Double Stub Matcher

Smith Chart · Transmission Line Design Tool · v2.0

Idle

Load & Line Parameters

Load Impedance Z_L

jΩ

Z_L = R + jX · supports negative X (capacitive)

Characteristic Impedance Z₀

Typically 50 Ω (coax) or 75 Ω (cable TV)

Optional

Frequency

MHz

εᵣ

⊏⊏

Double Stub Configuration

Stub Separation d

Stub 1 Offset from Load d₀

Stub Termination

⊥ Short Circuit ○ Open Circuit

Applies to both stubs · SC: b = −cot(2πℓ) · OC: b = +tan(2πℓ)

Display Solutions

Quick Guide

Enter Z_L and Z₀ · complex loads supported

Set stub separation · λ/4 is most versatile

Optionally offset Stub 1 from load to escape forbidden zone

Choose SC or OC termination

Click Design Double Stub

d₀: = load → Stub 1 distance (λ)
d: = Stub 1 → Stub 2 distance (λ)
ℓ₁, ℓ₂: = stub lengths to find (λ)
g₁: = normalised conductance at Stub 1

⚠ Forbidden zone: loads with g₁ > 1/sin²(2πd) cannot be matched with the chosen spacing. Adjust d₀ or d to resolve.

Load Z_L

|Γ_L| circle

Sol 1 path

Sol 2 path

Match point

g=1 circles

Matching Solutions

Both solutions yield Z_in = Z₀ after stub insertion

Reflection & VSWR (Before Matching)

Parameter	Value

Normalised Values & Conventions

Parameter	Value

Solution 1 — Full Detail

Parameter	Value

Solution 2 — Full Detail

Parameter	Value

✓

Verification — Solution 1

Parameter	Value

✓

Verification — Solution 2

Parameter	Value

Copied!