Full-Wave Loop Calculator

How loop shape affects the build

The full-wave loop is a continuous conductor whose total electrical length is approximately one wavelength at the design frequency. The accompanying sketch shows the basic closed-loop geometry that the calculator is intended to size. A loop can be built as a square, rectangle, triangle or another practical shape, and that geometry affects the feedpoint impedance and radiation pattern even when the total wire length is similar.

The calculator provides a starting perimeter from frequency. Real construction requires a correction because the wire has finite diameter and the loop is installed at a finite height above ground. Insulation, nearby metal, trees, building materials and the feedline can also change the resonant frequency. A loop mounted close to the ground may behave very differently from one mounted several wavelengths high, particularly in its radiation pattern and feedpoint impedance.

Feedpoint location is therefore an important part of the design. A side or corner feed can be convenient and can provide different impedance characteristics from a top-centre feed. If the loop is balanced but is fed with coaxial cable, a suitable current balun or common-mode choke may help keep the feedline from becoming an unintended radiator. Build the loop slightly long, measure it in the intended shape, and trim carefully. Do not assume that a low SWR at one frequency means the loop is efficient; conductor loss, ground interaction and matching-network loss still matter. The sketch on this page is intentionally a simple representation of the loop so the calculation remains tied to the actual electrical concept rather than to a decorative generic antenna drawing.