Search

Ecosystem functions and services are severely threatened by unprecedented global loss in biodiversity. To counteract these trends, it is essential to develop systems to monitor changes in biodiversity for planning, evaluating, and implementing conservation and mitigation actions. However, the implementation of monitoring systems suffers from a trade‐off between grain (i.e., the level of detail), extent (i.e., the number of study sites), and temporal repetition. Here, we present an applied and realized networked sensor system for integrated biodiversity monitoring in the Nature 4.0 project as a solution to these challenges, which considers plants and animals not only as targets of investigation, but also as parts of the modular sensor network by carrying sensors. Our networked sensor system consists of three main closely interlinked components with a modular structure: sensors, data transmission, and data storage, which are integrated into pipelines for automated biodiversity monitoring. We present our own real‐world examples of applications, share our experiences in operating them, and provide our collected open data. Our flexible, low‐cost, and open‐source solutions can be applied for monitoring individual and multiple terrestrial plants and animals as well as their interactions. Ultimately, our system can also be applied to area‐wide ecosystem mapping tasks, thereby providing an exemplary cost‐efficient and powerful solution for biodiversity monitoring. Building upon our experiences in the Nature 4.0 project, we identified ten key challenges that need to be addressed to better understand and counteract the ongoing loss of biodiversity using networked sensor systems. To tackle these challenges, interdisciplinary collaboration, additional research, and practical solutions are necessary to enhance the capability and applicability of networked sensor systems for researchers and practitioners, ultimately further helping to ensure the sustainable management of ecosystems and the provision of ecosystem services. [ABSTRACT FROM AUTHOR]

A 19‐GHz low‐phase‐noise PLL‐frequency synthesizer is presented in this letter that is intended to be used in a K‐band FMCW radar which requires strict phase noise for detecting a small unmanned aerial vehicle. The 17.9 to 19.5‐GHz PLL includes a Darlington cross‐coupled capacitive‐degeneration VCO which presents higher maximum attainable oscillation frequency (ƒtrans) and larger negative transconductance (gm), thus resulting in low phase noise. Manufactured using the SiGe BiCMOS process, the K‐band synthesizer demonstrates −114 dBc/Hz at 1 MHz offset and −138 dBc/Hz at 10 MHz offset from 19.456 GHz locking carrier frequency. [ABSTRACT FROM AUTHOR]

Leg tracking is an established field in mobile robotics and machine vision in general. These algorithms, however, only distinguish the scene between leg and nonleg detections. In application fields like firefighting, where people tend to choose squatting or crouching over standing postures, those methods will inevitably fail. Further, tracking based on a single sensor system may reduce the overall reliability if brought to outdoor or complex environments with limited vision on the target objectives. Therefore, we extend our recent work to a multiposture detection system based on laser and radar sensors, that are fused to allow for maximal reliability and accuracy in scenarios as complex as indoor firefighting with vastly limited vision. The proposed tracking pipeline is trained and extensively validated on a new data set. We show that the radar tracker reaches state‐of‐the‐art performance, and that laser and fusion tracker outperform recent methods. [ABSTRACT FROM AUTHOR]

Inspection of the railway tracks requires relying on a precise positioning system that accurately determines the location of potential failures and deficiencies. Therefore, measuring the speed and precise location of rail vehicles is essential. Many methods and approaches have been proposed, but most of them lack several conditions that do not allow them to be optimal for this task. In this paper, the authors present a novel method for measuring the speed of a train by means of the time correlation approach, by using 2‐mm wave radar sensors. Additionally, it is also an accurate positioning system because the authors prove that the track has a unique profile, sufficiently characteristic and stable over time, that serves as a distinctive signature, which can be used to locate the vehicle at any point on that track. As a result, this new methodology, combined with a laser profilometer device, can be used as an effective inspection system for cracks or deficiencies in the rails, sleepers, fastenings, bolts etc., locating them precisely on the railway track. [ABSTRACT FROM AUTHOR]

