The microstrip impedance calculator allows you to determine the characteristic impedance and propagation delay of a microstrip line based on its width, conductor thickness, dielectric thickness, and relative dielectric constant.
This tool is useful for PCB designers and RF engineers who want to optimize the performance of microstrip traces.
Formula used
Z₀ = function (W_eff, H, ε_eff)
with W_eff = corrected effective width of the microstrip line
ε_eff = effective permittivity calculated using the Hammerstad method
TD = propagation delay = √(ε_eff) / c, converted to ps/inch
Explanation
The effective width W_eff takes into account the correction of the conductor thickness according to the Wheeler method in order to better match the target impedance Z₀.
The effective permittivity ε_eff depends on the ratio between the effective width and the thickness of the dielectric.
The characteristic impedance Z₀ increases with smaller width or thicker dielectric, and decreases with higher relative permittivity.
The propagation delay TD indicates the time required for a signal to cross the microstrip line and is influenced by ε_eff.
Calculation example
For a microstrip line with:
W = 2 mils , t = 1 mil , H = 5 mils , εr = 4.5 :
– Effective width W_eff calculated with correction
– Effective permittivity ε_eff ≈ 3.8
– Characteristic impedance Z₀ ≈ 50.1234 Ω
– Propagation delay TD ≈ 91.4567 ps/inch
Benefits and Use
- Allows microstrip lines to be precisely sized to match a desired impedance.
- Optimizes signal and RF performance on printed circuit boards.
- Useful for calculating propagation delays and analyzing high frequency signals.
- Facilitates the choice of materials and dimensions for microstrip traces.
