The US Army Research Laboratory (ARL) has recently developed the Spectrally Agile Frequency-Incrementing Reconfigurable (SAFIRE) radar system during its ongoing research to provide ground vehicular standoff detection and classification of obscured and/or buried explosive hazards. The system is a stepped-frequency radar (SFR) that can be reconfigured to omit operation within specific sub-bands of its 1700 MHz operating band (300 MHz to 2000 MHz). It employs two transmit antennas and an array of 16 receive antennas; the antenna types are quad-ridged horn and Vivaldi, respectively. The system is vehicle-mounted and can be interchanged between forward- or side-looking configurations. In order to assess and evaluate the performance of the SAFIRE radar system in a realistic deployment scenario, ARL has collected SAFIRE data using militarily-relevant threats at an arid US Army test site. This paper presents an examination of radar imagery from these data collection campaigns. A discussion on the image formation techniques is presented and recently processed radar imagery is provided. A summary of the radars performance is presented and recommendations for further improvements are discussed.
An S-Band, half-wave length, probed-fed, two-patch (uniformly linear array 2 x 1 configuration) array antenna is
presented. The array was constructed using an air dielectric between the patch and ground plane. The two-metal patches
have coaxial feeds with type N (or HN) connectors and are supported by two metal posts positioned for bandwidth
enhancement. In addition, these patches are separated at prescribed distance and locations for obtaining electrical
performance in terms of antenna pattern and gain. The array can produce a maximum achievable gain of 11.5 dBi with
broad azimuthal angle. The antenna's architecture is low profile and suitable for platform integration such as airborne as
well as ground radar systems. The design is unique, reproducible, and affordable for manufacturing a low cost radar
system. The paper will present the design of the antenna, experimental data, and its implementation.
For most radar or ladar systems range information is obtained from the time necessary for an electromagnetic pulse to propagate to a target and return to a receiving antenna. In contrast, we investigate a method that replaces temporal encoding of distance with spatial encoding. In particular, we use a self-referencing superposition of Laguerre-Gaussian beams to translate propagation distance into transverse rotation of cross-section of the beam intensity. We review the mathematical foundations of the technique and discuss models for simulating its performance in turbulent atmosphere. In addition, we present a simple technique to extract the rotation angle from a two-dimensional cross-section of the beam. Preliminary results indicate that the technique is robust with respect to propagation in a turbulent atmosphere.
Laguerre-Gaussian beams are considered as basis functions for inverse scattering applications. First order perturbation theory is applied to paraxial higher order Gaussian beams. Information about the scattering potential is deduced from the coupling coefficients between otherwise orthogonal modes. This leads to a theoretical description analogous to plane wave diffraction tomography. Differences between the plane wave model and the Laguerre-Gauss formalism highlight both limitations as well as opportunities for applying singular Gaussian beams to the inverse scattering problems. The perturbation analysis is applied to a number of examples illustrating how information about the scattering object can be deduced from measurements of the scattered paraxial field.
Scan-MUSIC algorithm, developed by the U.S. Army Research Laboratory (ARL), improves angular resolution for target detection with the use of a single rotatable radar scanning the angular region of interest. This algorithm has been adapted and extended from the MUSIC algorithm that has been used for a linear sensor array. Previously, it was shown that the SMUSIC algorithm and a Millimeter Wave radar can be used to resolve two closely spaced point targets that exhibited constructive interference, but not for the targets that exhibited destructive interference. Therefore, there were some limitations of the algorithm for the point targets. In this paper, the SMUSIC algorithm is applied to a problem of resolving real complex scatterer-type targets, which is more useful and of greater practical interest, particular for the future Army radar system. The paper presents results of the angular resolution of the targets, an M60 tank and an M113 Armored Personnel Carrier (APC), that are within the mainlobe of a Κα-band radar antenna. In particular, we applied the algorithm to resolve centroids of the targets that were placed within the beamwidth of the antenna. The collected coherent data using the stepped-frequency radar were compute magnitudely for the SMUSIC calculation. Even though there were significantly different signal returns for different orientations and offsets of the two targets, we resolved those two target centroids when they were as close as about 1/3 of the antenna beamwidth.
KEYWORDS: Antennas, Radar, Detection and tracking algorithms, Signal to noise ratio, Computer simulations, Monte Carlo methods, Algorithm development, Extremely high frequency, Constructive interference, Super resolution
Step-scanned radar antennas represent a new application of radar technology for detection of targets and estimation of their locations. In this paper we describe a new development called Scan-MUSIC (SMUSIC), which extends the application of the MUSIC algorithm to improve the cross-range resolution of closely spaced point targets with a step-scanned radar. This paper also demonstrates that SMUSIC can be used with radar data obtained with an experimental Millimeter Wave (MMW) coherent scanning radar. While a mathematical proof of resolvability has not yet been established for the scanning antenna, we have shown that we can apply the spatial smoothing method to the SMUSIC algorithm to estimate the closely spaced point targets that are within the beamwidth of the radar antenna. The results show that the targets that are spaced less than 1/4 of the antenna beamwidth and are interfering can be resolved with SMUSIC in constructive interference case. This paper also presents the performance of the SMUSIC superresolution algorithm for the scanning antenna in terms of probability of successful resolution and the total average mean-squared error of target locations, based on the simulated data generated by using an experimental antenna pattern.
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