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Abstract In this study, we present an ultra‐wideband full‐duplex system constituted of a wideband 4‐element Vivaldi array and wideband microstrip‐to‐slotline baluns. The proposed system is characterised by its simplicity, high directivity, and high self‐interference cancellation levels over a wide frequency bandwidth. The system is fabricated using basic printed‐circuit board (PCB) technology and can provide at least 50 dB of self‐interference cancellation over the bandwidth of operation, 4–40 GHz, with an average gain of 7.8 dBi. The system has a size of 8 cm × 8 cm × 9.4 cm and can be used as a high data rate link between two distant wireless nodes. To assess the merits of the proposed system and compare it to other published works, a new figure of merit (FoMWFD) dedicated to wide‐band full‐duplex antenna topologies is introduced in this study.