This article presents a deep neural network‐based constant false alarm rate (NNB‐CFAR) detector for simulated high‐frequency surface wave radar (HFSWR) data. A deep neural network is trained to identify fluctuation parameters of each cell of a range‐Doppler power spectrum based on the patterns present in the neighbouring cells. The estimated parameters are then used for calculating a detection threshold with a user‐specified probability of false alarm. To train the network, a realistic model of HFSWR echoes is used for generating a large labelled range‐Doppler image dataset, including many possible clutter scenarios and interfering target echoes. Several CFAR windows are extracted from the training range‐Doppler dataset and used as training data. The neural network is trained to replicate the output of a maximum likelihood estimator based on the reference cells of the CFAR window. The NNB‐CFAR algorithm was then compared to traditional CFAR algorithms by identifying targets in the second set of simulated range‐Doppler images. The probability of detection was also experimentally measured in the context of HFSWR for all algorithms. Results show that the technique can significantly improve detection rates amid strong clutter. [ABSTRACT FROM AUTHOR]

In the urban environment, the radar is easily affected by multipath (MP) returns. The problem of detecting point‐like targets in the urban environment with the existence of resolvable MP returns under the background of heterogeneous clutter is addressed. Two adaptive detectors have been devised with a combination of prior information on the environment and echoes of target. The detectors can use the MP echoes in all MP prediction range cells for detection or in some available paths for signal detection by the available path selection algorithm that eliminates the weak signal propagation paths. Remarkably, the proposed decision schemes exhibit the desirable constant false alarm rate property with respect to the unknown parameters of the heterogeneous interference. The performance assessment, conducted on simulated data in terms of detection probability also in comparison with conventional solutions, highlights the effectiveness of the MP exploitation, while the MP signal is strong and shows the detection performance enhancement potential. [ABSTRACT FROM AUTHOR]

According to the classification of using multiple sensors, the obstacle detection and recognition technology of unmanned driving is summarized, and the main technical means, algorithms, advantages and disadvantages, difficulties and so on are discussed. These methods mainly include lidar and camera fusion, camera and radar fusion and lidar, camera and radar fusion. In addition, some research achievements in this field in recent years are introduced, and some fusion technologies used in this field are briefly analyzed and summarized. [ABSTRACT FROM AUTHOR]

In order to improve the recognition accuracy of construction machinery and equipment and materials in low contrast scenes, a construction machinery material recognition algorithm based on multisource sensor information fusion is proposed. In the paper, the millimeter wave radar is fused with the camera considering its strong penetration ability in rainy and foggy days and dim environments. Firstly, the spatial coordinates of radar and camera are unified by establishing a spatial fusion model of millimeter wave and camera; then the target acquired by millimeter wave is projected onto the image and the detection frame intersection and ratio model is used to generate the region of interest of the camera; finally, the improved YOLOv2 algorithm is used to identify the region of interest, and in the improved idea, the low‐level information is first connected with the high‐level information in multilayer depth. At the same time, a multiscale feature pyramid network structure is used to achieve recognition of objects of different scales. This model effectively reduces interference from other feature categories while improving the recognition efficiency of the system. The algorithm can effectively improve the recognition accuracy of mechanical materials in low‐contrast scenes, as demonstrated by the validation of different scenes. [ABSTRACT FROM AUTHOR]

This study investigates the use of adaptive radar waveforms in performing a multi‐task operation involving the tracking and classification of a single target. The work applies a previously reported hierarchical fully adaptive radar framework and considers a situation in which the target tracking function is performed using a transmit waveform having adaptive pulse repetition frequency, pulse width, bandwidth, and coherent processing interval parameters, while the classification function can be performed using only a fixed radar waveform. Two alternate strategies for selecting the next waveform are then described. The first strategy is focussed on maintaining fixed measurement performance goals in terms of target range and velocity and classification entropy, while the second approach varies these performance goals depending on the target state. Both approaches are examined for simulated datasets at W‐band representing a moving human target, as well as for laboratory measurements of this scenario. The results for both simulation and experiment show the benefits of including adaptive waveforms in performing multiple radar tasks. [ABSTRACT FROM AUTHOR]

