Coplanar Waveguide With Ground Characteristic Impedance Calculator

   The characteristic impedance (Zo) of coplanar waveguide with ground or microstrip lines with signal side ground plane can be calculated using the active calculator or the formulas at the bottom of the page.

[diagram of PCB layers]

 Where   εr = Relative Dielectric Constant

               W = Width of gap

                 S = Width of track

                 h = Thickness of dielectric

Enter the εr of the PCB: 
Enter the width of the track:  mm
Enter the width of the gap:    mm Effective Dielectric Constant (εeff): 
Enter the thickness of the dielectric:    mm  Characteristic Impedance (Zo):   Ohms
 

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The original formulas are in Transmission Line Design Handbook by Brian C Wadell, Artech House 1991 page 79. The formulas use "a" for the track width and "b" for the sum of the track width plus the gaps either side.

[All formulas for Eeff and Zo calculation]

To avoid microstrip line modes, it is recommended that h >> b and that the component side ground extend away from the track on each side more than "b".

Note: For those who wish to understand how K(k) is found, there is a calculator and equations for Elliptical Integrals of the First Kind.

This calculator is provided free by Chemandy Electronics in order to promote the FLEXI-BOX

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