Application of a Finite-Volume Time-Domain Technique to Three-Dimensional Objects

Concurrent engineering approaches for the disciplines of computational fluid dynamics (CFD) and electromagnetics (CEM) are necessary for designing future high-performance aircraft. A characteristic-based finite-volume time-domain (FVTD) computational algorithm, used by CFD and now applied toCEM, is implemented to analyze the radar cross section (RCS) of the ogive and cone-sphere. The technique utilizes a scattered-field formulation of the time-dependent Maxwell equations. The FVTD formulation implements a monotone upstream-centered scheme for conservation laws for the flux evaluation and a Runge-Kutta multi-stage scheme for the time integration. The results are obtained from the electromagnetic fields via a Fourier transform and a near-to-far field transformation

The Calibration of Bistatic Radar Cross Section Measurements

Recent advances in signal processing and remote sensing have highlighted the importance of bistatic radar systems for the purposes of environmental monitoring, surveillance, and tracking radar. The calibration of such systems has been problematic-much more so than similar monostatic systems, primarily as a result of the lack of reference objects suitable for calibrating at any given bistatic angle. This research deals with the problems of calibrating full-polarimetric laboratory-environment bistatic radar systems, including the lack of suitable calibration targets and procedures, and operational considerations such as alignment and mounting. Several popular bistatic calibration techniques are classified, evaluated, and comparisons are made between the relative merits of various calibration objects. The analysis addresses sensitivity to target alignment error, sensitivity to polarization impurity, and ease of implementation. Both theoretical concepts and practical considerations are discussed, based on measurements accomplished at the European Microwave Signature Laboratory (EMSL) of the Joint Research Center (JRC) in Ispra, Italy. Significant gains in co-polarized channel accuracy and cross-polarization purity are realized with calibrations that utilize the complete system distortion model and these conclusions are discussed in detail

Forward scatter radar for air surveillance: Characterizing the target-receiver transition from far-field to near-field regions

A generalized electromagnetic model is presented in order to predict the response of forward scatter radar (FSR) systems for air-target surveillance applications in both far-field and near-field conditions. The relevant scattering problem is tackled by developing the Helmholtz-Kirchhoff formula and Babinet's principle to express the scattered and the total fields in typical FSR configurations. To fix the distinctive features of this class of problems, our approach is applied here to metallic targets with canonical rectangular shapes illuminated by a plane wave, but the model can straightforwardly be used to account for more general scenarios. By exploiting suitable approximations, a simple analytical formulation is derived allowing us to efficiently describe the characteristics of the FSR response for a target transitioning with respect to the receiver from far-field to near-field regions. The effects of different target electrical sizes and detection distances on the received signal, as well as the impact of the trajectory of the moving object, are evaluated and discussed. All of the results are shown in terms of quantities normalized to the wavelength and can be generalized to different configurations once the carrier frequency of the FSR system is set. The range of validity of the proposed closed-form approach has been checked by means of numerical analyses, involving comparisons also with a customized implementation of a full-wave commercial CAD tool. The outcomes of this study can pave the way for significant extensions on the applicability of the FSR technique

Bistatic and Multistatic Radar Systems

Radar systems, based on bistatic radar concept attracted a substantial attention in the recent years. Passive coherent location systems using \"transmitters of opportunity\" like radio or TV broadcasters, GSM base stations, satellite communication and GNSS signals proved their potential in detection and tracking moving targets over a significant area. In this paper the multistatic location system with non-cooperative transmitters is described and various aspects of signal processing and signal parameters are discussed

Numerical methods for electromagnetic engineering: Class Notes

Full classnotes2022/20231r quadrimestre3.

Development and Evaluation of a Multistatic Ultrawideband Random Noise Radar

This research studies the AFIT noise network (NoNET) radar node design and the feasibility in processing the bistatic channel information of a cluster of widely distributed noise radar nodes. A system characterization is used to predict theoretical localization performance metrics. Design and integration of a distributed and central signal and data processing architecture enables the Matlab®-driven signal data acquisition, digital processing and multi-sensor image fusion. Experimental evaluation of the monostatic localization performance reveals its range measurement error standard deviation is 4.8 cm with a range resolution of 87.2(±5.9) cm. The 16-channel multistatic solution results in a 2-dimensional localization error of 7.7(±3.1) cm and a comparative analysis is performed against the netted monostatic solution. Results show that active sensing with a low probability of intercept (LPI) multistatic radar, like the NoNET, is capable of producing sub-meter accuracy and near meter-resolution imagery

Design and Analysis of Ultra-Wideband Split Transmit Virtual Aperture Array for Through-the-Wall Imaging

The concept of virtual aperture and the point spread function for designing and characterizing ultra-wideband near-field multiple-input multiple-output active imaging array are investigated. Combining the approach of virtual aperture desynthesis with the monostatic-to-bistatic equivalence theorem, a kind of linear UWB MIMO array, the split transmit virtual aperture (STVA) array, was designed for through-the-wall imaging. Given the virtual aperture, the STVA array is the shortest in physical aperture length. The imaging performance of the designed STVA array in the near field is fully analyzed through both numerical and measured data. The designed STVA array has been successfully applied to imaging moving targets inside buildings

Bistatic sonar and a novel form of variable depth sonar

This thesis relates to the sonar system research undertaken for a Naval Requirement for proposals to improve the cost effectiveness of the defence of shipping against submarine attacks. Defence systems evolved as a function of the developing technology of the opposition which in this instance is the ability of a submarine to remain undetected below the sea surface while searching for, tracking and attacking its targets. An inherent problem for underwater detection with Escort Ships hull type sonars is its location on the air-sea interface with the need of a two-way propagation path to access the depth-range volume available to a submarine. As the power of an Escort's sonar is increased so is the size of ship, 5000 tons and more, to accommodate the optimum size of transducers required.Sonar system research at all times is a multi-discipline task and in this particular case was further broadened with a requirement to review the possibilities for sources of energy other than underwater acoustics. The research confirms the dominance of sonar for underwater detection and establishes the feasibility of a Bistatic Sonar concept which replaces the two-way propagation path of a hull type sonar with a one-way path, source-target-receiver with a variable depth directive towed line receiver on a small ship as a distant receiver. A second objective which became feasible with the development of an adequate towed source was a variable depth sonar which has now been produced by British Aerospace for a world market. A summary of the thesis is provided as an introduction to the subject matter of the different sections

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

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