![[diagram of PCB layers]](../images/microstrip-drawing.gif)
Where εr= Relative Dielectric ConstantW = Width of track
t = Thickness of track (1 oz/ft2 = 0.035 mm)
h = Thickness of dielectric
The characteristic impedance (Zo) of a microstrip transmission line can be calculated using the active calculator or the formulas at the bottom of the page.
Where εr= Relative Dielectric Constant
W = Width of track
t = Thickness of track
(1 oz/ft2 = 0.035 mm)
h = Thickness of dielectric
The following formulas where derived from formulas used in an article by Rick Hartley http://www.jlab.org/accel/eecad/pdf/050rfdesign.pdf. It is not too clear from the article by Rick Hartley where to use εr and where to use εeff (although there is a note to use eeff instead of er). The substitutions selected give results that are almost identical to the "benchmarks" in http://www.polarinstruments.com/support/cits/IPC1999.pdf, and these benchmarks were obtained by numerical methods. The accuracy of results obtained from this calculator can be checked by making a sample PCB and measuring the resulting impedance. Guidance for this can be found at Measuring Characteristic Impedance of PCB tracks using a Vector Network Analyser.
![[calculation formula]](../images/microstrip-formula2.gif)
![[Microstrip formula]](../images/microstrip-formula1.gif)
The original formulas are in Transmission Line Design Handbook by Brian C Wadell, Artech House 1991 and these in turn are mainly attributable to Harold Wheeler.
This calculator is provided free by Chemandy Electronics in order to promote the FLEXI-BOX
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