Since the occupation density of microwave frequency band is highly increased, the electromagnetic environment is getting more severe. It is sometimes reported that electronic machines are not normally operated because of the influence of undesired electromagnetic wave. It often gives fatal blow to even human life and thus becomes serious social problems. Specially, we increasingly spend much time working in front of PC. So, EMC problem for personal computer is very important nowadays.
In this thesis, the noise source was searched for minimizing interference of the inside PC. The shape of the main board with extension card which is like a reflector. The form of the main board and the extension card may occur the radiation noise at surroundings because it is a function of a reflection plate. So the conventional model and the proposed one in this thesis are compared after measuring.
The radiation noises were measured, compared, and analyzed for the three cases : the extension card is not fitted with case, card is fitted with case, and two cards are fitted with case.
The difference of radiation noise between the two cases, one of which is one extension card fitted with and the other is two cards fitted with, was about 2 ~ 3 dB, and the difference of radiation noise between one card with a slot and each two card with a slot is about 2 ~ 3 dB. Moreover, the difference between the cases of no card and of the fitted with a extension card is about 20 dB. So, main board fitted with extension card showed worse radiation noise than the cases of no card.
As a result, it is very important not to make the form of the fitted with a extension card in order to reduce radiation noise. It is careful to make the form of the right angle to another devices.