An improved time-frequency phase adjustment technique for ISAR

The time-frequency method is a promising phase adjustment technique for inverse synthetic aperture radar (ISAR). Usually, the time-frequency method estimates the translational Doppler frequency and thus the translational Doppler phase by detecting the peaks of the time-frequency representation at different times. Unfortunately, it has some defects, such as the sensitivity to noise and target scintillation, and the aliasing of the time-frequency representation due to undersampling. In order to remove these limitations, we develop an improved time-frequency method. It estimates the translational Doppler frequency from the envelope correlation of the instantaneous slices of the time-frequency representation. Compared with the traditional time-frequency method, this technique can estimate the translational Doppler frequency more accurately. Moreover, we develop a preprocessing method to avoid the aliasing of the time-frequency representation due to undersampling.