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Coaxial Line Calculator

Compute impedance Z₀, capacitance/inductance per metre, TE₁₁ cutoff frequency, wavelength, skin depth and total attenuation (dielectric + conductor) for coaxial transmission lines.

// Parameters

Inner Conductor Diameter (d)

Outer Conductor Inner Diameter (D)

Target Impedance (Z₀)

Inner Conductor Diameter (d)

Relative Permittivity (εr)

—

Loss Tangent (tan δ)

—

Frequency

⚠ D must be greater than d.

Quick Presets

// Results

⚡

Enter parameters and click Calculate

Impedance (Z₀)—Ω

Outer Diameter (D)—mm

D/d Ratio—

Capacitance / Length—pF/m

Inductance / Length—nH/m

Cutoff Freq (TE₁₁)—GHz

Wavelength (λ)—mm

λ/4 Length—mm

λ/2 Length—mm

Phase Velocity—× c

Skin Depth (δs)—μm

Dielectric Loss (αd)—dB/m

Conductor Loss (αc)—dB/m

Total Attenuation—dB/m

Attenuation per 10 m—dB

Coaxial Line
Z₀ = (60/√εr)·ln(D/d) · C = 2πε₀εr/ln(D/d) F/m
L = (μ₀/2π)·ln(D/d) H/m · f_c(TE₁₁) ≈ 2c/(π√εr·(D+d))
αc = (Rs/2π)·(1/d+1/D) / (Z₀·η/2π) dB/m
αd = 27.3·√εr·tan δ / λ₀ dB/m
Rs = √(πfμ₀/σ) · δs = 1/√(πfμ₀σ)

About the Coaxial Line Calculator

Coaxial cable is the most common RF transmission line for connecting equipment and carrying signals over distances. It consists of an inner conductor surrounded by a dielectric and an outer conductor (shield). The characteristic impedance is set by the ratio of outer to inner diameter and the dielectric constant.

Why 50 Ohm?

The 50 ohm standard is a compromise between two conflicting requirements. Maximum power transfer in air-filled coax occurs at about 30 ohm, while minimum attenuation occurs at about 77 ohm. The geometric mean of these, roughly 50 ohm, was chosen as the RF standard. 75 ohm is used for broadcast and cable TV where signal loss (not power) is the priority.

Common Cable Types

RG-58 is a thin 50 ohm cable with 0.9 mm inner diameter and 2.95 mm outer diameter, rated to about 400 MHz for reliable use. RG-316 is a miniature 50 ohm cable used in test equipment and tight spaces. LMR-400 is a low-loss 50 ohm cable with 2.74 mm inner conductor, widely used for antenna feedlines where loss over long runs matters.

TE11 Cutoff Frequency

At sufficiently high frequencies, coaxial cable supports higher-order modes in addition to the dominant TEM mode. The TE11 cutoff frequency marks where the cable transitions from single-mode to multimode operation, which causes signal distortion. For RG-58, this limit is approximately 10 GHz.