Build a Moxon Rectangle Antenna
The Moxon rectangle is one of the most elegant compromises in amateur antenna design — a two-element beam that folds its elements back on themselves, reducing the boom length requirement to roughly 30% of a standard 2-element Yagi while delivering forward gain of 5–6 dBd and an exceptional front-to-back ratio exceeding 30 dB at the design frequency. Originally described by Les Moxon G6XN and popularized by L.B. Cebik W4RNL, the Moxon is particularly well-suited for 20m, 15m, and 10m operation where its compact footprint allows a rotatable beam installation on a simple push-up mast or short tower. This guide builds a 20m wire Moxon rectangle optimised for the full 20m band, mountable on a cross-frame support at any height above 20 feet.
The Folded Element Concept
A Moxon rectangle is a 2-element Yagi with the outer portions of both elements folded back toward the center, creating a rectangular shape. The folding achieves two things simultaneously: it reduces the physical width by about 70% compared to a standard Yagi, and it creates a capacitive coupling between the folded tips of the driver and reflector that dramatically improves the front-to-back ratio:
Moxon Dimensions — The Critical Parameters
The Moxon rectangle is defined by five dimensions that together produce the correct geometry for resonance and pattern. These dimensions are interdependent — changing one requires recalculating the others:
Why the Front-to-Back Ratio Is So Good
The Moxon's 30+ dB front-to-back ratio far exceeds that of a standard 2-element Yagi (10–15 dB). This makes it a genuinely different antenna for receive operation — signals coming from directly behind the antenna are attenuated by more than a factor of 1000 in power:
Moxon vs 2-Element Yagi vs 3-Element Yagi
Understanding how the Moxon fits into the beam antenna landscape helps choose the right antenna for each situation:
- vs standard 2-element Yagi: similar forward gain, much better F/B (30+ vs 10–15 dB), 70% smaller width. The Moxon is the better choice whenever compact size and excellent F/B matter more than maximum bandwidth.
- vs 3-element Yagi: about 1–2 dBd less forward gain, similar or better F/B at design frequency, dramatically smaller physical footprint. The Moxon on a short mast vs a 3-element on a tall tower — the tower wins for DX, but the Moxon wins for practical accessibility.
- Best use cases for the Moxon: operators with limited mast height or boom space; operators who rotate frequently (the lighter Moxon is faster to rotate); operators who primarily want excellent F/B ratio for interference rejection; and operators on 10m or 15m where the Moxon is physically small and trivially mountable on any mast.
- Wire vs aluminum construction: the Moxon is uniquely practical as a wire antenna on a lightweight frame — the non-parallel element geometry does not lend itself to standard tube construction, so wire with a support frame is the standard homebrew approach.
| Band | Frequency | A (width) | B (driver tail) | C (gap) | D (reflector tail) | E (depth B+C+D) |
|---|---|---|---|---|---|---|
| 10m | 28.40 MHz | 7.27 ft | 2.33 ft | 2.6 in | 2.43 ft | 4.99 ft |
| 12m | 24.94 MHz | 8.27 ft | 2.66 ft | 3.0 in | 2.77 ft | 5.68 ft |
| 15m | 21.20 MHz | 9.74 ft | 3.13 ft | 3.5 in | 3.26 ft | 6.68 ft |
| 17m | 18.10 MHz | 11.41 ft | 3.66 ft | 4.1 in | 3.82 ft | 7.82 ft |
| 20m | 14.15 MHz | 14.53 ft | 4.67 ft | 5.3 in | 4.87 ft | 9.98 ft |
| 40m | 7.150 MHz | 28.74 ft | 9.23 ft | 10.5 in | 9.62 ft | 19.72 ft |
Moxon 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 wire Moxon rectangle on a PVC cross-frame support
Why the Frame Matters
The Moxon rectangle's performance depends critically on maintaining the correct geometry — particularly the gap dimension C between the driver and reflector tips. A gap that is 1 inch too large or too small shifts the resonant frequency by 50–100 kHz and reduces the front-to-back depth. The frame must hold all dimensions accurately under wind loading and temperature variation:
PVC Cross-Frame Construction
The cross-frame uses four arms of 3/4-inch PVC pipe radiating from a central PVC cross fitting. Two arms support the driver corners and two arms support the reflector corners. The frame is attached to the mast at the central hub:
Building the 20m Moxon Rectangle
This guide builds a wire Moxon on a PVC cross-frame. All construction is done on the ground — the frame is assembled, the wire is routed, and the feedpoint is built before any part of the antenna is raised to height. The gap spacer is the most critical component and is built last after the wire layout is confirmed.
