A. Asensio-Lopez

Universidad Politécnica de Madrid, Madrid, Madrid, Spain

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Publications (29)15.4 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper a performance analysis on recorded live data of some detectors for range-spread targets is developed. To this end, real target and sea-clutter data collected by a fully coherent Ka-band radar system, featuring submeter range resolution, are used. The study is of particular interest for homeland security radar applications where a careful coastal control is necessary to prevent the arrival of nonauthorized small boats. The performance of both rank-one and subspace range-spread target detection strategies is analyzed, both in terms of constant false alarm rate (CFAR) behavior and in terms of detection capabilities. With reference to the former issue, clutter-only datafiles are used whereas, concerning the latter data containing both real target and clutter are used. The targets returns come from typical small boats (such as inflatable, wooden, and patrol boats) appearing range distributed at the resolution of the exploited radar system. Range-time detection maps are shown, assessing the capability of the analyzed processors to detect the aforementioned targets of great interest for homeland coastal security. Finally, the performance improvements achievable by over-resolving the target is quantified.
    IEEE Transactions on Aerospace and Electronic Systems 01/2012; 48(3):2216-2238. · 1.30 Impact Factor
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    ABSTRACT: This paper presents the results of an extensive experimental parametric analysis of coherent radar detectors exploiting a new Ka-band high-resolution sea-clutter database. The statistical analysis of the submeter range resolution real data shows strong fluctuations of both the spectral shape and power between adjacent range cells. This highly heterogeneous dataset is therefore ideally suited to characterize the performance degradation to be expected in real conditions, relative to the homogeneous finite-sample-support case. The impact of spectral heterogeneity within the reference window of the detectors is quantified by resorting to simulated datafiles. The analysis focuses on both the experimental constant false alarm rate (CFAR) behavior and the synthetic Swerling I target probability of detection. Finally, a comparison with a practical detection scheme is included, allowing the trade-off between increased computational complexity and improvement in performance over conventional approaches to be assessed.
    IEEE Transactions on Aerospace and Electronic Systems 08/2011; · 1.30 Impact Factor
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    ABSTRACT: This paper shows a High-Range Resolution (HRR) Radar prototype development, transmitting in millimeter-wave band. The waveform selected to be used is the continuous-wave linear frequency modulation (CWLFM), which allows, at the same time, good range resolution, moderate unambiguous doppler range and reasonable operational range taking into account that high-frequency band is used. The radar prototype looks for High-Range Resolution (HRR) characteristics as well as flexibility, in order to obtain the best Inverse Synthetic Aperture Radar (ISAR) images possible depending on the applications and targets involved. That is, depending on the speed and target's trajectories, some radar features, such as transmitted bandwidth, modulator frequency or sampling frequency, play a key role in obtaining the best possible results while using lowest electrical requirements.
    IEEE Sensors Journal 03/2011; · 1.48 Impact Factor
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    ABSTRACT: This paper presents the design of microstrip to stripline transitions built on the same layer of substrate of a single LTCC wafer. To achieve this geometry a cavity is opened on the substrate layer just above the stripline removing the upper ground plane, morphing the stripline into a microstrip line. The main interest of these transitions is the ability to excite stripline circuits directly from the same layer, as well as use them as 50Ω matched interconnection between buried lines and MMIC's. Two transitions of this kind are realized and measured. Comparison of measured circuits and simulations provide insight on what are the effects of the fabrication tolerance of critical structures, such as substrate cavities and ground planes.
