In this paper, the azimuth imaging resolutions of synthetic aperture imaging ladar (SAIL) using the antenna telescopes with a circular aperture for reception and a circular plan or a Gaussian beam for transmitting and with a rectangular aperture for reception and a rectangular plane or an elliptic Gaussian beam for transmitting are investigated. The analytic expressions of impulse response for imaging are achieved. The ideal azimuth spot of resolution and its degradation due to the target deviation from the footprint center, the mismatch from the quadratic phase matched filtering, the finite sampling rate and width are discussed. And the range resolution is also studied. Mathematical criteria are all given. As a conclusion, the telescope of rectangular aperture can provide a rectangular footprint more suitable for the SAIL scanning format, and an optimal design of aperture is thus possible for both a high resolution and a wide scan strip. Moreover, an explanation to the resulted azimuth resolution from our laboratory-scaled SAIL is given to verify the developed theory.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.