ABSTRACT
Most engineers, both designers of electromagnetic interference (EMI) devices and others, call EMI black magic. There are four main reasons for this. First, there has not been a well-defined design method. Second, the input and output impedances are not constant over the band of interest. The impedances are usually just good guesses, at best, because the measurements are costly to make and are rarely repeatable. Third, the filter insertion loss test method specifications often confuse or influence the design method. In the 220A specification, requiring 50-ohm source and load impedances, does the filter engineer design the filter for the 50 ohms or for real-world impedances? If the design passes the Military Standard (MIL STD) 220A, 50-ohm, test, what will happen in the real world? Is it the designer’s responsibility to meet the specification or to stop the real-world emissions? Fourth, the design methods outlined in various publications are generally very complex. Most require measurements that are difficult to make and time consuming. Often expensive additional equipment is required to obtain the needed parameters.
