Microstrip Impedance Calculator

Cross-sectional diagram of a microstrip structure with dimensions labeled: width (W), height (H), conductor thickness (T), and substrate permittivity (Er)

 

Provide values for H, T, W and the relative permittivity of the dielectric and click the button corresponding to unknown parameter Zo to calculate its value. ( 0.1< W/H < 3.0; 1 < εr < 15 )

 

Select the units for all dimensions: mm mils  
H (Dielectric thickness) : mm mils
T (Trace thickness) : mm mils
W (Trace width) : mm mils
εr (Relative permittivity) :
(Characteristic impedance): ohms
C0    (Capacitance): pF/cm pF/inch
Tpd  (Propagation delay time): psec/cm psec/inch

Notes:

  • The formulas used here are taken from the Design Guide for Electronic Packaging Utilizing High-Speed Techniques (4th Working Draft, IPC-2251, February 2001).
Microstrip Formula
  • Range of valid parameters specified in the Design Guide: 0.1< W/H < 3.0; 1 < εr < 15;
  • Accuracy: For typical PCB parameters (εr = 4, H = 30 mil and T = 1.37 mil), the deviation of the calculated results from results obtained using XFX, a 2D numerical field solver from Innoveda, is listed below:
Zo:  
0.1 < W/H < 0.2 within 5%
0.2 < W/H < 1.5 within 2%
1.5 < W/H < 2.0 within 5%
2.0 < W/H < 2.7 within 10%
2.7 < W/H < 3.0 within 15%
Co:  
0.1 < W/H < 0.2 within 10%
0.2 < W/H < 1.2 within 5%
1.2 < W/H < 2.0 within 10%
2.0 < W/H < 3.0 within 5%