*The Present Situation and Development for Spaceborne Synthetic Aperture Radar Antenna… DOI: http://dx.doi.org/10.5772/intechopen.106040*

Early spaceborne SAR systems, such as SeaSat in 1978 and SIR-C in 1981, used a single polarimetric antenna. In recent years, as more and more spaceborne SAR systems have the ability of full polarimetric signal processing, there is an urgent need for the full polarimetric performance of SAR Antenna. At present, there are two main types of spaceborne SAR antenna: microstrip patch array antenna and waveguide slot array antenna. The former, represented by COSMO-Skymed in **Figure 5** [7] and Radarsat-2 [6], is usually a double-layer microstrip patch array based on lightweight dielectric materials [16, 17]. It has the advantages of light structure weight, dualpolarization, flexible arrangement of elements and subarrays, etc., but it has a slightly larger loss compared with the other scheme. The latter is represented by TerraSAR-X [18] and sentinel-1 in **Figure 6** [19, 20]. The ridged waveguide wide-edge slot antenna [21] and the reduced waveguide narrow-edge slot antenna made of carbon fiber reinforced plastic [22, 23] are alternately arranged to form a dual polarimetric array antenna, which has low loss and high radiation efficiency, but it is slightly heavy, difficult to design as well as process and difficult to adjust the position of array elements and subarrays.

• Limited range scanning angle and small azimuth scanning angle

The orbit altitude of spaceborne SAR platform is usually between 500 and 800 km. Due to the limitations of earth curvature and range resolution, the antenna beam in the range direction, that is, the direction on the elevation plane, is usually within the range of 15°–50° starting from the connecting line between the satellite and the nadir on the earth's surface, with a span of 35°. Limited by the Doppler bandwidth of the processed echo signal, the beam coverage and scanning range in the azimuth, that is, horizontal plane, are usually within 2° [5, 7, 17]. Compared with the phased array

**Figure 5.** *Photo of microstrip patch array SAR antenna of COSMO-Skymed.*

**Figure 6.** *Photo of waveguide slot array SAR antenna of Sentinel-1.*

antenna of other applications, such as warning/fire control radar, the scanning range of spaceborne SAR antenna is limited in range and very small in the azimuth.
