Simultaneous range ambiguity mitigation and sidelobe reduction using orthogonal non-linear frequency modulated (ONLFM) signals for satellite SAR Imaging

Abstract

This letter first attempts to simultaneously reduce range ambiguities and sidelobes in spaceborne synthetic aperture radar (SAR). Two of the limitations of SAR are the range ambiguity phenomenon and the sidelobes effect. The range ambiguity appears with long delayed echoes. The current transmitted signal does not contribute to the reflected echo that is received after the transmission of one or more new pulses. Moreover, the conventional radar commonly uses linear frequency modulated (LFM) waveforms, producing a peak sidelobe ratio (PSLR) of −13.25 dB. Unfortunately, the sidelobes in SAR imagery contribute to speckle and interfere with nearby scatterers. This letter investigates the opportunity of designing the transmitted signals using orthogonal non-linear frequency modulated (ONLFM) waveform. The results demonstrate that ONLFM signals outperform conventional LFM signal. Using the proposed ONLFM waveforms, the PSLR is reduced to −50.25 dB, meanwhile the range ambiguities can be greatly suppressed, despite broadening the mainlobe.