Suppression of the Polarization-Dependent Antenna Carrier Effect in Phased Arrays with Electromagnetic Bandgaps for Airborne SAR Applications

Abstract

The polarization-dependent edge diffraction effects due to the interaction between the antenna and the carrier structure, that enables the antenna mounting on the aircraft, is presented in this paper. The resulting antenna carrier impact is experimentally verified, by means of measurements performed with the operational flight-certified L-band phased array antenna employed in the next-generation DLR bistatic airborne Synthetic Aperture Radar (SAR) sensor. Measured radiation pattern in elevation shows a main beam widening and gain reduction of approximately 1 dB for the vertical polarization, that becomes more sensitive to edge diffraction effects due to the electric field direction and the carrier geometry. On the other side, the performance of the horizontal polarization remains unaffected. In order to achieve a similar radiation response for both polarizations that is required in polarimetric SAR systems, the use of Electromagnetic Bandgaps (EBGs) is proposed. Making use of the surface wave suppression properties of EBGs, the induced currents on the carrier for the vertical polarization can be mitigated, thus reducing the resulting edge diffraction effects without affecting the performance of the horizontal polarization. The presented approach is validated with measurements placing EBGs on each side of the antenna carrier surface. This way, a comparable radiation features for both polarizations can be achieved, that become independent of the carrier structure.