This study focusses on the target detection problem in the distributed multiple‐input multiple‐output (MIMO) radar. The observation environment is assumed to be partially homogeneous in one transmitter‐receiver path and simultaneously non‐homogeneous for different paths. By characterising the disturbance signals with a series of auto‐regressive (AR) processes, two parametric detectors based on the Wald test are developed. The first one utilises an iterative scheme to estimate the unknown parameters that were involved in the derivation, and the second one obtains these estimations sequentially. One of the most attractive features of the two distributed MIMO radar detectors is that they can be used in the presence/absence of the training data. More specifically, they can take advantage of the training data to boost the detection performances effectively even if the training data are very limited. The simulation results of several scenarios demonstrate the remarkable detection performances of authors' proposed methods compared with that of the competitors. Furthermore, the amplitude estimation performances of the two detectors are evaluated via the corresponding Cramér–Rao bound (CRB). [ABSTRACT FROM AUTHOR]

To minimise the noise interference in the radar received echoes and optimise the detection issue for a wideband radar system, a novel wideband radar track‐before‐detect detector via Wiener Filter is proposed. The Wiener Filter can effectively remove the noise mixed in the echoes and make the filtered signal consistent with the original signal. After applying maximum likelihood estimation to the echoes, the authors can reconstruct the desired signal required for Wiener filtering by extracting the range information of each scatterer. Then Wiener Filtering is performed on the echo containing noise with the desired signal to complete the denoising. Subsequently, we exploit the correlation between the adjacent echoes for detection. The effectiveness of the detector can be verified by the numerical simulation results of synthetic and real radar data. The proposed detector is superior to the waveform contrast detector, inter‐period correlation processor and modified correlation matrix detector. [ABSTRACT FROM AUTHOR]

Resource allocation is one of the key problems in radar network. A modified particle swarm optimisation (PSO) algorithm is presented here to improve the performance of resource allocation in radar network with large baseline, where multiple tasks with multiple parameters were considered. First, the resource allocation mathematic model for radar network with large baseline was established. Second, based on modified PSO, the resource allocation algorithm is presented and it can simultaneously deal with both discrete and continuous variables. Finally, the simulation experiment is presented to verify the proposed algorithm. The simulation result suggested that the proposed algorithm is feasible and can satisfy the requirement of resource allocation in the radar network. [ABSTRACT FROM AUTHOR]

A joint target detection and tracking method based on plot-track quality evaluation (PTQE-D&T) is proposed here. The presented method consists of three consecutive steps. First, a set of candidate plots is extracted from the Detector and Plot-Extractor, where the plot quality is calculated simultaneously based on multi-dimensional echoes constituting the plot. Then, a track-before-detect (TBD) processor based on dynamic programming (DP) is utilised to jointly elaborate the observations from multiple scans and outputs potential tracks to be confirmed. Finally, a confirmation strategy is introduced via plot-track quality evaluation. Experimental results are provided to demonstrate the effectiveness of the proposed method, where two data sets collected from a ground-based surface-search radar and a ship borne 3D radar are used. Moreover, the proposed PTQE-D&T structure is totally consistent with conventional radar data processing architecture, meaning that it is promising in engineering applications. [ABSTRACT FROM AUTHOR]

Synchronisation of radar systems can be used to suppress interference and enable communication between radars. In this paper, a generalised Kuramoto model is proposed, which can be used to synchronise pulse repetition frequencies of two radars over‐the‐air. The generalised approach allows the adjustment of a sampling factor which influences the convergence of the two pulse repetition frequencies. Furthermore, sampling criteria are derived, which can be used to estimate whether convergence occurs. Finally, it is shown by means of simulation that the model together with the criteria allows to reliably predict convergence and to perform synchronisation. [ABSTRACT FROM AUTHOR]

Pulse-agile radar systems are becoming more prevalent as the demand for adaptive and cognitive systems increases. This focus is motivated by the need for interference avoidance and spectrum sharing. Pulse agility within a coherent processing interval (CPI) or intra-CPI adaption has been shown to cause distortion, which will negatively impact the radar’s performance. This problem can be framed in the context of image processing such that an ideal range–Doppler image is corrupted by some point spread function. Deconvolution is then applied to remove this distortion and improve radar performance while maintaining the ability to use computationally efficient fast Fourier transform-based processing. [ABSTRACT FROM AUTHOR]

