So far, most of our discussion has concerned RAR, in which the antenna is a physical object that first emits, then collects the radiation. We now turn our attention to the case in which the antenna moves to cover a synthetic aperture (LSA), thus producing SAR. SAR generally refers to the case of a moving radar and a stationary target - usually an extended scene, such as the surface of the Earth; ISAR refers to the case in which the radar is relatively stationary and a rotating target provides all (or most) of the motion to create the synthetic aperture. Obviously, those distinctions are not fundamental, because they depend on the user's coordinate system. Furthermore, the two concepts are not mathematical inverses, and there are gray areas where they merge. This chapter assumes an LFM SAR waveform. It also assumes that the Earth's surface is stationary and (except as noted) flat. For a discussion of SAR imaging of the ocean, which is moving.