Impedance Calculator for Microstrip

The structure of a Microstrip is shown below. Impedance calculators attempt to calculate the characteristic impedance and the capacitance per unit length as a function of width of trace W, height above ground plane H, permeability of dielectric and thickness of trace t.



That IPC formula for microstrip are given by,



These formulas work very well when the trace width is not too wide as compared to its separation from the ground place. These formula were designed for practical PCBs and therefore work well when the value of the characteristic impedance in close to 50 Ohms.

Online calculators or spreadsheets can be used to calculate impedance and capacitance per unit length.

Wadell’s formula provides a better accuracy over the IPC formula under certain conditions. It calculates effective dielectric constant and the effective trace width and then calculates impedance.



The following table lists the comparison of the impedance calculator using hspice calculator with respect to the IPC formula and the Wadell formula.



It is clear from the table that the Wadell formula is more accurate in this particular case and can be used in most of the cases, in case of microstrip. The IPC formula is accurate in ranges near practical PCB configurations.

Online calculators are available and can be used to calculate impedance using the Wadell formula.
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