F. Le Chevalier

Space-time radar waveforms: circulating codes

This paper describes a concept of the circulating codes covering the whole class of the space-time codes. The circulating codes do not narrow the radiated pattern of the antenna array, thus providing a wide angular coverage, possibly tunable. In turn, the beam-forming on transmit is achievable by means of the signal processing in one (or each) receiver channel. The modelling results demonstrate the efficiency of the circulating codes based on their multidimensional ambiguity functions.

Optimization of low sidelobes radar waveforms: Circulating codes

This paper presents two techniques as well as their combination for optimization of the low side-lobes space-time waveforms: circulating LFM signals. Matched filtering is implemented for the pulse compression. The ambiguity functions of the modified waveforms are analyzed for demonstration of the optimization efficiency. The simulation results show that the proposed techniques decrease the range side-lobes, with no penalty on the signal-to-noise ratio, and restore the range resolution in the beam-formed angular direction where the circulating LFM signal previously had a resonance effect. Typical sidelobe levels lower than -50dB are demonstrated over the whole angular coverage, with an 8 element antenna and 256 length codes.

Future ocean scatterometry at very strong winds

The growing interest in achieving a better understanding of the physics that governs the cross-polar scattering of microwave radiation from ocean is triggered by recent measurement campaigns over hurricanes performed by NOAA Hurricane-Hunter winds and RADARSAT-2 [1]. From this data set the cross-polarized signals showed no evident loss of sensitivity as the wind-speed increased from 20 m/s up to 45 m/s. On the contrary C-band co-polar backscatter suffered from problems of incidence and azimuth angle-dependent signal saturations and dampening which makes it weakly sensitive above 25 m/s. On the basis of these considerations there are good reasons to think that the cross-polarized data can be a valuable tool for the retrieval of strong-to-severe wind speeds for future scatterometers. In this paper we present a physical scattering model based on the Small Slope Approximation theory [2] in conjunction with the Vector Radiative Transfer Theory [3] to describe the behavior of cross-polar scattering from ocean as function of the wind-speed and direction. Numerical results will be compared with real data from RADARSAT-2 and the brand new empirical Geophysical Model Function GMF-VH [1].

An investigation on sea surface wave spectra and approximate scattering theories

In this paper, we present a survey of some of the most common analytical approximate models that are used to describe the microwave sea surface scattering. The main strengths and weaknesses of the various methods are identified and critically discussed. Such models combine an adequate sea surface description with advanced electromagnetic theories to simulate both monostatic and bistatic scattering for a wide range of wind speeds, radar frequencies, incidence angles, different polarizations and arbitrary radar look direction with respect to the wind direction. Theoretical calculations for co-polar signals in C-band and Ku-band are in good overall agreement with the experimental data represented by the empirical models, CMOD5 and NSCAT, with the exception of HH-polarization at high incidence angles (above 40°). A parametric analysis on the sea surface spectrum, will demonstrate that the discrepancy between the measured and the simulated HH normalized radar cross-sections, is only in part due to the inefficiency of the spectrum and mostly due to additional scattering contribution from breaking waves, not taken into account by the most common analytical scattering theories.

Clutter calibration for space-time airborne MTI radars

For slow target detection with airborne array radar, the ground clutter Doppler spreading due to the platform movement is a limiting factor, especially for long wavelength radar. It is shown that two procedures for slow target detection (Doppler-angle imaging or space-time processing, and movement compensation) are equivalent, and that an original real-time procedure for antenna array calibration using clutter returns can be combined with these detection techniques to increase subclutter visibility in the presence of high clutter returns.

DOPSCAT: A mission concept for a Doppler wind-scatterometer

The present paper proposes an innovative mission concept for a C-band fan-beam wind scatterometer with both ocean wind vector and ocean current vector measurement capability on a global scale.

Self-similarity matrix based slow-time feature extraction for human target in high-resolution radar

A new approach is proposed to extract the slow-time feature of human motion in high-resolution radars. The approach is based on the self-similarity matrix (SSM) of the radar signals. The Mutual Information is used as a measure of similarity. The SSMs of different radar signals (high-resolution range profile, micro-Doppler, and range-Doppler video sequence) are compared, and the angel-invariant property of the SSMs is demonstrated. The SSM for different activities (i.e. walking and running) is extracted from range-Doppler video sequence and analyzed. Finally, simulation result is validated by experimental data.

An unambiguous radar mode with a single PRF wideband waveform

In this paper, we consider the problem of unambiguously estimating targets, including in blind velocities, using a single-low-PRF wideband radar signal. We present a Bayesian sparse recovery algorithm able to estimate the amplitude and location of range-migrating targets possibly straddling range-velocity bins embedded in colored noise. Numerical simulations on synthetic data and experimental data show that the proposed algorithm is able to mitigate velocity ambiguity and estimate targets in blind velocities.

Improved calibration technique for the transmit beamforming by a coherent MIMO radar with collocated antennas

In this paper we present a calibration method for mitigating the effects of mutual coupling affecting the signal radiated by MIMO radar with collocated antennas. The paper contains the measurement results that verify the proposed method. The improved scan-dependent calibration technique is proposed for elimination of the coupling effect. The experiments with a real X-band antenna array validate the calibration procedure presented in this paper.