Design of a Low‐Noise Amplifier With Highly Efficient Sub‐Harmonic Suppression Based on a Self‐Biasing Adaptive Filter for Nonlinear Radar

In nonlinear radar (NLR) systems for detecting concealed electromagnetic devices, effective suppression of the fundamental frequency () and amplification of the second harmonic () are critical for target discrimination. This letter presents a low‐noise amplifier (LNA) architecture with a self‐biasing adaptive filter (SBAF) for NLRs. The proposed LNA selectively suppresses and amplifies through power‐aware control without external bias. The SBAF dynamically adjusts the Q ‐factor of the output resonance circuit depending on the input power level, enabling adaptive suppression of . The circuit architecture comprises four core blocks: a BJT‐based amplifier stage (BAS), a frequency‐selective network (FSN), an adaptive biasing rectifier (ABR), and an active resonance circuit (ARC). A prototype was fabricated and measured at GHz, achieving 54.6 dB suppression at , 14.6 dB gain at , a 9.8 dB improvement in output third‐order intercept point (OIP3), and a noise figure (NF) of 1.4 dB. The proposed architecture demonstrates effectiveness in enhancing nonlinear target detection for NLR applications.