Modern Development Processes of Antennas for Polarimetric and Interferometric Airborne Synthetic Aperture Radar

Abstract

Antennas for polarimetric and interferometric airborne Synthetic Aperture Radar (SAR) underly strict requirements in terms of the radiation characteristics itself and on the special environmental conditions. While we require a homogenous illumination of the target area in both orthogonal polarizations, nadir echo suppression, wide bandwidth and a high suppression of sidelobes, on the other side we have to face the limitations of the aircraft. Size, weight and interferences from the mounting structure are just a few restrictions to name. During the challenging antenna development in frequency ranges between 300 MHz and 38 GHz we are using modern tools and technologies. Beginning with the simulation setup, a solely Finite Element Method (FEM) solver is mostly not sufficient. Experience has shown that especially for interferometric applications the antenna carrier must be included in the simulation to ensure sufficient uncoupling and to avoid multipath reflections. To include also the antenna carrier of size >10 1000 wavelengths, often hybrid simulations are conducted which combine FEM and Integral Equation (IE) methods within the same setup. Also, modern measurement possibilities like 3D laser scans, thermal camera and antenna test ranges are part of the prototype development. Another particular strength is the direct implementation of antenna measurement results at different interfaces of the simulation tools. This allows for adaptive developments up to the final design. Even modern manufacturing methods like additive manufacturing of antennas find application in our laboratories. A special technology for microstrip feeding networks are resistive films like Ticer and Ohmega foils, which avoid soldering of ohmic resistors. Via this process the resistors are directly etched into the substrate during the circuit board manufacturing process – at costs of power handling. Here, you can see a part of our DuoLim feeding network. In the meantime, the gained experience during these developments finds application in many other fields: we support other departments and external customers with antenna and random developments for ground-based and space missions, radar cross section verifications or optimized antenna placement.