Investigation of leveling methods in military susceptibility testing: “Leveling under CW signal” and “Leveling under modulated signal”

Abstract

Military radiated susceptibility tests performed in accordance with the RS103 section of the MIL-STD461F standard use a 1 kHz, 50% duty cycle pulse modulation during the dwell time in the exposure period of the Device Under Test (DUT). The military standard requires reaching the target field, alias “leveling”, under the modulation unlike its civil counterpart IEC61000-4-3. In other words, in military testing, the modulation must be activated before starting the leveling process and continued during the entire test. On the other hand, the civil radiated susceptibility test performed as per IEC61000-4-3 requires a leveling period under the continuous wave (CW) signal (CW Leveling), thereafter the required modulation (mostly 1 kHz 80% AM) is applied for exposure. Although the military standard stipulates the activation of the modulation before starting the leveling process and its continuation during the entire leveling process, military tests in practice in many laboratories are performed by first using the leveling with the CW signal, afterwards the modulation during the dwell time like the method used in civil applications, for the sake of ease. Furthermore, many test software solutions designed for EMC susceptibility tests employ the same method also for military radiated susceptibility tests as the modulation after the leveling with the CW signal presents an easier and more comfortable test method than the leveling with modulation. Besides, the leveling with the CW signal does not necessitate the use of pulse factors of measurement devices, so that it saves the laboratory from the burden of taking many factors into account. In this research, we investigated the effects of these two leveling methods in detail and emphasized possible differences in test results which may be caused by them. We also used an actual DUT in order to demonstrate that a DUT may fail during the leveling with the CW signal but may pass the test during the dwell time period with modulation which is the actual period desired by the standard to check the DUT for failure. Finally we make some recommendations about the application of military susceptibility testing methods to awaken EMC laboratories to potential pitfalls of the leveling method performed with the CW signal.