Build the PVC Cross-Frame
Cut four sections of 3/4-inch PVC pipe to 9 feet each. Insert all four sections into the 3/4-inch PVC cross fitting at the center — do not glue the arms into the cross fitting yet. Lay the cross flat on the ground and mark the arm orientation: two arms will point toward the driver corners, two arms toward the reflector corners. The cross arms point at 45° to the antenna axis — when you orient the frame so that the antenna front points North, the arms point NE, NW, SE, and SW.
At the tip of each arm, install a small plastic eye screw or wire hook — this is the corner support point for the wire. Drill a small hole through the PVC cap at each arm tip (or through the side of the PVC near the tip) for the wire to pass through or wrap around. The corner support point must be non-conductive — no metal hardware touching the wire at the arm tips.
Prepare the Wire Elements
Cut two lengths of wire: the driver wire at 24.5 feet and the reflector wire at 25.0 feet — both slightly longer than the calculated lengths to allow for trimming. Use #14 AWG stranded copper wire — stranded is more flexible than solid and handles repeated installation and removal better for a rotatable antenna.
Route the Driver Wire on the Frame
With the cross-frame laid flat on the ground at the correct orientation, route the driver wire from the center mark outward to the two driver-side arm tips, then back inward toward the antenna center (the gap side). The wire forms a U-shape:
- Start at the driver wire center mark — this is the feedpoint location, at the center of the front face of the rectangle
- Run the wire outward along the front face toward the left driver arm tip
- At the left arm tip (the corner), pass the wire through the eye hook and turn it 90° to run inward (toward the antenna center depth)
- The wire runs straight back toward the gap at a length of B = 4.67 ft
- The tip of the driver wire (at the gap end) hangs free for now — the gap spacer will position it correctly in a later step
- Repeat for the right side of the driver
Temporarily secure the wire to the arm tips with nylon zip ties looped over the wire — snug enough to hold position but easily adjustable for the tuning step. Do not make any permanent connection at this stage.
Route the Reflector Wire on the Frame
Route the reflector wire on the rear two arms of the cross-frame using the same U-shape routing as the driver. The reflector center mark is at the rear face center of the rectangle. The reflector tail wires run forward from the rear arm tips toward the gap, at a depth of D = 4.87 ft.
The reflector tip wires should now be approximately parallel to the driver tip wires, with both sets of tips pointing toward each other at the center of the antenna's depth. The gap between the driver tip wire and the reflector tip wire on each side should be approximately C = 5.3 inches. Measure this gap and note the actual measurement before building the gap spacer.
Build and Install the Gap Spacers
The gap spacer is a rigid non-conductive piece that holds the driver and reflector tip wires at exactly the correct spacing. It is the most critical mechanical component in the antenna:
With both gap spacers installed, the antenna geometry is complete and dimensionally locked. Re-measure all dimensions: width A, depths B and D, and gaps C. All measurements should be within tolerance. If any dimension is off, adjust now before the feedpoint assembly is connected.
Build the Feedpoint Assembly
The Moxon rectangle driver is a balanced antenna — the feedpoint is at the center of the driver element and both halves are of equal electrical importance. A current balun (1:1) is required at the feedpoint to prevent the coax from radiating and distorting the antenna pattern:
Solder the driver wire ends to the SO-239 terminals inside the feedpoint enclosure. The driver wire is split at the center with a small 1-inch gap — each half connects to one terminal. Seal the enclosure with RTV sealant around all wire and coax entry points.
Glue the Cross-Frame and Mount to Mast
Once all wire routing is verified and the feedpoint is installed, glue the PVC cross arms into the center fitting with PVC cement. Apply cement to both the pipe ends and the fitting sockets and push together quickly — PVC cement sets in 30–60 seconds. Verify all arms are fully inserted and aligned before the cement sets.
Mount the center PVC cross fitting to the mast using a 3/4-inch pipe clamp (the cross fitting's OD is approximately 1.3 inches — most 1.25-inch pipe clamps fit it snugly). Orient the cross so that the front-back axis aligns with the intended direction for initial testing. Route the coax down the mast from the feedpoint.
