Coaxial Cable Loss

Formula

Description

Coaxial cable attenuation is dominated by conductor losses at lower frequencies and dielectric losses at higher frequencies. The conductor loss component is approximately R/(2Z₀) where R is the total resistance per unit length of the inner and outer conductors (including skin effect). At higher frequencies, the dielectric loss term (proportional to frequency and dielectric loss tangent) becomes significant. Total cable loss increases with frequency (roughly as √f for conductor loss) and is the primary factor limiting cable run lengths in RF and broadband systems.

Variables

• α — Attenuation coefficient (dB/m, approximate)
• R — Conductor resistance per meter (Ω/m, including skin effect)
• Z₀ — Cable characteristic impedance (Ω)

Practical Notes

This formula gives only the conductor loss component. For a complete model, add dielectric loss: α_total = α_conductor + α_dielectric. Typical losses at 1 GHz: RG-58 ≈ 0.7 dB/m, RG-213 ≈ 0.27 dB/m, LMR-400 ≈ 0.11 dB/m. Lower impedance cables (Z₀ = 50 Ω) have slightly higher loss than higher impedance cables (Z₀ = 75 Ω) of the same size because more current flows for the same power. Always use manufacturer-specified loss curves for accurate link budget calculations.