An Analysis of an Electrical Balanced Full Duplex RF Front-End Self-Interference Cancellation Implementation Accuracies and Their Impact on the Isolation-Bandwidth Integral

This paper analyzes the effects of the accuracy of self-interference cancellation (SIC) load-balance circuits in electrical-balanced RF front-ends intended for simultaneous transmit-receive (STR) applications. We compare accurate versus approximated SIC transfer functions, analyze balancer amplitude and phase inaccuracies, and demonstrate that the total pre-SIC TX leakage influences the achieved post-SIC TX-RX isolation. Additionally, we review the performance of a Chebyshev balancer and examine the impact of inaccurate inductors and capacitors on the SIC performance. We implement an un-tuned filter on a PCB to evaluate the circuit inaccuracies' effect on SIC performance. Simulation results indicate over 30 dB isolation across 400 MHz for an RF front-end with a 7 dB return loss antenna, around 2.65 GHz, and the measured design shows 26dB over 240 MHz. Our findings suggest a tuned design with an adequate resolution for the transfer function of the TX leakage and the targeted SIC.