Phase error compensation method using polynomial model for a direct digital synthesizer based chirp signal generator

Abstract

As an imaging radar, synthetic aperture radar (SAR) requires the images of high-resolution. To enhance the resolution of images, SAR adopts the chirp signal [1]. The chirp signal is often referred as a linear frequency modulated (LFM) signal because the instantaneous frequency of chirp signal increases or decreases linearly with the time. To realize the chirp signal in SAR system, the chirp signal generator adopts the direct digital synthesizer (DDS) type arbitrary waveform generator. However, the phase error due to the truncation in DDS degrades spectrum purity of output signal. This paper proposes the phase error compensation method for DDS chirp signal generator using polynomial model. To verify the performance of proposed method, the peak to side-lobe ratio (PSLR) and integrated side-lobe ratio (ISLR) are analyzed. In this paper, compared to the conventional DDS system, the PSLR is improved from −13.5536 dB to −13.6207 dB and ISLR is improved from −10.3263 dB to −10.3126 dB when the proposed method is applied.