Wideband RF Self-Interference Cancellation With Three Taps Using Trigonometric Frequency-Domain Padding Method

This paper proposes a novel RF interference cancellation method based on Fourier analysis and enhanced by trigonometric frequency-domain padding to enable active cancellation in in-band full duplex radio front-ends. Active cancellation uses a multi-tap RF canceller to mimic the self-interference (SI). The SI within the target bandwidth is first characterized using Fourier analysis. Based on this analysis, a tap implementation strategy is proposed. To achieve the desired SI cancellation (SIC) performance with three taps, at least one tap should be implemented with the dominant delay path. Additionally, the other taps should be spaced uniformly in delay, including the dominant delay path. However, this approach introduces a band-edge overshooting problem, narrowing the bandwidth. To address this issue, this paper introduces a trigonometric frequency-domain padding method. By applying Fourier analysis to this padded SI, the proposed method effectively mitigates the band-edge overshooting problem. An RF canceller is also introduced, featuring a group delay controller to implement the dominant delay path and fixed delays to maintain uniform delay intervals between taps. Consequently, the proposed method achieves a total 60-dB SIC without band-edge overshooting over the wide bandwidth of 3.6–3.7 GHz.