In contrast to SAR, the SIREV antenna consists of a physically existent linear array of single elements, which is oriented horizontally and perpendicular to the flight direction as shown in the Figure. The antenna elements may now be switched in sequential order to transmit and receive the radar signals. This monostatic mode with equally located transmit and receive antennas still corresponds to a SAR system, yet we don't have to move a single antenna along a straight trajectory. The disadvantage of the monostatic mode is, that it requires a T/R-module for each antenna element, thereby increasing the complexity and costs of the necessary hardware. A more cost-effective realization may be achieved by using only one transmit antenna, which leads to a bistatic configuration where the receive antennas are spatially separated from the transmit antenna. This configuration can be operated in either a simultaneous or a sequential receive mode. The simultaneous mode makes optimum use of the transmitted signal power by a large effective antenna area whereas the sequential receive mode minimises the hardware requirements. The major disadvantage of the bistatic configuration is, that it reaches only half of the image resolution as compared to the monostatic case. In principle, it is also possible to combine the advantages of the monostatic and bistatic configurations using a small number of transmit antennas.