Source coupling techniques for injection testing of multiconductor cables

Four methods of injecting signals into 30-meter-long 8- and 20-conductor shielded multiconductor cables were investigated to study the coupling effects and to determine which method can best replicate the EMP (electromagnetic pulse) response of the cables. The methods considered were: inductive shield injection, inductive wire injection, direct injection (resistive), and capacitor injection. The injection data were compared with cable data obtained from CW illumination tests. The inductive injectors can produce uniform large wideband shield currents along the length of the cables; the injectors are less affected by nearby objects and are easy to install. Capacitive injectors have disadvantages of poor low-frequency coupling and injector placement, causing out-of-phase, nonuniform shield currents. The direct (resistively) connected injection method had the flattest response but also required connection to the cable shields (which limits this method to shielded cables). Objects near the connecting leads can affect the shield currents at the cable ends