1. What is Transmission Line Impedance?

The characteristic impedance (Z) of a transmission line is the ratio of voltage to current in a traveling wave. It's determined by the line's geometry and material properties, specifically its distributed inductance (L) and capacitance (C) per unit length.

2. How Does the Calculator Work?

The calculator uses the transmission line impedance equation:

Where:

• \( Z \) — Characteristic impedance (Ω)
• \( L \) — Inductance per unit length (H/m)
• \( C \) — Capacitance per unit length (F/m)

Explanation: The equation shows that impedance increases with higher inductance and decreases with higher capacitance.

3. Importance of Impedance Calculation

Details: Proper impedance matching is crucial for maximizing power transfer and minimizing signal reflections in RF systems, telecommunications, and high-speed digital circuits.

4. Using the Calculator

Tips: Enter the distributed inductance in henries per meter (H/m) and distributed capacitance in farads per meter (F/m). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical transmission line impedance values?
A: Common values are 50Ω (RF systems) and 75Ω (video/cable TV). Twisted pairs are typically 100-120Ω.

Q2: Why is impedance matching important?
A: Mismatched impedance causes signal reflections that can distort signals and reduce power transfer efficiency.

Q3: Does frequency affect characteristic impedance?
A: For ideal transmission lines, Z is frequency-independent. Real lines may show some frequency dependence at very high frequencies.

Q4: How does geometry affect impedance?
A: For coaxial cables, Z depends on inner/outer conductor diameters. For PCB traces, it depends on trace width, thickness, and dielectric properties.

Q5: What's the difference between characteristic impedance and input impedance?
A: Characteristic impedance is a property of the line itself, while input impedance depends on both the line and its termination.