Target micromotion not only plays an important role in target recognition but also leads to esoteric characteristics in synthetic aperture radar(SAR) imaging. This paper finds out an interesting phenomenon, i.e. the angular extent effect, in micromotion target images formulated by the polar format algorithm. A micromotion target takes on multiple pairs of paired echoes(PEs)around the true point, and each PE extends for an angle which is exactly equal to the angular extent of the synthetic aperture,regardless of the micromotion frequency. The effect is derived and interpreted by using the characteristics of Bessel functions. Then it is demonstrated by simulation experiments of a target with different micromotion frequencies. The revelation and interpretation of the effect is highly beneficial to micromotion-target SAR image understanding as well as target recognition. Target micromotion not only plays an important role in target recognition but also leads to esoteric characteristics in synthetic aperture radar (SAR) imaging. This paper finds out an interesting phenomenon, ie the angular extent effect, in micromotion target images formulated by the polar format algorithm . A micromotion target takes on multiple pairs of paired echoes (PEs) around the true point, and each PE extends for an angle which is exactly equal to the angular extent of the synthetic aperture, regardless of the micromotion frequency. The effect is derived and interpreted by using the characteristics of Bessel functions. Then it is demonstrated by simulation experiments of a target with different micromotion frequencies. The revelation and interpretation of the effect is highly beneficial to micromotion-target SAR image understanding as well as target recognition.