Microstrip Impedance Calculator
Compute the characteristic impedance (Z₀) of a PCB outer-layer transmission line from trace geometry and substrate dielectric constant.
Design Parameters
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Common Dielectric Constants:
- FR-4: 4.2 – 4.6 (default 4.4)
- Rogers 4350 (RF): 3.48
- Vacuum / Air: 1.0
- FR-4: 4.2 – 4.6 (default 4.4)
- Rogers 4350 (RF): 3.48
- Vacuum / Air: 1.0
Characteristic Impedance Results
Characteristic Impedance (Z₀)48.46Ω
Propagation Delay140.70ps/inch
Microstrip Cross-Section Model
Microstrip Transmission Line Theory
A microstrip places a signal trace on the outermost copper layer of a PCB directly above an inner ground plane. The electromagnetic coupling between the trace and the ground reference forms a controlled-impedance transmission line used for RF and high-speed digital signals.
Why Impedance Matching (50Ω / 90Ω) Matters
At high frequencies or fast rise times, any impedance discontinuity along a signal path creates reflections that cause undershoot, overshoot, and jitter.
- Single-Ended 50Ω: The universal standard for RF transmission lines, antenna feeds, and clock traces worldwide.
- Differential 90Ω / 100Ω: The coupled-pair target for USB, Ethernet, and PCIe differential signals.