    Microwave Workshop Series on Millimeter Wave Integration Technologies (IMWS), 2011 IEEE MTT-S International; 01/2011
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    ABSTRACT: High resolution Ka-band radar data corresponding to small maritime targets and target-free sea-clutter acquisitions are used to evaluate the experimental performance of range dis- tributed target coherent detectors. The statistical analysis of the sub-meter range resolution clutter data shows strong fluctuations of both the spectral shape and power between adjacent range cells. The assessment of the impact of this highly heterogeneous disturbance in the CFAR behavior of distributed target detectors is a key aim of this work. Additionally, the availability of coherent target data at a range resolution of 0.08m, 0.16m and 0.8m has been exploited to analyze the detection performance of both subspace and rank one detection approaches. I. INTRODUCTION In maritime surveillance applications a significant perfor- mance improvement can be achieved by deploying high res- olution radars (1). Recent technological breakthrough in key areas such as real-time digital signal processing hardware, or very high bandwidth RF front-ends, are now turning radar systems foreseen two decades ago into a practical reality (2). This fact is particularly important for homeland security tasks such as border control or coastal surveillance. Several works have shown that properly designed detectors for targets distributed across several range cells, or distributed targets, outperform lower resolution systems in which the target is confined within a single range cell (3). Two main reasons are behind this fact. Firstly, reducing the size of the resolution cell is a straightforward technique to diminish dis- turbance returns in the very frequent distributed-clutter-limited detection scenario. Secondly, radar backscatter from range- resolved target scatterers exhibits a less fluctuating behavior that improves the detection performance. High resolution systems benefit from the reduced fluctuation losses. However, increasing the range resolution of the maritime surveillance radar system has at least two drawbacks that must be accounted for in the radar design process so as to benefit from the aforementioned potential performance improvement: the need to process over-resolved targets with their energy distributed across several adjacent range bins and the non- Gaussian and non-stationary statistics associated with high resolution sea-clutter. In this context, experimental high resolution coherent data of both small maritime targets and sea-clutter is required to evaluate the actual performance of a particular detection strategy under real-life conditions. This paper presents results from an extensive experimental analysis of range distributed target detectors, and is part of a series of works exploiting the availability of a sub-meter range resolution data set obtained with an in-house developed continuous wave linear frequency modulated Ka-band system. In particular, the statistical anal- ysis of the sea-clutter database was described in detail in (4), the experimental performance of point-target detectors was the topic of (5) and a Radon transform based non-coherent detection approach was evaluated in (6). To the author's knowledge this is the first analysis on real data of range distributed target detectors available in open literature for sub- meter very high range resolutions.
    IEEE National Radar Conference - Proceedings 01/2011;
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    ABSTRACT: This paper presents a collection of five filters in Ka-band using low temperature co-fired ceramic (LTCC) technology. Its purpose is to show an overview of the compacting possibilities with final sizes of complex designs in LTCC. The coupling matrix method is used in order to synthesize the frequency response of the filters, and the designs are carried out doing a systematic characterization of every coupling structure. A coupling matrix optimization CAD is used to extract coupling coefficients and resonant frequencies, making the tuning of the resonators easier. Two filters are designed with single and dual-mode patch resonators. The rest of the designs are cavity filters; one of these combines different coupling structures, using two different layers where the cavities are situated in order to reduce the final size. Finally, an overall comparison of sizes and insertion losses is given.
    Microwave Workshop Series on Millimeter Wave Integration Technologies (IMWS), 2011 IEEE MTT-S International; 01/2011
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    ABSTRACT: This paper presents the statistical analysis of an experimental high-resolution sea-clutter database, collected with a high-resolution Ka-band radar at the south coast of Spain. The main motivation of this paper has been to check the validity of the available theoretical models for high-resolution sea-clutter against data corresponding to a range resolution of centimeters. The overall amplitude probability density function (pdf), the compatibility with a compound representation, and the average spectral behavior of the data are analyzed in detail. Results clearly show the suitability of the compound Gaussian model and, more precisely, that the empirical pdf is well modeled by the generalized K distribution with log-normal texture. A close agreement has also been found between the estimated clutter spectral density and a power-law model.
    IEEE Transactions on Geoscience and Remote Sensing 05/2010; · 3.47 Impact Factor
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    ABSTRACT: Scan rate selection has a crucial impact on the performance of maritime surveillance systems. In this work, a sea clutter database has been used to obtain experimental insight on the trade-off between within-scan and scan-to-scan integration. This paper extends the previous empirical studies to the case of sub-meter range resolution Ka-band coherent sea-clutter data. Results show a clear performance improvement for faster scan rates provided that the number of coherently integrated samples is high enough.
    IEEE National Radar Conference - Proceedings 01/2010;
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    ABSTRACT: Compound models are widely used to describe high resolution radar sea backscatter. In this paper, experimental high resolution sea clutter data is used to assess the validity of the compound Gaussian model for range resolution of centimeters. Results show that the central limit theorem is still applicable to local sea backscatter at very high range resolutions.