In this study, the design and analysis of a seven-port radar duplexer for tracking a target in X-band operation are presented. The S-parameters of the structure are calculated and compared with experimental results. The simulations and experimental results are in good agreement. This device enables radars to calculate the horizontal difference, vertical difference, and sum of four beams of a monopulse antenna based on amplitude discriminator. Three magic-Ts and one Tjunction are used, four input ports are connected to a monopulse antenna and three other ports are output ports. The output data give three equations between input signals that allow the radar to track a target. Results show that the S-parameters of this device are affected by magic-Ts and the T-junction structure, and an optimum structure for the magic-Ts and T-junction is proposed. A comprehensive study has been carried out for determination and comparison of properties of the structure in theory, simulation, and experimental results. This device is useful in radar tracking systems. [ABSTRACT FROM AUTHOR]

Nyquist folding receiver (NYFR) can realize the wideband receiving with a small amount of equipment. As a tradeoff between the amount of equipment and the complexity of the signal processing, the NYFR output is usually a hybrid modulated signal. Therefore, it is necessary to investigate the parameter estimation method of the signal intercepted by the NYFR. Binary phase shift keying (BPSK) signal is a typical low probability of intercept radar signal and the authors focus on the parameter estimation of the BPSK radar signal intercepted by the NYFR. Firstly, matching component function is proposed to obtain Nyquist zone (NZ) index. Then, the Hankel-singular value decomposition (SVD) method is introduced to estimate the code rate of the BPSK signal. The efficacy of the Hankel-SVD method is proved in a mathematical way. Several numerical simulations demonstrate the merits of the proposed approach and finally, a brief investigation for case of the multiple BPSK signals intercepted by the NYFR is given. For NZ index estimation, the computational complexity of the matching component function is low and it has no need to use squaring process. In addition, the code rate estimation using the Hankel-SVD method is more accurate compared with the wavelet transform. [ABSTRACT FROM AUTHOR]

Classical stretch processing (SP) obtains high range resolution by compressing large bandwidth signals with narrowband receivers using lower rate analogue-to-digital converters. SP achieves the resolution of the large bandwidth signal by focusing into a limited range window, and by deramping in the analogue domain. SP offers moderate data rate for signal processing for high bandwidth waveforms. Furthermore, if the scene in the examined window is sparse, compressive sensing (CS)-based techniques have the potential to further decrease the required number of measurements. However, CS-based reconstructions are highly affected by model mismatches such as targets that are off-the-grid. This study proposes a sparsitybased iterative parameter perturbation technique for SP that is robust to targets off-the-grid in range or Doppler. The error between reconstructed and actual scenes is measured using Earth mover's distance metric. Performance analyses of the proposed technique are compared with classical CS and SP techniques in terms of data rate, resolution and signal-to-noise ratio. It is shown through simulations that the proposed technique offers robust and high-resolution reconstructions for the same data rate compared with both classical SP- and CS-based techniques. [ABSTRACT FROM AUTHOR]

Performance bounds on range resolution and range sidelobe level are built for waveforms with spectral notches. In this study, the authors use the integrated mainlobe energy (IME) and integrated sidelobe energy (ISE) of the autocorrelation function to assess the performance of range resolution and range sidelobe level, respectively. By considering the minimisation of the weighted sum of IME and ISE under given spectral constraints, they derive the optimal power spectrum density condition and subsequently calculate the best achievable IME and ISE. With this study, the radar system can (i) analyse the trade-off relationship between range resolution and range sidelobe level and thus better balance them in designing the transmit waveform; (ii) assess the fitness of potential working bands and thus select the best one to use. [ABSTRACT FROM AUTHOR]

