Design of an Airborne Dual-Polarized Triple Stacked Patch Antenna for Broadband SAR Applications in P-Band

E-SAR is the DLR multi-frequency experimental airborne SAR system. Five different frequency bands from P- to X-band are established. General applications are measurements of tree height, biomass estimation, land use and land cover classification. P-band has a high ground penetrating capability and is a matter of particular interest for geoscience. Up till now the centre frequency of the P-band system was 450 MHz with a maximum bandwidth of 60MHz. To improve system performance the centre frequency is shifted to 350MHz and the maximum system bandwidth is extended to 100MHz. The design of a dual-polarised aperture-coupled triple stacked patch microstrip antenna for airborne SAR-systems, working at P-band, is presented. A bandwidth of 28% is achieved at a low level of cross polarisation with a centre frequency of 350MHz. The main beam of the passive array antenna points to an angle of 37° degree (off-nadir). Physical key parameters are discussed depending mechanical boundary conditions like maximum weight and dimensions. Single antenna element structure for wide band operation and the orientation of the elements in the antenna group is shown. Another aspect is the passive phase shifting network and amplitude steering in a small array antenna with high coupling effects between the elements. Measurements of the reflection coefficient and far field pattern of the P-band array are shown. Finally some aspects of attaching the antenna to a small turboprop aircraft are presented.