Raise and Measure SWR
Raise the antenna to its operating height. Connect the NanoVNA at the shack end of the coax. Sweep 13.5–15.5 MHz and look for the SWR minimum:
Verify Front-to-Back Performance and Document
The Moxon's exceptional front-to-back ratio is its signature characteristic — verify it on-air by pointing the antenna at a signal source and comparing S-meter readings front vs 180° rear. A properly built Moxon should show a 5+ S-unit (30+ dB) difference at the design frequency — a stronger indicator than any other antenna parameter that the geometry is correct.
If front-to-back is only 2–3 S-units (12–18 dB), the most likely causes are: incorrect gap spacing (measure and correct first), asymmetric gap (gaps on left and right sides not equal — correct), or element length mismatch between driver and reflector (measure each element total length and correct any discrepancy over 2 inches).
Document: all final wire lengths, gap measurements on both sides, SWR at resonance and at band edges, front-to-back measurement at design frequency and ±200 kHz from design, and antenna height. Weatherproof all connections, seal the feedpoint enclosure, and coat exposed wire solder joints with liquid electrical tape or silicone sealant.
When to Consider Aluminum Construction
The wire Moxon is the practical standard for most homebrew builds, but aluminum tube construction offers advantages for specific situations:
- Higher power operation: wire Moxon with the standard feedpoint handles legal limit power without issue — wire gauge is not a limiting factor for the antenna element itself. But for a permanent high-power installation, the aluminum element's more rigid geometry maintains the critical gap dimension more consistently through temperature extremes and wind loading.
- Permanent fixed installation: an aluminum Moxon on a small boom holds its dimensions without wind-induced sag or temperature creep. The wire Moxon can slowly change geometry over months as wire stretches and cable ties fatigue.
- 10m and 15m: at these higher frequencies the Moxon dimensions are small enough to make aluminum tube construction straightforward — a 10m Moxon uses elements under 8 feet wide. Bending 1/2-inch aluminum tubing into the U-shaped element geometry is manageable and produces a very stable, rigid antenna.
- Trade-off: aluminum Moxon elements are harder to build accurately to the critical gap dimension. The tube must bend at exactly the correct radius and stop at the correct depth — requiring a jig or careful measurement during bending. The wire approach is more forgiving of construction imprecision because the wire routing can be adjusted after the frame is built.
Moxon for 10m and 15m — Compact Rotatable Beam
The Moxon really shines on 10m and 15m where its small size makes it a practical rotatable beam on the simplest possible support:
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| No SWR dip visible in sweep | Feedpoint connection fault or driver wire open circuit | Check DC resistance from coax center to shield — should be a near-short (through the balun) | Check driver wire solder joints at feedpoint SO-239; verify balun winding is continuous |
| Front-to-back ratio only 2–3 S-units instead of 5+ | Gap dimension incorrect or asymmetric | Measure gap C on both sides — should be 5.3 inches ± 0.25 inch, equal on both sides | Adjust gap spacers to correct dimension; verify both sides equal; re-measure F/B |
| SWR minimum at correct frequency but minimum SWR is 3:1+ | Feedpoint impedance mismatch — element lengths wrong | Measure total driver wire length and reflector wire length — compare to targets | Adjust element tail lengths symmetrically; re-measure SWR after each adjustment |
| Resonance shifts after rain or high humidity | Water in feedpoint enclosure or on wire near feedpoint | Dry the feedpoint area and re-measure | Improve feedpoint weatherproofing; seal all wire entry points with RTV; add desiccant |
| SWR rises progressively over months | Wire stretching under tension; gap spacer moving | Re-measure all dimensions; compare to original documented values | Re-tension wire; replace worn gap spacers; re-verify all Moxon geometry dimensions |
| Pattern appears to have gain in wrong direction | Antenna mounted backward — reflector toward target | Swap front and rear — the driver side should point toward the target | Rotate antenna 180° on mast; driver (fed element) faces forward toward target |
| Wind causes geometry to shift — F/B degrades in wind | Wire sagging or gap spacer moving under wind load | Observe antenna during moderate wind — note which elements sag or shift | Add intermediate wire tensioners along arms; reinforce gap spacer attachment; use heavier wire gauge |
Is the Moxon really better than a 2-element Yagi?
