KEYWORDS: Radar, X band, Solid modeling, Scattering, Computer aided design, 3D modeling, Design and modelling, Data modeling, V band, Time-frequency analysis
Micro-Doppler radar signatures of helicopters and drones are gaining increasing importance. However, collecting data under controlled conditions on drones in flight can be difficult. The ability to use predictive codes to produce moving target and micro-Doppler radar data is becoming more important. In order to demonstrate the potential use of computer code predictions, this report will describe the X, V, and W-Band micro-Doppler signatures for the DJI Phantom 2 quadcopter. The predictions are generated using the Xpatch prediction code. The motion of all four propellers are simulated for realistic flight conditions. Predictions were performed at multiple viewing angles and using various PRF values. Additionally, different range resolutions were also predicted. The data is analyzed using a series of Range-Doppler spectrograms and short time Fourier transforms. The equations for the motion of the blades are examined in the context of the minimum PRF that is needed for capturing the micro-Doppler information. A discussion is included for finding the best frequency band to operate which balances the tradeoff of information content with operating frequency and PRF value. It is shown in the standard analysis that the unique shape of the blades produced patterns in the micro-Doppler signature that may be of use in target identification. Application of Time-Frequency-Analysis is also demonstrated. The predicted data is compared with micro-Doppler data measured in the laboratory using a 100 GHz compact range on a real Phantom 2 drone.
Utilizing a generalized spotlight SAR data collection formalism described in the literature, we demonstrate a technique whereby the generalized planar flight path as well as more arbitrary collection surfaces may be analyzed in the physical scale model compact radar range environment. We briefly review the generalized planar collection geometry, its characteristics, and the implications of collecting spotlight SAR data across non-planar surfaces. Using data collected in a 305-375 GHz compact radar range, we present first results of spotlight SAR imagery modeling the generalized planar collection geometry as well as a more arbitrary geometry at X-band using 1/35th physical scale model objects. The scene observed in this work consisted of a test scene consisting of canonical scatterers as well as a scene composed of a 1/35th scale model SA-6 that exemplifies the limits of depth of focus due to non-planar motion. Our imagery results are produced from both squint and broadside collections.
Generation of moving target (Doppler and micro-Doppler) radar data on a scale-model helicopter with an arbitrary flight path is described. Fully-polarimetric micro-Doppler radar signatures of a 1/35th scale helicopter at S-Band were measured using a 100GHz compact range and are examined under several different situations. The motion of the rotor and blades are analyzed using standard range-doppler spectrograms. In particular, the effect of radial motion toward or away from the radar is considered and the consequences this motion will have on the range/doppler spectrogram of the radar data. It is found that a helicopter exhibiting no radial velocity will experience a degeneracy of signals from the rotation of the helicopter blades. This degeneracy is lifted when a non-zero radial motion is experienced. The effect of varying the radar pulse repetition frequency will be examined.
KEYWORDS: Data modeling, Radar, 3D acquisition, 3D modeling, Compressed sensing, Scattering, Solid modeling, 3D metrology, Computer aided design, 3D image processing
Three-dimensional radar imaging is becoming increasingly important in modern warfare systems, leading to an increased need for deeper understanding of the 3D scattering behavior. Fully polarimetric, three-dimensional radar signature data have been collected using 1/16th scale models of tactical targets in several indoor compact radar ranges, corresponding to radar data at X-band. The high-range-resolution data has been collected through a 2D aperture in azimuth and elevation. This data has been processed into 3D coordinates using a standard 3D Fourier transform. The radar signatures have also been rendered into 3D coordinates using Interferometric ISAR techniques. The results of applying compressed sensing techniques to the analysis will be presented. Mathematical 3D correlation analysis has been used to compare the results of each method of 3D reconstruction.
Compressed sensing is a signal processing paradigm enabling the acquisition and successful reconstruction of a sparse signal from a reduced set of measurements, potentially in violation of the Nyquist sampling criterion. In this paper the results of preliminary investigations into Compressed Sensing applied to the acquisition of wide bandwidth millimeterwave compact radar range data are presented. Primary motivations for application of Compressed Sensing to compact radar range acquisition and imaging include increasing data acquisition speed as well as reducing required data storage. In this work only signal reduction in the frequency domain is examined. Compressed Sensing fully-polarimetric compact range data acquisition and imaging for both a simple canonical target (cylinder) and a complex target (Slicy) are presented as radar cross section (RCS) measurements and interferometric inverse synthetic aperture radar (IFISAR) images. Correlations of compact range data provide a measure of error between the reconstructed and complete data sets as a function of target complexity and sub-sampling rate.
We present a prototype bistatic compact radar range operating at 160 GHz and capable of collecting fullypolarimetric radar cross-section and electromagnetic scattering measurements in a true far-field facility. The bistatic ISAR system incorporates two 90-inch focal length, 27-inch-diameter diamond-turned mirrors fed by 160 GHz transmit and receive horns to establish the compact range. The prototype radar range with its modest sized quiet zone serves as a precursor to a fully developed compact radar range incorporating a larger quiet zone capable of collecting X-band bistatic RCS data and 3D imagery using 1/16th scale objects. The millimeter-wave transmitter provides 20 GHz of swept bandwidth in the single linear (Horizontal/Vertical) polarization while the millimeter-wave receiver, that is sensitive to linear Horizontal and Vertical polarization, possesses a 7 dB noise figure. We present the design of the compact radar range and report on test results collected to validate the system’s performance.
KEYWORDS: Polarimetry, Scattering, Polarization, Ka band, 3D modeling, Data modeling, Automatic target recognition, Radar, Target recognition, 3D acquisition
In this study the polarization scattering matrices (PSM) of individual scatterers from a complex tactical ground target were measured as a function of look angle. Due to the potential value of PSMs in studies of automatic target recognition, a fully polarimetric, 3D spot scanning radar modeling system was developed at 1.56 THz to study the W- band scattering feature behavior from 1/16th scale models of targets. Scattering centers are isolated and coherently measured to determine the PSMs. Scatterers of varying complexity from a tactical target were measured and analyzed, including well-defined fundamental odd and even bounce scatterers that maintain the exact normalized PSM with varied look angle, scatterers with varying cross- and co-pol terms, and combination scatterers. Maps defining the behavior of the position and PSM activity over varying look angle are likely to be unique to each target and could possibly represent exploitable features for ATR.
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