1. What is a Microstrip Impedance Calculator?

Definition: This calculator estimates the characteristic impedance of a microstrip transmission line on a PCB based on its physical dimensions and substrate properties.

Purpose: It helps PCB designers and RF engineers design proper impedance-controlled traces for high-frequency circuits.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Z \) — Characteristic impedance (ohms)
• \( \epsilon_r \) — Relative permittivity of the substrate (dimensionless)
• \( h \) — Height of the substrate (meters)
• \( w \) — Width of the trace (meters)
• \( t \) — Thickness of the trace (meters)

Explanation: The formula accounts for the electromagnetic field distribution between the trace and ground plane.

3. Importance of Microstrip Impedance

Details: Proper impedance matching minimizes signal reflections, ensures signal integrity, and prevents power loss in high-frequency circuits.

4. Using the Calculator

Tips: Enter the substrate's relative permittivity (typically 4.3 for FR4), height (1.6mm for standard PCBs), trace width and thickness (35μm for 1oz copper). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical impedance target?
A: Common targets are 50Ω for RF systems and 75Ω for video applications, though specific requirements vary.

Q2: How accurate is this formula?
A: It's accurate to within 2% for w/h ratios between 0.1 and 3.0 and εr between 1 and 15.

Q3: What affects microstrip impedance most?
A: The trace width-to-height ratio (w/h) has the greatest impact, followed by the substrate's εr.

Q4: How do I adjust for different copper weights?
A: Standard 1oz copper is ~35μm thick. For 2oz (70μm), enter the correct thickness value.

Q5: What about coplanar waveguide or stripline?
A: Different formulas are needed for those transmission line types.