New Dimensions in Measuring Filter Insertion Loss

The MIL-STD-220A 50-ohm resistive method of measuring filter insertion loss using buffer networks has successfully masked the deficiencies of filters for many years. The method of measuring filter insertion loss proposed herein overcomes all the shortcomings of previous standards. It can measure insertion loss with full-rated line currents flowing (up to 400 amperes), without being adversely affected by the heavy currents and without affecting the performance of the system. It can be clamped around filter lines at installations without disturbing the circuits under test and thus can measure filter performance working into realistic load and source impedances. Filters can be evaluated using load and source impendance conditions selected as preferred from tenths of an ohm, to conjugate matched, to complex-resistive-reactive combinations, and to 50 ohms as desired. Any type of filter can be tested from lumped element to absorptive, active, or ceramic. Of major importance is the fact that this technique can also evaluate in the passband where filter insertion loss and gain is of great interest. These advantages are combined in a system that is capable of completing measurements quickly.