Do you remember 20H Rules? 是否还记得20H原则

As the operating frequency of electronic circuits continues to increase, today’s package and printed circuit board designers face more radiation problem than ever before. The control of radiated emissions to make the package comply with radiation constraints is one of the most important aspects of the EMC study. Some “rules-of-thumb” are employed to help the designers to reduce the radiation problems. This paper presents an investigation on the effects of the 20-H rule and the shielding vias on radiation from printed circuit boards.


The 20-H rule states that the ground planes are extended beyond the power planes by about 20 times the distance between the planes. Let us consider the simple structure consisting of one power plane and one ground plane.




It can be seen that the larger the separation between planes, the smaller the amplitude of the reflections coefficient and the larger the radiation. The reflection coefficient of the 20-H rule structure can be estimated by that of the power plane.


Because the separation between the power plane and its image plane is twicethe reflection coefficient of the 20-H rule structure is smaller in the

amplitude. Therefore, more radiation is expected to come out of the edges of the board implemented with 20-H rule.