F. Perez-Martinez

RF Front-End Concept and Implementation for Direct Sampling of Multiband Signals

The placement of the analog-to-digital converter as near the antenna as possible is a key issue in the software-defined radio receiver design. Direct sampling of the incoming filtered signal is a compact solution enabling channel simultaneity. In this brief, in the context of evenly spaced equal-bandwidth multiband systems, sufficient conditions for the channel allocation assuring that the minimum sub-Nyquist sampling frequency does not imply aliasing are provided. Subsequently, as a validation example, the design of a minimum-sampling-frequency acquisition system for quad-band applications within a ultrawideband frequency range is shown. Moreover, an innovative solution for its radio-frequency front end, basically consisting of a signal-interference multiband bandpass filter, is reported. Experimental results of the built microstrip-filter prototype for the proposed 1-3-GHz-range quad-band system are also given.

Traffic Surveillance System Based on a High-Resolution Radar

Traffic surveillance is an important civilian application of radars. The current high-resolution radars give new opportunities so that the traffic application may be redefined. In this paper, a traffic scenario with a high-resolution radar is presented. A range-bin alignment method, the Global Range Alignment, which comes from the focusing techniques in inverse synthetic aperture radar, is applied to obtain further capabilities than the usual velocity measurement: distinction between vehicle types via length estimation and adequate management in situations with simultaneous targets. Preliminary results from a real scenario using a high-resolution linear frequency-modulated continuous-wave millimeter-wave radar are shown.

Motion compensation for ISAR based on the shift-and-convolution algorithm

ISAR (inverse synthetic aperture radar) is a coherent technique that obtains images of targets by processing the echoes returned during the dwell time. A higher angular resolution than the antenna beamwidth may be obtained. In this paper we report high resolution ISAR images, which have been obtained from data captured by a millimeter-wave LFMCW (linear frequency modulated continuous wave) radar. The target translational motion compensation is achieved by means of a new parametric algorithm, which makes use of the shift-and-convolution technique. This image autofocusing algorithm is compared with prominent point processing (PPP) and phase gradient autofocus (PGA). Simulated and real data from the millimeter-wave LFMCW radar are used to verify the proposed technique, although the method is also applicable to any kind of coherent radar.

A shift-and-convolution technique for high-resolution radar images

Theoretical and experimental results of a new method able to obtain images with high-resolution radars (HRRs) are presented in this paper. This algorithm does not need the data-phase information of the signal reflected by targets; it only uses the extracted noncoherent data. The proposed procedure works on real time, and it is compatible with the scanning and tracking radar functions. The technique consists of a modification and adaptation of algorithms used for the synchronization of the actual digital communication systems. Experimental results have been obtained with ARIES radar, a surface marine and coast surveillance HHR developed by INDRA SISTEMAS S.A. in collaboration with the Technical University of Madrid. The Spanish Ministry of Defence founded this research.

SIMPLE TRAFFIC SURVEILLANCE SYSTEM BASED ON RANGE-DOPPLER RADAR IMAGES

A simple tra-c surveillance system based on the extraction of features from range-Doppler radar images is addressed. The concept exploits the High-Resolution Radars (HRR) properties. Speciflcally, a procedure is proposed to obtain some features from the HRR non-cooperative targets to enable their classiflcation. These features are the distance, radial velocity, radial longitudinal dimension of the target, its integrated range-Doppler image based on a group of range-Doppler frames from each target, and both the coherent and non-coherent integrated range proflles. Experimental results from real scenarios using a high-resolution Linear-Frequency-Modulated Continuous-Wave (LFMCW) millimetre-wave radar are shown.