    Radar Conference - Surveillance for a Safer World, 2009. RADAR. International; 11/2009
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    ABSTRACT: The authors present a novel and heuristic approach for the detection of low radar cross-section targets in high-resolution sea clutter. The proposed technique is based on the application of the Radon transform to range-time matrices formed by column-wise storage of consecutive range profiles. The objective of this paper is 2-fold: to analyse the effect of the transform on real high-resolution sea clutter and to describe a detection scheme based on the insight obtained. The proposed technique emulates the behaviour of traditional motion target detection algorithms without the need for reliable Doppler information. It also constitutes a powerful non-coherent integration strategy of the target-s energy along its specific path on the range-time plot. The performance of the detection technique has been tested against real high-resolution sea clutter data, acquired at the south coast of Spain with an in-house developed continuous wave linear frequency modulated millimetre-wave radar system. Monte Carlo simulations show a significant improvement over the conventional cell averaging constant false alarm rate schemes.
    IET Radar Sonar ? Navigation 05/2009; · 0.92 Impact Factor
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    ABSTRACT: The Radon transform can be used to implement grid based ldquotrack-before-detectrdquo processors. The approach can be described as a range alignment step followed by non-coherent integration. In this paper, a modification of the conventional direct Radon transform is proposed to coherently integrate the energy of the target. In this way, the noise and clutter contributions to each projection angle can be minimized and the overall performance of the system will improve.
    IEEE National Radar Conference - Proceedings 01/2009;
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    ABSTRACT: Small target detection in sea clutter is a challenging problem. This paper presents a novel and heuristic approach based on the application of the Radon Transform to a set of consecutive range profiles. The performance of the detection technique has been tested with real sea clutter data, acquired with a high resolution CWLFM (continuous wave linear frequency modulated) millimetre-wave radar demonstrator. Results show that performing the detection on the Radon domain makes the detection of very small targets possible while keeping the false alarm rate controlled.
    Radar, 2008 International Conference on; 10/2008
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    ABSTRACT: 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.
    IEEE Transactions on Geoscience and Remote Sensing 07/2008; · 3.47 Impact Factor
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    ABSTRACT: An Inverse Synthetic Aperture Radar (ISAR) obtains images of radar targets by means of an advanced signal processing. The image quality is usually measured by two parameters: resolution and sidelobe level. Sidelobe level is commonly reduced by lineal apodization (or windowing), this signal processing technique is simple but its mayor drawback is resolution loss.
    Radar Systems, 2007 IET International Conference on; 11/2007
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    ABSTRACT: Not Available
    Radar Systems, 2007. RADAR 2007. The Institution of Engineering and Technology International Conference on; 11/2007
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    ABSTRACT: 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)
    Electrotechnical Conference, 2006. MELECON 2006. IEEE Mediterranean; 06/2006
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    ABSTRACT: 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.
    Radar, 2006 IEEE Conference on; 05/2006
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    ABSTRACT: In this work a new approach to extract the experimental fitting parameters of a microwave power FET temperature dependent DC-model is presented. The suggested procedure avoids the possibility of multiple model solutions by eliminating the measurements temperature dependence. This is accomplished by making use of isothermal measurements which in turn are obtained following a simple non-pulsed approach. The proposed technique was applied to a commercial X band MMIC FET power amplifier
    01/2006;
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    ABSTRACT: This paper presents a simple procedure to extract an electro-thermal model for MMIC power amplifiers. The model accounts for the DC and RF performance of MMIC complex structures formed by multiple transistors combined in different amplifying stages. All the steps taken to perform the thermal and electrical experimental characterization to obtain the model are explained. The extracted model was validated by comparing measured and simulated data of a commercial GaAs FET MMIC power amplifier. It was also used to predict the hot spot temperature and position over a wide range of working conditions.
    Gallium Arsenide and Other Semiconductor Application Symposium, 2005. EGAAS 2005. European; 11/2005
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    ABSTRACT: This paper presents a simple procedure to extract an electro-thermal model for MMIC power amplifiers. The model accounts for the DC and RF performance of MMIC complex structures formed by multiple transistors combined in different amplifying stages. All the steps taken to perform the thermal and electrical experimental characterization to obtain the model are explained. The extracted model was validated by comparing measured and simulated data of a commercial GaAs FET MMIC power amplifier. It was also used to predict the hot spot temperature and position over a wide range of working conditions.
    Journal of Catalysis - J CATAL. 01/2005;