Transmission Line Stub Calculator

A stub is a shunt (parallel) section of terminated transmission line used for impedance matching or filtering. Its length is chosen so that it presents a target susceptance — cancelling an unwanted reactance. Short-circuit stubs are lower loss; open-circuit stubs avoid vias on PCBs.

Equations & Parameters ▸

\(\ell_{SC} = \tfrac{1}{\beta}\arctan\!\left(\tfrac{Y_0}{B}\right)\)

f	Operating frequency.
Z₀	Stub characteristic impedance (Ω). Typically 50 Ω.
B	Target shunt susceptance (mS). Positive = capacitive, negative = inductive.
Type	Short-circuit: lower loss, needs via. Open-circuit: no via, slightly higher loss.

Physical constants used

c	Speed of light = 2.998×10⁸ m/s
µ₀	Permeability of free space = 4π×10⁻⁷ H/m ≈ 1.2566×10⁻⁶ H/m
ε₀	Permittivity of free space = 8.854×10⁻¹² F/m

Inputs

Frequency, f

Line impedance, Z₀

Stub characteristic impedance

Target susceptance, B

+ve = capacitive load

Stub termination

Results

Stub Length

Electrical length (°)—

Physical length—

λ/4 reference—

Diagram

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