Distant Sidelobe Suppression for Multi-Timeslot Wide-Gap Frequency-Hopping RFPA Radar

Random frequency and pulse repetition interval agile (RFPA) signal has been gaining popularity in radar systems, owing to its low probability of intercept and anti-jamming capability. However, one limiting factor that hinders its application is the presence of distant sidelobes widely distributed along the range dimension. Recently, we have proposed a multi-timeslot wide-gap frequency-hopping sequence (WGFHS) to suppress these distant sidelobes. Nevertheless, a frequency-domain analysis shows that its performance is limited by the energy leakage among echoes generated by multiple adjacent pulses. Inspired by the problem of adjacent channel interference (ACI) mitigation in wireless communications, we propose a distant sidelobe suppression framework via selective out-of-subband (OOSB) energy leakage reduction, in which the energy of each transmitted pulse leaked to the subbands of its multiple adjacent pulses is reduced. A realization of this framework based on intrapulse phase coding is presented, where an optimization problem is formulated by taking advantage of the property of the selective set of subbands. This problem is then solved with the coordinate descent method. Simulation results show that the proposed framework and its realization efficiently suppress the residual distant sidelobes of multi-timeslot wide-gap frequency-hopping RFPA radars, and significantly improve the performance of detecting weak targets in scenes with mixed strong and weak targets as well as scenes with strong clutter in particular.