Radiation and Scattering of EM Waves in Large Plasmas Around Objects in Hypersonic Flight

Hypersonic flight regime is conventionally defined for Mach> 5; in these conditions, the flying object becomes enveloped in a plasma. This plasma is densest in thin surface layers, but in typical situations of interest it impacts electromagnetic wave propagation in an electrically large volume. We address this problem with a hybrid approach. We employ Equivalence Theorem to separate the inhomogeneous plasma region from the surrounding free space via an equivalent (Huygens) surface, and the Eikonal approximation to Maxwell equations in the large inhomogeneous region for obtaining equivalent currents on the separating surface. Then, we obtain the scattered field via (exact) free space radiation of these surface equivalent currents. The method is extensively tested against reference results and then applied to a real-life re-entry vehicle with full 3D plasma computed via Computational Fluid Dynamic (CFD) simulations. We address both scattering (RCS) from the entire vehicle and radiation from the on-board antennas. From our results, significant radio link path losses can be associated with plasma spatial variations (gradients) and collisional losses, to an extent that matches well the usually perceived blackout in crossing layers in cutoff. Furthermore, we find good agreement with existing literature concerning significant alterations of the radar response (RCS) due to the plasma envelope

Radiation and Scattering of EM Waves in Large Plasmas Around Objects in Hypersonic Flight

Hypersonic flight regime is conventionally defined for Mach larger than 5; in these conditions, the flying object becomes enveloped in a plasma. This plasma is densest in thin surface layers, but in typical situations of interest it impacts electromagnetic wave propagation in an electrically large volume. We address this problem with a hybrid approach. We employ Equivalence Theorem to separate the inhomogeneous plasma region from the surrounding free space via an equivalent (Huygens) surface, and the Eikonal approximation to Maxwell equations in the large inhomogeneous region for obtaining equivalent currents on the separating surface. Then, we obtain the scattered field via (exact) free space radiation of these surface equivalent currents. The method is extensively tested against reference results and then applied to a real-life re-entry vehicle with full 3D plasma computed via Computational Fluid Dynamic (CFD) simulations. We address both scattering (RCS) from the entire vehicle and radiation from the on-board antennas. From our results, significant radio link path losses can be associated with plasma spatial variations (gradients) and collisional losses, to an extent that matches well the usually perceived blackout in crossing layers in cutoff. Furthermore, we find good agreement with existing literature concerning significant alterations of the radar response (RCS) due to the plasma envelope

Optimization of a Compact Frequency- and Environment-Reconfigurable Antenna

This paper presents a novel ultra-compact (0.17 x 0.17 x 0.05 wavelengths) reconfigurable antenna equipped with shunt switches at the edges of the radiating elements; in addition to wide-band frequency-reconfigurability, the antenna can also adapt to different environments. The challenging task of designing a compact antenna for multi-band and multi-environment operation is tackled by a hierarchical optimization process consisting of the genetic algorithm (GA) and local search for geometry optimization, and exhaustive search for computation of the optimum switch patterns for a fixed geometry. Both tunability and environment robustness were confirmed in simulation and measurements on a proof-of-concept prototype where switches were simulated by soldering. Numerical analysis of the impact of commercial MEMS devices is also reported, including a case study of practical interest: a compact antenna that can operate at different locations around a simplified model of a laptop PC without performance degradation

Comparative investigation of methods to reduce truncation errors in partial spherical near-field antenna measurements

This paper presents a comparative investigation of two different but highly suitable techniques for the accurate determination of the full sphere pattern of an antenna from truncated spherical near field measurements. The first approach is based on an iterative procedure which exploits the band-limitedness properties of the radiated field to correctly reconstruct the full sphere data [1]. The second approach was first described in [2] and is based on determining a set of equivalent currents that radiate the same pattern in the known area and thus extrapolate the unknown fields in the truncated area. The comparative study is performed on actual measured near-field data to investigate the effectiveness of each technique in realistic spherical near field antenna measurement scenarios. © 2012 IEEE

Full-Wave Electromagnetic Optimisation of Corrugated Metallic Reflectors Using a Multigrid Approach

Abstract A multigrid optimisation strategy is introduced to design passive metallic reflectors with corrugated shapes. The strategy is based on using genetic algorithms at multiple grids and shaping the metal sheets, starting from coarse details to fine tunings. This corresponds to a systematic expansion of the related optimisation space, which is explored more efficiently in comparison to a brute-force optimisation without using grid. By employing the multilevel fast multipole algorithm to analyse the electromagnetic problems corresponding to optimisation trials, we obtain accurately designed reflectors that provide focussing abilities with very high performances at single and multiple locations. The designed reflectors are also resistant to fabrication errors with less complex corrugations and simplified reflection mechanisms compared to those found by no-grid optimisation trials