Simultaneous Synthesis of Sum and Difference Patterns in Time-Modulated Arrays for Single-Channel Monopulse Tracking

This paper presents a single-channel monopulse tracking method based on the time-modulated array (TMA). In this single radio frequency (RF) channel architecture, the beam steering and simultaneous synthesis of multiple sum (Σ) and difference (Δ) patterns are achieved without multiple independent beamforming networks, thereby improving the simplicity and flexibility of monopulse tracking. The amplitude and phase of the in-phase/quadrature (I/Q) modulation waveform are controlled by digital attenuators and RF switches, respectively. According to this design, the Σ and Δ signals are modulated to harmonic frequencies that are symmetrically distributed around the carrier frequency. Furthermore, to mitigate interference during target tracking, a common weight vector is optimized to suppress the sideband level (SBL) and sidelobe level (SLL). Meanwhile, the harmonic orders of the Σ and Δ patterns are configured flexibly to extend the available bandwidth while accounting for the switching time constraints in hardware implementation. An 8-element array prototype was designed and fabricated to simultaneously synthesize a single Σ-Δ pattern pair using the ±1st harmonics for the single-target tracking experiment, and two Σ-Δ pattern pairs using the ±1st and ±2nd harmonics for the dual-target tracking experiment. The measurement results are in good agreement with the simulation results, thereby validating the effectiveness of the proposed monopulse tracking method.