Practical analysis on 20H rule for PCB

There are many papers dealing with the 20-H rule, which recommend that the power plane should be shrunk against the ground plane by 20 times of the distance between the planes to realize lower EMI radiation. The effect of the 20-H rule was studied with EM solver using MoM. Bypass capacitors were populated to simulate a realistic printed circuit board (PCB). From the evaluation of the electric and magnetic dipole moment, the contributions of common and differential modes current were calculated. It was found that common mode current in the ground plane was generated when the 20H rule was applied. At the resonance frequencies, the common and differential mode radiations are observed in accordance with its resonance mode, the common mode radiation due to y- or x-directional electric dipole moment for TM01 or TM10 respectively. Considering the common mode current occurrence is a fundamental mechanism of the electromagnetic radiation, it is concluded that the application of the rule increases the radiation.