Coax Power Handling

The peak power a coaxial line can carry is limited by voltage breakdown of the dielectric, where the field is highest — at the surface of the inner conductor. From the conductor diameters, dielectric constant and dielectric strength, this tool gives the characteristic impedance, the breakdown voltage, and the matched-line peak power. (Average/CW power is set by conductor heating and is cable- and cooling-specific — treat the peak figure as an upper bound and derate generously.)

Equations & Parameters ▸

\(Z_0=\dfrac{60}{\sqrt{\varepsilon_r}}\ln\dfrac{b}{a} \qquad V_{max}=E_{bd}\,a\,\ln\dfrac{b}{a} \qquad P_{peak}=\dfrac{V_{max}^2}{2\,Z_0}\)

d	Inner conductor diameter (mm); a = d/2.
D	Dielectric (shield inner) diameter (mm); b = D/2.
ε_r	Dielectric constant (PTFE 2.1, PE 2.25, air 1).
E_bd	Dielectric strength (kV/mm). PTFE ≈ 60–170, PE ≈ 20–28, dry air ≈ 3.

Reference: Standard coaxial-line field analysis (Pozar, Microwave Engineering). Peak power assumes a matched line; derate for VSWR, altitude and surface finish.

Inputs

Inner dia, d

Centre conductor

Dielectric dia, D

Shield inner

ε_r

Dielectric

Strength, E_bd

kV/mm

Breakdown field

Results

Line

Characteristic impedance Z₀—

Breakdown voltage V_max—

Power

Peak power (matched)—

Peak power (dBm)—

Diagram

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