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>

Direct Sampling for Recovering Sound Soft Scatterers from Point Source Measurements

In this paper, we consider the inverse problem of recovering a sound soft scatterer from the measured scattered field. The scattered field is assumed to be induced by a point source on a curve/surface that is known. Here, we propose and analyze new direct sampling methods for this problem. The first method we consider uses a far-field transformation of the near-field data, which allows us to derive explicit bounds in the resolution analysis for the direct sampling method’s imaging functional. Two direct sampling methods are studied, using the far-field transformation. For these imaging functionals, we use the Funk–Hecke identities to study the resolution analysis. We also study a direct sampling method for the case of the given Cauchy data. Numerical examples are given to show the applicability of the new imaging functionals for recovering a sound soft scatterer with full and partial aperture data.

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

In this study, we propose a generalized algorithm for far-field radar cross-section determination from 3-D synthetic aperture imaging with arbitrary antenna scanning surfaces. This method belongs to the class of techniques called image-based near-field to far-field transformation. The previous image-based approaches were formulated based on a specific antenna scanning surface or trajectory such as a line, a plane, a circle, a cylinder, and a sphere--and the majority of them considered 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 demonstrate the proposed algorithm via numerical simulations and anechoic chamber measurements.

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

In this study, we propose a generalized algorithm for far-field radar cross-section determination from 3-D synthetic aperture imaging with arbitrary antenna scanning surfaces. This method belongs to the class of techniques called image-based near-field to far-field transformation. The previous image-based approaches were formulated based on a specific antenna scanning surface or trajectory such as a line, a plane, a circle, a cylinder, and a sphere--and the majority of them considered 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 demonstrate the proposed algorithm via numerical simulations and anechoic chamber measurements.

An enhancement of instruments for solution of general transmission line equations with method of lines, impedance-/admittance and field transformation in combination with finite differences

The Method of Lines (MoL) in combination with impedance-/admittance and field transformation (IAFT) is used to analyze electromagnetic waves. The used cases are wave-guiding structures in microwave technology and optics. The core of the theory is the solution of generalized transmission line equations (GTL). In the case of complex structures, a combination with finite differences (FD) can be used. The quality of this solution essentially depends on the effectiveness of the used interpolation of the differences. The individual steps of the FD are permanently linked to the steps of the fully vectorial impedance-/admittance and/or field transformation, so standard libraries cannot be used. Two approaches based on the linear and quadratic interpolation were built into the impedance-/admittance and field transformation in the past. However, the degree of improvement due to one or another kind of interpolation depends on the concrete behavior of the solution sought. In the case of complex structures, choosing the appropriate type of interpolation should be an effective aid. In this paper, an extension of the family of built-in methods is proposed - with the possibility of being able to build any known numerical method from the class of one-step or multi-step methods into the GTL solution. These can be higher-order methods, including fast explicit methods, or particularly stable implicit methods. The transmission matrices for the impedance-/admittance and field transformation serve as the building site. To illustrate the procedure, some different methods are integrated into the GTL solution. The accuracy of the solutions is tested on selected complex structures and compared with each other and with existing solutions. It is shown that the optimal choice of method and the quality of the solution can depend on concrete structures. Keywords: Method of lines, generalized transmission line equations, impedance/admittance transformation, waveguide structures, finite differences, finite differences with second order accuracy.

EMC Measurement Setup Based on Near-Field Multiprobe System

Multiprobe spherical near-field measurement is a potent tool for fast and accurate characterization of electrical properties of antennas. The use of fast switching in one axis, an azimuth positioner, and a near- to far-field transformation allows a substantial time reduction in antenna measurements while maintaining high-quality results. On the other hand, conventional emissions EMC measurement systems are typically based on detecting the radiated spurious emissions by a device at different frequencies. The systems usually work in far-field (or quasi-far-field conditions), performing the measurements either at 3 or 10 meters. Measurements under these conditions take space and time. Moreover, the systems are not cost-effective for pre-compliance purposes where pre-testing of the device should provide valuable information and confidence about the DUT before performing a compliance test. This chapter analyzes the possibility of cost and space reduction for EMC systems based on multiprobe near-field measurement systems in combination with OTA (over the air measurements), reference-less systems, spherical near-field transformation, phase reconstruction, modal filtering, source reconstruction, and software-defined radio receivers.