB F/B. In a contest or DX pileup situation, the ability to null out a station coming from behind by 30 dB while keeping full gain forward makes the Moxon one of the most operationally useful compact beams available to the home builder.
| Parameter | Moxon Rectangle | 2-element Yagi | Advantage |
|---|---|---|---|
| Forward gain | ~5.5 dBd | ~5.0 dBd | Moxon +0.5 dBd |
| F/B ratio (peak) | 30–35 dB | 10–15 dB | Moxon +15–20 dB |
| Boom length (10m) | ~1.5 m depth | ~2.0 m boom | Moxon 25% shorter |
| Width | ~4.7 m | ~5.0 m (element) | Similar |
| Feed point Z | ~50 Ω direct | ~25 Ω — needs match | Moxon simpler |
| SWR 2:1 bandwidth | ~800 kHz | ~1,000 kHz | Yagi wider |
| Wind loading (10m) | Low — compact | Moderate | Moxon lower |
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| SWR will not go below 2:1 | Gap C incorrect | An excessively large gap prevents the capacitive coupling that makes the Moxon resonate at 50 Ω — the feed point impedance rises above 50 Ω and SWR with it. A gap that is too small drives the impedance below 50 Ω | Measure C precisely and adjust. The correct gap produces SWR of 1.1–1.3:1 at the design frequency with no matching network |
| Good SWR but poor F/B — antenna sounds like a dipole | Overall dimension balance off | Run the Cebik equation calculator and compare your physical dimensions against the calculated values. The B and D dimensions primarily control the F/B ratio | Correct B and D to calculated values. Also verify the reflector is not accidentally making electrical contact with the frame or mast |
| SWR varies dramatically with coax position | Common-mode current on the coax braid changing the effective antenna geometry | Without a choke, the feedline becomes part of the antenna and degrades the pattern significantly | Install a current choke (1:1 current balun) immediately at the feed point |
Can I build a Moxon for other HF bands?
Yes — the Cebik equations work for any frequency. Just enter your target frequency into the calculator. A 20 m Moxon has A ≈ 9.5 m wide and depth ≈ 3.0 m — large but manageable as a wire-on-frame antenna. A 15 m Moxon fits into roughly 6.7 × 2.1 m — very practical. On 6 m the antenna fits 1.65 × 0.52 m — small enough for an attic installation. The 20m Moxon build guide is also on this site.
Does the Moxon need a balun?
The feed point is balanced (two symmetric halves of the driven element) but fed with unbalanced 50 Ω coax. A 1:1 current balun is strongly recommended — without it, common-mode current on the coax distorts the excellent F/B ratio that makes the Moxon special. The 1:1 choke adds nothing to match the impedance (the Moxon is already 50 Ω) but dramatically improves pattern symmetry and reduces RF in the shack.
Can I use the Moxon vertically polarised?
Yes — rotate the antenna 90° so the elements run vertically. The radiation pattern rotates with the antenna: the figure-8 pattern becomes bidirectional in the now-horizontal plane, with the forward direction being toward the front face of the rectangle. Vertically polarised Moxons are used for VHF/UHF portable work and as low-mounting HF arrays.
How does the Moxon compare to the Yagi for contesting?
The 3-element Yagi beats the Moxon on forward gain by about 2 dBd — a meaningful operational advantage for chasing weak DX. However, the Moxon's 30+ dB F/B ratio gives it a significant advantage in high-QRM contest conditions where stations directly behind the beam are causing interference.
Will the Moxon work on other bands without a tuner?
The Moxon is inherently a single-band antenna — its performance depends critically on maintaining the correct element proportions for a specific frequency. On adjacent bands the SWR is typically 3:1 or higher. For multi-band operation from a single compact antenna, a fan dipole or EFHW with an ATU is more practical.
What is the take-off angle from a Moxon at 8m height?
At 8 m height on 10 m (approximately 0.76λ), the elevation pattern shows a main lobe at about 22°. This is a good DX take-off angle for 10 m propagation. Increasing height to 12 m (1.13λ) lowers the take-off angle to approximately 15°, improving long-distance DX performance.