Microstrip Line Overview
Microstrip is the most common transmission line structure in PCB design. It consists of a flat conductor on top of a dielectric substrate, with a solid ground plane on the bottom. This simple structure carries high-frequency signals across a board with predictable electrical behavior.
Controlling impedance is key when engineers design RF circuits, antennas, or high-speed digital boards. If the impedance of a trace does not match the rest of the circuit, signals reflect back. That causes noise, data errors, and power loss. Microstrip calculators help engineers get the impedance right before manufacturing starts.
The characteristic impedance (Zo) of a microstrip line depends on three physical dimensions: the trace width (W), the substrate height (h), and the copper thickness (t). It also depends on the dielectric constant (εr) of the board material. A wider trace produces lower impedance. A thicker substrate produces higher impedance. FR4, the most common PCB material, has an εr of about 4.2 to 4.8.
At higher frequencies, the effective permittivity (εr eff) becomes important. It describes how the electromagnetic field spreads between the trace and the surrounding air. This value is always lower than the substrate’s εr because part of the field travels through air.
This calculator uses the Hammerstad-Jensen model. It’s one of the most accurate formulas for microstrip impedance. It supports two modes. Analyze mode takes a trace width and returns the impedance. Synthesis mode takes a target impedance and returns the required trace width.
Use this tool during PCB layout to verify your trace geometry before sending files to the manufacturer. It works for standard FR4 boards as well as high-frequency laminates like Rogers or PTFE-based materials.