Nuclear Hardening and Survivability: Application of Coherent Measurement Techniques to MIL-STD-188-125 Filter Qualification

Electrical points-of-entry (POE) are one of the critical elements which comprise the shielded topology for C4I facilities. The quality of these POEs is critical for the maintenance of low-risk HEMP hardening. Of the POE treatments discussed in MIL-STD-188-125 and MIL-HDBK-423, power and communication/signal-line filters pose a distinct problem. The insertion loss of communication/signal-line filters also are measured per MIL-STD-220 under source- and load-impedances of 50 ohms. The insertion loss of communication/signal-line filters also are measured per MIL-STD-220, except that the measurement is made with a load impedance equal to the image impedance of the filter. In both cases, it is highly unlikely that the filters will have the same insertion loss when they are installed in the C4I facility as the source- and load-impedances seen by the filter will vary widely from 50 ohms and will, most likely, have reactive components. In the worst-case scenario, a filter determined to be compliant after it is tested per MIL-STD-220 may amplify the external stress, thereby degrading the hardness of the facility. Insertion loss with respect to transients is not addressed at the Q/A level. The Phase I technical objective is to extend the coherent-measurement technique to transient excitations by measuring the scattering parameters of the filter under test during the temporal excitation. Power- and signal-line filters also are used in the private sector. The measurement techniques developed in the proposed research effort can easily be adapted by private-sector concerns, particularly the commercial airline industry where filter design is weight/performance critical. Although non-DoD entities do not worry about HEMP stresses on electronics, they are concerned with transient stresses including lightning, ESD, and switching noise.