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Moxon antenna calculator

Why this is not “a two-element Yagi”

A Moxon is two elements whose ends are folded towards each other and almost touch. That pair of folds does two things at once: it gives about 25 dB of front-to-back and it brings the feedpoint impedance down to exactly 50 Ω. The price is a narrow bandwidth and a gap between the ends that is very critical indeed.

50 ΩABCDEreflector
The gap C between the ends is the most critical dimension of the whole thing
Frequency (MHz)
Conductor diameter (mm)
Dimensions
A — width
B — driven element bend
C — gap between the ends
D — reflector bend
E — overall depth (B + C + D)
Total wire length
Characteristics
Gain (free space)
Front-to-back ratio
Input impedance
d/λ ratio
The dimension polynomials come from L. B. Cebik, W4RNL, «Designing Moxon Rectangles by Equation and by Model» (the same ones used in Dan Maguire AC6LA's MoxGen).

📐 The formulas​

The dimensions come from L. B. Cebik’s (W4RNL) polynomials, fitted to NEC modelling results. The argument x is the base-10 logarithm of the conductor diameter in wavelengths:

x = log10( d / λ )

A = (−0.0008571428571·x² − 0.009571428571·x + 0.3398571429) × λ
B = (−0.002142857143·x² − 0.02035714286·x + 0.008285714286) × λ
C = ( 0.001809523381·x² + 0.01780952381·x + 0.05164285714) × λ
D = ( 0.001·x + 0.07178571429) × λ
E = B + C + D

Symbols:​

  • A — width of the rectangle (along the elements)
  • B — the folded end of the driven element
  • C — the gap between the driven element and reflector ends
  • D — the folded end of the reflector
  • E — overall depth of the structure
Where this calculator stops:
  • The polynomials hold for d/λ between 1·10⁻⁵ and 1·10⁻²; outside that range the calculator warns you
  • The dimensions assume elements of constant diameter; telescoping tubing needs an equivalent diameter
  • The 5.8 dBi gain and 25 dB F/B are modelled free-space figures; over ground they are different
  • Cebik himself stressed that the equations have no physical meaning — they are a fit within the data

🎯 In practice​

  • A light directional antenna for 20 m. Roughly 7.7 × 2.8 m — half the size of a two-element Yagi.
  • A portable antenna for 10–15 m. Two wires and four spreaders.
  • A receive antenna with a deep rear null — a Moxon rejects backwards better than any two-element Yagi.
Practical advice:
  1. Hold the gap C more accurately than any other dimension — it is what sets the F/B.
  2. 50 Ω out of the box means all you need is a choke on the feedline, not a matching network.
  3. Tune for the middle of the segment you actually work: the bandwidth is narrow.
  4. Before you cut anything, check the result against MoxGen — it is the same arithmetic, and the two should agree exactly.

© 2026 UR3PKI · CyberDev.Space · Content licensed under CC BY-NC-SA 4.0.

How to cite this calculator
UR3PKI. «Moxon antenna calculator». CyberDev.Space. https://cyberdev.space/en/radio/calculators/antennas/moxon (licence CC BY-NC-SA 4.0).

The licence lets you use this material freely, including in teaching materials, but only with attribution to the author and a link to the source.

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