Ultrawideband Random Noise Radar Research Articles

Through-Wall Imaging of Moving Targets Using UWB Random Noise Radar

For a through-wall ultrawideband (UWB) random noise radar using array antennas, subtraction of successive frames of the cross-correlation signals between each received element signal and the transmitted signal is able to isolate moving targets in heavy clutter. Images of moving targets are subsequently obtained using the back projection (BP) algorithm. This technique is not constrained to noise radar, but can also be applied to other kinds of radar systems. Different models based on the finite-difference time-domain (FDTD) algorithm are set up to simulate different through-wall scenarios of moving targets. Simulation results show that the heavy clutter is suppressed, and the signal-to-clutter ratio (SCR) is greatly enhanced using this approach. Multiple moving targets can be detected, localized, and tracked for any random movement.

Doppler visibility of coherent ultrawideband random noise radar systems

Random noise radar has recently been used in a variety of imaging and surveillance applications. These systems can be made phase coherent using the technique of heterodyne correlation. Phase coherence has been exploited to measure Doppler and thereby the velocity of moving targets. The Doppler visibility, i.e., the ability to extract Doppler information over the inherent clutter spectra, is constrained by system parameters, especially the phase noise generated by microwave components. Our paper proposes a new phase noise model for the heterodyne mixer as applicable for ultrawideband (UWB) random noise radar and for the local oscillator in the time domain. The Doppler spectra are simulated by including phase noise contamination effects and compared with our previous experimental results. A genetic algorithm (GA) optimization routine is applied to synthesize the effects of a variety of parameter combinations to derive a suitable empirical formula for estimating the Doppler visibility in dB. According to the phase noise analysis and the simulation results, the Doppler visibility of UWB random noise radar depends primarily on the following parameters: 1) the local oscillator (LO) drive level of the receiver heterodyne mixer, 2) the saturation current in the receiver heterodyne mixer, 3) the bandwidth of the transmit noise source, and 4) the target velocity. Other parameters such as the carrier frequency of the receiver LO and the loaded quality factor of the LO have a small effect over the range of applicability of the model and are therefore neglected in the model formulation. The Doppler visibility curves generated from this formula match the simulation results very well over the applicable parameter range within 1 dB. Our model may therefore be used to quickly estimate the Doppler visibility of random UWB noise radars for trade-off analysis

Inverse synthetic aperture radar imaging using a coherent ultrawideband random noise radar system

The University of Nebraska-Lincoln has developed an ultrawideband random noise radar operating over the 1- to 2-GHz frequency range. The system uses the technique of heterodyne correlation, and is thus phase coherent. It has therefore been used in applications such as interferometry, polarimetry, and Doppler estimation. This assesses the performance of this radar as a range-Doppler imaging system, in particular, inverse synthetic aperture radar (ISAR). By performing turntable experiments, we examine a number of issues that arise both from the wideband nature of the radar system and from the randomness of the transmit signal. Although the ultrawideband nature of the signal does yield some ambiguity as to the cross-range resolution of the system, it is seen that one may use the usual equation for cross-range resolution in narrowband systems with reasonable confidence. In addition, the random nature of the transmit waveform gives rise to variations from look to look in the ISAR images. High correlations are obtained for voltage and power amplitudes, while the complex voltage and the phase angle show low correlations from look to look. Finally, we present polarimetric color images of a complex target that captures its polarimetric scattering characteristics, which may be useful in automatic target recognition.

Receiver operating characteristics for the coherent UWB random noise radar

An ultrawideband (UWB) random-noise radar operating in the 1-2 GHz frequency band has been developed and held-tested at a 200 m range at the University of Nebraska. A unique heterodyne correlation technique based on a delayed transmitted waveform using a photonic delay line has been used to inject coherence within this system. The performance of this radar, assuming a point target, has been investigated from a statistical point of view by developing the theoretical basis for the system's receiver operating characteristics (ROC). Explicit analytical expressions for the joint probability density function (pdf) of the in-phase (I) and quadrature (Q) components of the receiver output have been derived under the assumption that the input signals are partially correlated Gaussian processes. The pdf and the complementary cumulative distribution function (cdf) for the envelope of the receiver output are also derived. These expressions are used to relate the probability of detection (P/sub d/) to the probability of false alarm (P/sub f/) for different numbers of integrated samples, and the results are analyzed.

Range sidelobe suppression technique for coherent ultra wide-band random noise radar imaging

When applied in airborne imaging surveillance, ultra wide-band (UWB) random noise radars have their special merits. Because of the randomness and the ultrawide bandwidth of the transmit and receive signals, such radars can be used for covert detection and identification, and are immune from hostile detection and jamming while preserving very high range resolution. However, the images are plagued with artifacts caused by high range sidelobes. In this paper, a new technique for the range sidelobe suppression of UWB random noise radar, which combines median and apodization filtering, is proposed. Computational and experimental results show the effectiveness of this image enhancement procedure.

Design, performance, and applications of a coherent ultra-wideband random noise radar

Ram M. NarayananYi XuPaul D. HoffmeyerUniversity of Nebraska—LincolnCenter for Electro-OpticsDepartment of Electrical EngineeringLincoln, Nebraska 68588-0511E-mail: rnarayanan@unl.eduJohn O. CurtisU.S. Army Waterways Experiment StationEnvironmental LaboratoryVicksburg, Mississippi 39180-6199Abstract. A novel coherent ultra-wideband radar system operating inthe 1- to 2-GHz frequency range has been developed recently at theUniversity of Nebraska. The radar system transmits white Gaussiannoise. Detection and localization of buried objects is accomplished bycorrelating the reflected waveform with a time-delayed replica of thetransmitted waveform. Broadband dual-polarized log-periodic antennasare used for transmission and reception. A unique signal-processingscheme is used to inject coherence into the system by frequency trans-lation of the ultrawideband signal by a coherent 160-MHz phase-lockedsource prior to performing heterodyne correlation. The system coher-ence allows the extraction of a target’s polarimetric amplitude and phasecharacteristics. This paper describes the unique design features of theradar system, develops the theoretical foundations of noise polarimetry,provides experimental evidence of the polarimetric and resolution capa-bilities of the system, and demonstrates results obtained in subsurfaceprobing applications.