Parallel Wire Susceptibility Testing for Signal Lines

A technique is presented which can be utilized to establish a standardized procedure for performing conducted susceptibility testing on signal lines at the component and/or the subsystem level. Typical military specifications require that the test function be injected to the test lines via a susceptibility transformer, a coupling capacitor, or a standardized network, such as the line stabilization network (LSN). Although these methods may be adequate for testing of power line susceptibility, they present several disadvantages when utilized in signal lines, such as impedance loading, the requirement for physical insertion, and proximity to the load. These disadvantages become more pronounced at RF where the signal developed across the input of the test specimen may be considerably lower than the signal injected at the physical insertion point. A technique that overcomes these deficiencies utilizes a coupling jig that 1) does not require a physical connection, and 2) provides a known coupling across the input impedance of the package being tested-thus simulating, in a very realistic manner, interference coupling as it may occur in a system. A general expression for coupling prediction and a computer solution for various values of load impedances are presented.