Moxon Rectangle Antenna Calculator

Methodology & Design Notes

The engineering behind the dimensions: the Moxon rectangle bends a driven element and a reflector into two facing "C" shapes, with the folded tips (B and D) capacitively coupled across a small gap (C). That coupling is what gives the Moxon its excellent front-to-back ratio and a feedpoint impedance that lands close to 50Ω without a matching network — in a space only about 70% the width of a full 2-element Yagi. Dimensions here use L.B. Cebik's (W4RNL) full MoxGen regression, which is a function of both frequency and element diameter: A, B, and C follow 2nd-order curves in log₁₀(diameter/λ), D follows a 1st-order (linear) one, and E = B+C+D with F (the corner-to-corner diagonal, handy for sizing spreaders) derived geometrically. This was verified against Cebik's own published 2m reference table (0.5" tubing) to within 0.04" on dimension A before shipping. Gap C is the single most critical dimension — Cebik's own notes recommend holding it within about 3mm (1/8") of the calculated value, since it controls the tip coupling that the whole design depends on.

Why element diameter matters: thicker elements have more shunt capacitance to free space, which electrically lengthens them — so they need to be cut physically shorter to resonate at the same frequency. This effect is large enough on a Moxon to matter: swapping thin wire for 1/2" aluminum tubing at 20m shifts the overall width (A) by several feet, not a rounding error. Enter your actual element diameter to get dimensions tuned to your build, whether that's wire, thin tubing, or thick tubing — the model is valid from 0.00001λ to 0.01λ in diameter (a wide range covering everything from thin wire to several inches of tubing at HF), and the calculator will flag it if you go outside that.