The characteristic impedance (Z_{o}) of a microstrip transmission line can be calculated using the active calculator or the equations at the bottom of the page.

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The following equations were derived from equations 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 ε_{r }and where to use ε_{eff} (although there is a note to use e_{eff} instead of e_{r)}. 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

Where ε_{r} is the Relative Dielectric Constant

W is the Width of track

t is the Thickness of track (1 oz/ft2 = 0.035 mm)

h is the Thickness of dielectric

The above equations are also in *Transmission Line Design Handbook *by Brian C. Wadell, Artech House 1991, with some differences in calculating ε_{eff}. The main equation is attributable to Harold A. Wheeler and was published in, "Transmission-line properties of a strip on a dielectric sheet on a plane", IEEE Tran. Microwave Theory Tech., vol. MTT-25, pp. 631-647, Aug. 1977. The effective dielectric constant equation is from: M. V. Schneider, "Microstrip lines for microwave integrated circuits," Bell Syst Tech. J., vol. 48, pp. 1422-1444, 1969.

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

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