The AC resistance of a microstripline and its ground plane

It is found that the RF resistance of a microstripline is substantially higher than the theoretical value from the skin effect of the strip alone. Based on rigorous analysis, it is determined that the extra resistance is caused mainly by the concentration of grounded plane current under a wide microstrip, and the concentration of the strip current toward the ground. It is pointed out that rigorous analytical results can be obtained for the total AC resistance R/sub t/ of a microstripline, since R/sub t/ is the sum of R/sub g/ of the ground plane and R/sub s/ of the strip. The rigorous results indicate that, for wide strips, R/sub g/ approaches R/sub s/, and R/sub s/ can be twice as great as R/sub AC/, the AC resistance of the same strip isolated (i.e. without ground plane). This means that the AC resistance of the microstrip R/sub t/ can be four times as large as the AC resistance R/sub AC/ of the same strip isolated. In turn, R/sub AC/ is larger than R/sub DC/.<>