Simplified Tapped Delay Line Architecture for Active Cancellation in a 2×2 IBFD MIMO Transceiver

Passive and active cancellation of self-interference (SI) and cross-interference (CI) is examined in an In-Band Full Duplex (IBFD) 2×2 MIMO transceiver. For our system, passive cancellation of the SI and CI is achieved using a combination of a balanced feed network connected to a circularly polarized antenna and a feedforward path connecting the two transceivers. Active cancellation is achieved using a tapped delay line network in a configuration that greatly reduces circuit complexity when compared to other reported systems. Over-the-air measurements of an indoor environment are combined with measured and simulated tapped delay line networks to achieve a total SI cancellation and CI cancellation of 60 dB over 20 MHz.