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Ideal Cable Transmission-Line Estimates

Estimate coaxial and two-wire cable parameters from idealized geometry.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

The worked inputs demonstrate the selected model; change a known value or leave an editable unknown empty for a supported inverse.

coax Z≈60ln(D/d)/√εr; two-wire Z≈120ln(2s/d)/√εr

Worked example

Enter these known values and leave the other values blank.

Cable Type
Coaxial
Inner conductor diameter (d)
1 μm
Inner diameter of surface shield (D)
4 μm
Substrate dielectric relative permittivity
2.25
Impedance
55.45 Ω
Capacitance
0.901 pF/cm
Delay
0.05003 ns/cm
Inductance
2.7726 nH/cm
Cutoff frequency
25441 GHz

Assumptions and limitations

  • The model assumes a uniform nonmagnetic dielectric and negligible conductor loss. Captured coefficients are rounded engineering approximations, not exact metrology.
  • The two-wire logarithmic formula is a widely separated conductor approximation; twist, proximity and frequency-dependent dielectric effects are excluded.
  • The cutoff output uses a rounded geometric wavelength proxy after correcting its GHz scale; an exact higher-mode limit requires an electromagnetic solution.

Common questions

What does this model assume?

The model assumes a uniform nonmagnetic dielectric and negligible conductor loss. Captured coefficients are rounded engineering approximations, not exact metrology. The two-wire logarithmic formula is a widely separated conductor approximation; twist, proximity and frequency-dependent dielectric effects are excluded.

How do units and inverse calculations work?

Choose compatible units for each quantity. The model converts quantities internally; supported editable fields can be solved from sufficient independent known values. Display rounding does not change the underlying value.

References

The captured GHz cutoff coefficient for dimensions in inches is 1000 times too small. The geometric wavelength proxy uses approximately 23.6 GHz-inches rather than 0.0236; all diameter and dielectric inverse branches use the same scale. This remains a rounded higher-mode cutoff approximation, not an exact electromagnetic eigenmode solution. Explicit model domains enforce physical bounds and strict whole-count membership where required. Explanatory image content is replaced by original dimension descriptions without changing its visibility.

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