The multi-input / multi-output (MIMO) principle is well known for communication applications, whereas at least the name "MIMO" is relatively new for the radar application. There are a couple of papers addressing MIMO-radar, whereas the use of the MIMO-principle to SAR and/or MTI applications is rarely investigated. In this paper, the special configuration of an along-track MIMO antenna for SAR/MTI is treated. This configuration is axial symmetric with respect to the relative phases which leads to independence on the elevation height, making the derivations simpler. We will derive properties of an along-track MIMO array, present performance measures and processing schemes for a future MIMO-SAR system.