Ohio State University ElectroScience Laboratory Research Articles

Radar images of penetrable targets generated from ramp profile functions

Images can be generated for penetrable targets from their scattered fields when the time dependence of the incident electromagnetic (EM) wave takes the form of a ramp function. Previous researchers have developed these concepts for conducting targets. This paper focuses attention on penetrable targets. Ramp response signatures of the targets for cases where the dielectric constant of the target is greater than and also less than that of the ambient medium are included. The latter case can be applied as a signature of antipersonnel mines. The results contained herein are based on: (1) scattering measurements in The Ohio State University ElectroScience Laboratory compact range; (2) scattering computation using an eigenfunction solution and a method of moments solution; and (3) a very limited set of measurements generated from a buried land mine using the ElectroScience Laboratory ground penetrating radar. The targets presented in this paper include metallic and dielectric spheres and actual land mines.

High resolution Ka-band images of a small tree: measurements and models

Ka-band (27 GHz to 36 GHz) radar images of a 2.5-m red maple tree, measured in the Ohio State University ElectroScience Laboratory (ESL), Columbus, compact range, are presented. Radar images of the tree with and without leaves were obtained, as well as images of a 6 in diameter metal sphere obscured by the tree for investigation of attenuation effects. The large bandwidth (9 GHz) of these measurements provides a cm scale range resolution, so that backscatter from individual components of the tree canopy can be separated. In addition, measurements made as a function of azimuth angle in 0.1 degree steps allow inverse synthetic aperture radar (ISAR) images to be obtained with cm scale resolutions in down and cross range. A single scattering model, in which tree branches are represented as a deterministic collection of cylinders and leaves as a distributed collection of curved dielectric sheets, is combined with a detailed measurement of the tree geometry to provide theoretical ISAR images for comparison with the measured data. Although incomplete knowledge of tree geometry limits a direct quantitative comparison of the measured and modeled returns, a qualitative comparison of images shows that single scattering models may be sufficient for obtaining many features of foliage objects in Ka-band radar images.

SAR processing of ground-penetrating radar data for buried UXO detection: results from a surface-based system

Battelle and The Ohio State University ElectroScience Laboratory have built and demonstrated a ground-penetrating radar (GPR) system for locating buried unexploded ordnance (UXO), the system is ground based and towed by an autonomously controlled vehicle as part of the subsurface ordnance characterization system (SOCS). This paper presents the results of the synthetic aperture radar (SAR) processing of the radar data acquired at Tyndall Air Force Base, FL, and Jefferson Proving Ground (JPG), IN.

New polarimetric calibration technique using a single calibration dihedral

A new polarimetric RCS calibration technique using a dihedral corner reflector as the single calibration target is presented. This scheme is valid for any monostatic or quasi-monostatic radar system and characterised by five aspects: (a) scattering matrix measurements of only a single calibration dihedral at two orientations are needed; (ii) the radiation polarisation effect and the four measurement channels are separated in this new model; (iii) the frequency responses of four measurement channels are modelled as mutually independent and thus, no special care has to be taken for signal paths and nonreciprocal properties in a measurement system; (iv) the calibration procedure is simplified by taking advantage of small cross-polarised terms and no complicated matrix algebra is involved; (v) the calibrated results are valid for wideband applications because no assumptions are made relative to the theoretical solution for the calibration dihedral. This technique has been verified by several 2-18 GHz wideband RCS measurements using various feeds in the compact range at the Ohio State University ElectroScience Laboratory. Based on these measurements, an effective polarisation isolation close to -60 dB has been demonstrated.

Critical range evaluation using a diagonal flat plate

A novel technique is presented to image stray signals in RCS measurement ranges. In this technique, the scattered fields of a flat plate in the diagonal plane are measured in a range for various frequencies and look angles. The scattered field data are then processed to generate an inverse synthetic aperture radar (ISAR) image of the diagonal flat plate. It is shown that scattering mechanisms associated with various stray signals can be identified by using the ISAR image. This leads to better understanding of the range and possible chamber improvements. Scattering mechanisms as small as 90 dB below the plate broadside scattered field level have been observed in the image domain due to the high directivity and low sidelobe characteristics associated with the diagonal flat plate backscattered fields. The results obtained from evaluating the two compact range facilities at the Ohio State University ElectroScience Laboratory are presented to illustrate the virtues of the range evaluation technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Enhanced imaging of reflector antenna surface distortion using microwave holography

Two signal processing techniques are discussed that improve the accuracy of a microwave holographic measurement by removing unwanted signals from the aperture distribution: pattern simulation and subtraction, and time domain filtering. Pattern simulation and subtraction involves modeling unwanted scattering mechanisms and then removing them from the measured far‐field data. Time domain gating requires a swept frequency measurement of each far‐field point to separate undesired scattering mechanisms from the desired response. Measurements taken on a focal point geometry and a Cassegrain geometry at 11 GHz in the Ohio State University ElectroScience Laboratory Compact Range provided excellent amplitude and phase stable data to be processed by the holographic analysis system. Pattern simulation and subtraction was applied to both geometries. Surface deformation profiles generated for the Cassegrain antenna by this system were compared to an optical measurement of the main reflector surface. Good agreement was obtained. Because of system limitations, time domain filtering could not be applied.

The Ohio state university electroscience laboratory

The Ohio state university electroscience laboratory

Summary of GTD Computer Codes Developed at the Ohio State University

This paper briefly describes three user-oriented computer codes developed at the Ohio State University ElectroScience Laboratory: namely, the On-Aircraft Antenna Code, the Basic Scattering Code, and the Reflector Antenna Code. Each code uses the Geometrical Theory of Diffraction (GTD). An example is used to describe the basic GTD approach for all three codes. A brief description is given for each code which includes sample results compared to measurements.