A major part of electromagnetic radiation from any shielded circuit is due to the apertures provided for cooling, air ventilation and access to the circuits. As we know electromagnetic interference of a system can decrease the efficiency of a system itself or other systems. From Electromagnetic compatibility point of view, the analysis of these impacts will result in better and more efficient system design. In this book the application of different hybrid methods for analysis the interference in high frequency shielded and unshielded circuits have been discussed.