Analysis on spectral regrowth of chirp bandwidth expansion technique in high‐resolution SAR system

This article presents an analysis of the root causes of the spectral regrowth due to the higher‐order intermodulation in a chirp bandwidth expansion scheme using a single‐sideband modulator and frequency multipliers. The spectral regrowth of synthetic aperture radar waveform was reduced by minimizing the gain and phase imbalances between the I and the Q channels. Further, the gain and phase imbalance requirements were defined on the basis of the evaluation of the impulse response function. The 150‐MHz bandwidth of a chirp signal at 2.4 GHz was expanded to 600 MHz at 9.6 GHz. By adjusting the dc offset and the gain imbalance between the I and the Q channels, the carrier level was reduced from −28.7 to −53.4 dBm and the sidelobe levels caused by the spectral regrowth were reduced by approximately 8–9 dB. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:400–404, 2014