Far-Field Radar Cross-Section Determination from Near-Field 3-D Synthetic Aperture Imaging with Arbitrary Antenna Scanning Surfaces

*This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible.<div><br></div><div>In this study, we propose a generalized algorithm for far-field radar cross-section determination by using 3-D synthetic aperture imaging with arbitrary antenna scanning surfaces. This method belongs to a class of techniques called image-based near-field-to-far-field transformation. The previous image-based approaches have been formulated based on a specific antenna-scanning trajectory or surface, such as a line, plane, circle, cylinder, and sphere; majority of these approaches consider 2-D radar images to determine the azimuth radar cross-section. We generalize the conventional image-based technique to accommodate an arbitrary antenna-scanning surface and consider a 3-D radar image for radar cross-section prediction in both the azimuth and zenith directions. We validate the proposed algorithm by performing numerical simulations and anechoic chamber measurements.<br></div>

Unified Approach For Multiscale Radar Cross-Section Measurement by Synthetic Aperture Imaging

<div><div>*This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible.</div></div><div><br></div>In this study, we present an improved and unified approach for image-based radar cross-section (RCS) measurement by 2-D synthetic aperture radar (SAR) imaging with an arbitrary curved antenna scanning trajectory. Because RCS is a quantity defined in the far-field distance of an object under test, direct RCS measurement of an electrically large target is often infeasible owing to the spatial limitation of the measurement facility. The method proposed in this study belongs to the class of techniques referred to as the image-based near-field to far-field transformation (NFFFT) to convert the near-field data of scattering experiment into the far-field RCS. In a previous study, we have developed an NFFFT based on 3-D SAR imaging with an arbitrary antenna scanning surface. However, the previous approach is only applicable to the surface scanning which is impossible for a certain case such as measurement using airborne SAR or vehicle-borne SAR. Therefore, one requires an alternative method that can accommodate an arbitrary scanning curve, which is the subject of this study. We derive a generalized correction factor for image-based NFFFT which is designed to ensure the integral transformation in the image reconstruction process be self-consistent for electrically small scatterers. We provide a series of numerical simulations, an indoor experiment, and an airborne SAR experiment to validate that the proposed scheme can be utilized for various situations ranging from near-field to far-field distance.

Unified Approach For Multiscale Radar Cross-Section Measurement by Synthetic Aperture Imaging

<div><div>*This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible.</div></div><div><br></div>In this study, we present an improved and unified approach for image-based radar cross-section (RCS) measurement by 2-D synthetic aperture radar (SAR) imaging with an arbitrary curved antenna scanning trajectory. Because RCS is a quantity defined in the far-field distance of an object under test, direct RCS measurement of an electrically large target is often infeasible owing to the spatial limitation of the measurement facility. The method proposed in this study belongs to the class of techniques referred to as the image-based near-field to far-field transformation (NFFFT) to convert the near-field data of scattering experiment into the far-field RCS. In a previous study, we have developed an NFFFT based on 3-D SAR imaging with an arbitrary antenna scanning surface. However, the previous approach is only applicable to the surface scanning which is impossible for a certain case such as measurement using airborne SAR or vehicle-borne SAR. Therefore, one requires an alternative method that can accommodate an arbitrary scanning curve, which is the subject of this study. We derive a generalized correction factor for image-based NFFFT which is designed to ensure the integral transformation in the image reconstruction process be self-consistent for electrically small scatterers. We provide a series of numerical simulations, an indoor experiment, and an airborne SAR experiment to validate that the proposed scheme can be utilized for various situations ranging from near-field to far-field distance.

Scattering characteristics of surface ships with complex shape

Based on the previously developed by the authors method for estimating the scattering characteristics of objects located near the interface between two half-spaces, the scattering data of a large Project 775 landing ship (NATO codification: Ropucha) are obtained. A surface model of the ship under study and the results of calculations of its scattering characteristics are given. Scattering characteristics were obtained for different probing conditions. The radar cross-section circular diagrams, mean and median radar cross-section values, averaged in different azimuth aspect ranges of probing for the object under study are presented.

Hybrid Deflection of Spoiler Influencing Radar Cross-Section of Tailless Fighter

With the continuous development of advanced fighters towards tailless and flying wing layouts, diverse control surfaces have become the mainstream design. To study the influence of spoiler control surface on the radar cross-section (RCS) of a tailless fighter, a calculation method is presented. The deflection angle of the spoiler is controlled by the fixed mode, linear mode, and smooth mode. The results show that the opening action of the spoiler will break the original stealth characteristics of the aircraft at the key azimuth angles of the head and tail. As the elevation angle increases, this adverse effect will spread to the side. The influence of the different dynamic deflection modes of the spoiler on the aircraft RCS is analyzed. Compared with the linear dynamic deflection mode, the smooth dynamic deflection mode is conducive to the reduction in the average RCS at the given head azimuth. The presented method is effective to study the influence of the spoiler deflection on the electromagnetic scattering characteristics of the tailless aircraft.

Compact Radar Cross-Section Measurement Setup and Performance Evaluation

Radar cross-section measurements require the background reflections to be much lower than the reflections of the device under test. Although, anechoic chambers with special target holders meet this requirement, they are expensive and still have imperfections. To further reduce background reflections or to measure in environments where an anechoic chamber is not suitable, digital signal processing can be used to reduce background reflections. In this paper, a complete signal processing chain realized in Matlab is proposed, involving time gating of the measured target response and a background subtraction technique. Furthermore, the proposed signal processing includes a calibration procedure with either a single known calibration target or multiple known targets to improve measurement uncertainties. A compact measurement setup, consisting of a vector network analyzer and two horn antennas, is used to evaluate the overall performance and the advantages of a multiple known target calibration in a practical manner. The calibrated setup is able to measure the radar cross-section in a frequency range from 2 to 12 GHz with a mean error of less than 0.2 dB for both, VV and HH polarization combinations. It could also be shown, that a multi target calibration can result in an improvement of the measurement uncertainty by about 2.5 %.