An investigation of microstrip conductor loss

Microstrip conductor loss exhibits complicated behavior that is not generally recognized. Specifically, there are three frequency ranges of interest. At low frequency, current is uniform through the entire cross-section of the line, and the line behaves like a resistor. At medium frequency, the edge singularity forms. In this case, current concentrates on the edge of the line, increasing the resistance. At high frequency, the current splits into two sheets of current, one on top of the line, the other on the bottom of the line. Since microstrip dispersion causes the edge singularity to become larger and current to concentrate on the bottom side as frequency increases, the total resistance increases faster than the normally expected square root of frequency