For front-to-back ratio at the design frequency, yes — significantly. The Moxon's 30+ dB F/B versus a standard 2-element Yagi's 10–15 dB is a real and large difference. For forward gain, they are approximately equal — both produce around 5–6 dBd. The Moxon wins on compactness (70% narrower) and F/B; the standard 2-element Yagi wins on bandwidth (the Yagi's deep null is broader in frequency than the Moxon's) and on forward gain over a wider bandwidth. Which is "better" depends entirely on what you value — if F/B ratio for interference rejection is the priority, the Moxon is clearly better. If broadband gain is the priority, the standard Yagi is preferable.
Does the Moxon work well for FT8 and digital modes?
Yes — the Moxon's excellent front-to-back ratio is particularly valuable for digital mode operating. On a crowded FT8 frequency, being able to null out strong stations calling from the opposite direction (behind the antenna) allows the decoder to pull out weaker wanted signals that would otherwise be masked. The narrow Moxon null at the design frequency is ideally centered on 14.074 MHz (FT8) for a Moxon designed for 14.150 MHz — the null is within 100 kHz of FT8 and still 20–25 dB deep at that offset. FT8 operators who rotate their Moxon during busy band openings consistently report cleaner decoding than with a dipole or even a standard Yagi with shallower F/B.
Can I build a Moxon for 40m?
Yes — the 40m Moxon dimensions show a width of about 28.7 feet, which is considerably more manageable than a 65-foot 40m dipole. The depth is about 19.7 feet, making the total footprint approximately 28.7 × 19.7 feet — still substantial but rotatable on a modest tower. The trade-off on 40m is that wire construction becomes more difficult to keep dimensionally stable over the larger span, and the antenna needs to be at least 30–40 feet high to perform well on 40m. Many 40m Moxon builders use aluminum tubing for the element sections rather than wire, for better dimensional stability. At 40m, the Moxon's compactness advantage over a 65-foot dipole is valuable enough to justify the construction complexity.
How sensitive is the Moxon to the gap dimension?
Very — the gap is the most sensitivity-critical dimension in the design. A gap error of 0.5 inches shifts the resonant frequency by approximately 30–50 kHz and reduces the front-to-back ratio from 30+ dB to 15–20 dB. A gap error of 1 inch degrades F/B to approximately 10–12 dB — comparable to a standard 2-element Yagi. This is why the gap spacer must be rigid and accurately made. However, the good news is that the gap can be verified and corrected after the antenna is built and tested — lower the antenna, re-measure the gap on both sides, and adjust the spacers if needed. The Moxon is forgiving of element length errors (±1 inch is tolerable) but unforgiving of gap errors (±0.25 inch is the practical tolerance for >25 dB F/B).
What height is needed for the 20m Moxon to work effectively?
The same principles as any HF antenna apply — more height is always better, and the practical minimum for useful DX operation is around 25–30 feet (approximately λ/4 at 20m). At 25 feet the Moxon's main radiation lobe is at approximately 40° elevation — reasonable for medium-distance DX and domestic contacts. At 40 feet the lobe drops to 28° — significantly better for DX. At 50 feet (approximately λ/2) the lobe reaches 20° — excellent for worldwide DX. The Moxon's compact size and light weight make it easier to reach useful heights than a Yagi with a long boom — a 25-foot push-up mast with a small TV antenna rotator can support a 20m Moxon and provide useful DX performance that would require a full tower for a conventional Yagi.
Why is a current balun needed at the Moxon feedpoint?
The Moxon driver is a balanced antenna — like a dipole, the two halves of the driver element are symmetrical and carry equal and opposite currents. When an unbalanced coax feeds a balanced antenna without a balun, the coax shield carries common-mode current — it becomes part of the antenna. For a Moxon, this has two consequences: the coax changes the antenna's impedance from the design value and it carries RF current down to the mast and into the shack. A current balun (choke balun) prevents the coax shield from carrying RF. For the Moxon, a W2DU-type choke (a string of ferrite beads on the coax) or an FT-240-31 toroid with 5–6 coax turns is adequate. Without the balun, SWR will be unexpectedly high, the pattern will be distorted, and RF may appear in the shack.