Study of the effectiveness of spatially EM-diverse redundant systems under plane-wave illumination

A typical technique within the area of Functional Safety to increase the Safety-Integrity-Level of a safety-critical system is the use of redundancy. However, failures due to Electro-Magnetic disturbances have to be regarded as systematic common-cause failures. When an Electro-Magnetic disturbance is incident on a redundant system with identical paths/hardware, these paths will very likely react in the same way. As a result, no benefit is obtained from the redundant system. To cope with Electro-Magnetic disturbances, Electro-Magnetically diverse redundant systems are needed. This paper studies the effectiveness of spatial diversity to cope with interference caused by strong incident plane waves. Four different geometries are compared: a non-redundant system comprising a single trace on a PCB, a redundant system comprising three parallel traces on a single PCB, a redundant system comprising three non-parallel traces on a single PCB, and a redundant system comprising three differently oriented PCBs. A reciprocity-based technique is used to efficiently calculate the induced voltages and the resulting bit error probability in the different geometries. It is shown that only when using three differently oriented PCBs a significant reduction in the bit error probability is obtained.