Measurement and modeling of the apparent characteristic impedance of microstrip

Although microstrip has not been incorporated into circuit theory because voltage and current cannot be defined uniquely for it except at zero frequency, microstrip is noted to exhibit an apparent characteristic impedance which is presently denoted 'ZA'. Three methods for the measurement of ZA have been devised and employed in determining three impedance levels of microstrip. The ZA measurements were found to be consistent with the power-current characteristic impedance definition of the approximate longitudinal section electric model of microstrip. Attention is given to simple approximate formulas for the representation of ZA.