Frequency-Independent Analog Interference Cancellation with Adaptive Phase Control for Narrowband Receivers

Reliable signal detection in narrowband communication receivers becomes challenging under strong electromagnetic interference. This study presents a frequency-independent, algorithm-supported analog interference cancellation architecture designed to suppress strong interference signals in narrowband (channel bandwidths of up to 25 kHz) communication receivers such as public safety, industrial, and maritime receivers. In the proposed structure, interference cancellation is performed at an intermediate frequency (IF) of 44 MHz, independent of the signal frequency. The received signals are downconverted to the specified IF by a front-end circuit, thereby enabling the use of the same analog cancellation architecture at different operating frequencies. Operating at a fixed narrowband IF enables interference suppression to be performed using a single phase shifter in the cancellation circuit without requiring multiple taps. The phase optimization is continuously adjusted by the adaptive perturbation algorithm implemented on the FPGA to determine the operating point at which the total output power is minimized and the interference is suppressed. The developed system, customized for VHF narrowband receivers, has been tested in a laboratory environment under known and unknown interference scenarios. Measurement results demonstrate that the proposed architecture provides 54 dB of interference cancellation performance and successfully maintains communication continuity while preserving the desired message signal. The results confirm that the proposed architecture offers an effective and practical solution for frequency-independent and real-time analog interference cancellation in VHF communication systems.