Subinteger range-bin alignment method for ISAR imaging of noncooperative targets

Inverse Synthetic Aperture Radar (ISAR) is a coherent radar technique capable of generating images of noncooperative targets. ISAR may have better performance in adverse meteorological conditions than traditional imaging sensors. Unfortunately, ISAR images are usually blurred because of the relative motion between radar and target. To improve the quality of ISAR products, motion compensation is necessary. In this context, range-bin alignment is the first step for translational motion compensation. In this paper, we propose a subinteger range-bin alignment method based on envelope correlation and reference profiles. The technique, which makes use of a carefully designed optimization stage, is robust against noise, clutter, target scintillation, and error accumulation. It provides us with very fine translational motion compensation. Comparisons with state-of-the-art range-bin alignment methods are included and advantages of the proposal are highlighted. Simulated and live data from a high-resolution linear-frequency-modulated continuous-wave radar are included to perform the pertinent comparisons.

Radar Signature of a Helicopter Illuminated by a Long LFM Signal

Helicopters exhibit a very particular Doppler radar signature caused by the movement of rotor blades. This signature can easily be derived using a short-time approximation: the blades are assumed to be static during each pulse. In wideband linear frequency modulated (LFM) radars, however, this assumption cannot be made. The work presented here describes the echo of rotary blades illuminated by LFM radars without the short-time assumption and provides useful information for detection and recognition purposes.

Focused ISAR images of maritime targets using a high resolution LFMCW millimeter-wave radar

The generation of high resolution ISAR (inverse synthetic aperture radar) images is reaching protagonism at the present time. A major application is coast surveillance. The recognition and the identification of maritime targets are important tasks. In this paper experimental results of ISAR images of maritime targets are reported. The data were captured with an LFMCW (linear frequency modulated continuous wave) millimeter-wave radar. High resolution ISAR images are obtained, since a great bandwidth (1 GHz) is transmitted. In ISAR the target motion can degrade the quality of the final images and motion compensation algorithms are necessary to improve the focus of these images. An autofocusing technique based on the shift-and-convolution algorithm is used to compensate the translational target motion and a two-phase algorithm (slant range rotation compensation (SRRC) and cross range rotation compensation (CRRC)) is used to correct the migration through resolution cells (MTRC) associated with the target rotation. The effectiveness of the focusing techniques is verified with simulated and real (maritime targets) radar data and compared with the standard range-Doppler algorithm (RDA)

Multi-Band Radar Receiver Design Approach for Minimum Bandpass Sampling

Multi-frequency radars, which are employed in a plurality of emerging applications, exploit the echoes for different bands that come from illuminated targets. A compact multi-function architecture that makes use of direct sampling could be a preferable choice for these new-generation radar systems, with RF front-end design a first step in their development. Here, within the framework of multi-frequency radars, an analytical tool for simultaneously acquiring the signal bands by using the minimum sub-Nyquist sampling frequency is addressed. Although the dual-band radar scenario is exhaustively analyzed, keys to understand the acquisition of more-than-two-band systems are also provided. Moreover, as the core of the associated RF architecture to carry out arbitrary multi-band signal pre-selections, a new class of microwave planar multi-passband filters based on stepped-impedance-line signal-interference concepts is reported. Also, for validation, the construction and testing of a microstrip spectrally-asymmetrical dual-passband filter prototype for a specific example of minimum-sampling dual-frequency radar RF front-end are shown.

Monitoring road traffic with a high resolution LFMCW radar

The current development of the high resolution concept allows to redefine standard applications of radars, like the measurement of the motion parameters of road traffic. High resolution radars may be used to monitor the road traffic. In this paper, live captures from a high resolution linear frequency modulated continuous wave (LFMCW) millimeter-wave radar are shown. For the estimation of the dynamics of the simultaneously illuminated targets, two approaches are described. The first one is a tracking-based technique of the vehicle echoes in the range-Doppler-slow time domain. The second one uses a range bin alignment technique, extracted from the inverse synthetic aperture radar (ISAR) world. This second approach works in the range profile domain. Both algorithms give similar results in the estimation of the speed of the vehicles. However, there are some divergences in the estimates of the accelerations. We hope that both algorithms may be useful for the future traffic surveillance systems.