Performance degradation due to coupling between high-speed traces and on-board antennas

Self-interference between digital interfaces and onboard wireless modules and antennas is rapidly becoming a major problem for Printed Circuit Board engineers. In this paper, the severity of on-board self-interference is quantified. Two working conditions are considered. First, the situation is considered in which the antenna is in receive mode. As the incoming (signal) fields are most often rather low, only small (signal) voltages are induced at the antenna port. It is shown with a simple example that the level of the noise voltage induced at the antenna port due to the switching of digital interfaces can be significant compared to the signal voltage, thereby leading to a low Signal-to-Noise Ratio. Second, the situation is considered in which the antenna is in transmit mode. As the power radiated by the on-board antenna can be quite large (e.g. typically 2 Watt for GSM), the signal voltages at the antenna port can be quite large. With the same simple example, it is shown that this leads to a significant noise signal at the digital interfaces, thereby increasing the Bit Error Rate.