Balanced line with square conductors calculator
When you need this
When the line is made not from wire but from square bar or extrusion — in high-Q resonators, in amplifier matching sections, and in rigid structures where the conductor has to hold its own shape.
| Gap between conductors g (mm) | |
| Square side d (mm) | |
| Result | |
| Characteristic impedance Z₀ | |
| Centre-to-centre spacing D | |
📐 The formulas
Characteristic impedance (conductors in air):
D = g + d
Z₀ = 105.2 × ln(2.475 × D/d − 1.3359)
Symbols:
g— the gap between the conductors [mm]d— the side of the square section [mm]D— centre-to-centre spacing [mm]
Where this calculator stops:
- The formula is empirical: the error grows once the gap becomes smaller than the conductor side
- The calculation assumes air filling and conductors of equal section
- The faces must be turned towards each other, not set corner-on
🎯 In practice
- Rigid lines from extrusion in power amplifiers and filters.
- Busbar assemblies distributing power in antenna systems.
- Comparison with round wire: a square of the same “thickness” gives a slightly lower impedance, thanks to its greater perimeter.
Practical advice:
- Sharp corners concentrate the field — at high power, chamfer them or use an extrusion with rounded edges.
- Keep the conductors parallel: a few degrees of skew changes the impedance noticeably over a long run.
- If the section is rectangular rather than square, use the side facing the other conductor, and check the result with an analyser.
© 2026 UR3PKI · CyberDev.Space · Content licensed under CC BY-NC-SA 4.0.
How to cite this calculator
UR3PKI. «Balanced line with square conductors calculator». CyberDev.Space. https://cyberdev.space/en/radio/calculators/lines/square_line (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.