18.2 Highly-linear integrated magnetic-free circulator-receiver for full-duplex wireless

A fundamental challenge of full-duplex (FD) wireless is the implementation of low-cost, small-form-factor, integrated shared-antenna (ANT) interfaces with low loss, low noise, high TX-RX isolation, and large TX power handling. Providing more TX-RX isolation in the ANT interface that is robust to environmental variations lowers the self-interference cancellation (SIC) and dynamic range required in the RF, analog baseband (BB), and digital domains. Reciprocal shared-ANT interfaces, such as electrical-balance duplexers, fundamentally feature at least 3dB loss (practically >4dB). A non-reciprocal active shared-ANT duplexing scheme was demonstrated, but such active approaches are limited in their maximum supported TX power (-17.3dBm limited by RX compression) and noise performance. An integrated FD RX with a magnetic-free non-reciprocal passive circulator was demonstrated. Despite the circulator's low loss and relatively high linearity, the RX could only handle up to -7dBm TX power due to limited circulator isolation and RX LNA linearity. NF under cancellation was also as high as 10.9dB.