Asymptotic and full wave simulation models for compensated compact range design and analysis

Compensated compact ranges (CCR) can be considered a standard for real-time and high accuracy measurements for spacecraft antenna and payload testing. A compact range is an indoor antenna test facility which consists mainly of a large antenna reflector (single, dual, or even multiple reflector arrangements are possible) which is illuminated by an appropriate feed system and reflected via the reflector(s) into a test zone area, the so-called quiet zone (QZ). This test zone is located close to the reflector in order to utilize the radiated near-field distribution characteristic. The interesting fact is that this near-field zone shows a similar behavior in a limited area as it would be at the classical far-field distance. Since the reflector size is finite the reflector edges produce diffracted field contributions which are undesirable at the quiet zone. In order to predict the performance of the quiet zone numerical simulations are required and mandatory for a state-ofthe-art facility. Available appropriate electromagnetic field solvers can be distinguished between (a) full wave and (b) asymptotic methods. Full wave techniques for the computation of scattered and diffracted electromagnetic fields are computationally intensive and traditionally impractical to handle for CCR design. Due to this fact, asymptotic methods have been traditionally used during the design of such facilities. These methods offer acceptable accuracy to solve scattering problems at short wavelengths but their precision becomes more than questionable for objects which size is comparable to the wavelength. Astrium´s CCR dimensions are typically of several hundreds of lambdas at higher frequencies. In the past decade, significant advances related to CPU/memory costs reduction, parallel computation, and new formulations based on Multilevel Fast Multipole Methods allow full-wave calculations for increasing frequencies. This enables verification of asymptotic methods by comparison with full wave calc- lations.