This study investigates the effects of antenna rotation on range, radial velocity, and azimuth estimation during coherent integration in linear frequency-modulated continuous wave (LFMCW) radars. When antenna scans during the coherent integration time, theoretical analysis indicates that the angle sensing with the traditional sum-difference amplitude-comparison (SDAC) monopulse method and the range, radial velocity estimation with interpolation method are different from that in staring mode. Simulation demonstrates that the estimation performance is heavily impaired by the antenna rotation. In this study, a generalised mathematical model of coherent integration for LFMCW radar is established. Furthermore, a high-precision estimation method, which consists of generalised SDAC monopulse method, radial velocity estimator with modified interpolation curves, and range estimator refined by Doppler frequency, is proposed. A complete signal-processing scheme is proposed for the accurate estimation of the target parameter in mechanical scanning LFMCW radar. A sub-optimal method is provided for practical implementation. Experimental and simulation results show that the proposed method achieves high accuracy and robustness. [ABSTRACT FROM AUTHOR]

The effects of rain attenuation on communication systems will become more pronounced in future satellite communication systems, especially with the planned use of the 21-GHz band or higher-frequency bands. Diversity techniques provide a solution to mitigate rain attenuation effects. This study proposes a time diversity technique, one such technique that is likely to demonstrate high effectiveness. To model the system, rainfall rate statistics are necessary, and reliability is improved as the amount of statistical data increases. This paper derives the cumulative distribution of the rainfall rate across Japan over 4 years using rain radar data from the automated meteorological data acquisition system and ground-based rain radar network and evaluates the rainfall rate at 23 observation points across Japan. We carry out a performance evaluation for all locations within Japan to confirm the efficiency of the time diversity method. Finally, we propose prediction model of the time diversity gain for Japan and other significant parameter which is time correlation of rainfall rate that was found from the time diversity results for further investigation. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, an ultrathin penta-band polarization-insensitive metamaterial absorber has been presented, which consists of an array of a closed ring embedded in a tetra-arrow resonator. The proposed ultrathin ( ∼λ0/18 corresponding to the highest absorption frequency) structure exhibits five distinct absorption peaks at 3.4, 8.34, 9.46, 14.44, and 16.62 GHz with peak absorptivities of 98.6%, 96.6%, 90.1%, 97.8%, and 93.1%, respectively. Due to fourfold symmetry the structure provides nearly unity absorption for all polarization angles under normal incidence. The structure also exhibits high absorption peaks ( ∼80%) up to 45° incident angles for both TE and TM polarizations. Surface current and electric field distributions for different absorption frequencies have been analyzed to visualize the absorption mechanism of the structure. Finally, the structure has been fabricated and experimentally measured responses are in good agreement with the simulated ones. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2519-2524, 2015 [ABSTRACT FROM AUTHOR]

In high-resolution radar systems, stretch processing technique is generally used to process the returned signals of a range-spread target. Consequently, this results in mixer outputs that consist of several linear frequency modulation components with a small frequency rate (FR). The authors define an FR function to transform a signal from the time domain into the FR domain and discuss the FR range of a discrete signal. Then an interesting phenomenon is found in the FR domain, that is, the mixer output is concentrated in a low FR region, while the Gaussian noise spreads over the entire FR region. Therefore, a range-spread target detector has been proposed that regards the integration of the values in a vicinity of zero FR as the test statistic. This detector uses a single mixer output and thus has the ability to detect the target with a high velocity. Finally, the proposed detector is evaluated by recorded radar data. Experimental results show that the proposed detector outperforms the detectors using the high-resolution range profile. [ABSTRACT FROM AUTHOR]

The adaptive integral method (AIM) in conjunction with the low-rank compression method is developed to calculate the monostatic radar cross-section (RCS) of arbitrarily shaped three-dimensional perfectly electric conducting objects. For backscattering problems, the excitation matrix is usually highly rank-deficient and can be compressed via low-rank techniques without explicitly assembling the original matrix beforehand. Therefore, only the matrix equations corresponding to the linearly independent excitation vectors need to be solved, whose number is much less than that of incident angles. As a result, fast monostatic RCS calculation over a widely angular range can be achieved. To facilitate the analysis of electrical large problems, the AIM is applied to accelerate the matrix-vector product and reduce the memory usage. Numerical examples are presented to demonstrate the validity and efficiency of the method. [ABSTRACT FROM AUTHOR]

Through-wall imaging (TWI) may provide vital information on interior environment in cases when physically entering such environment would pose danger to the person involved.The concept of ultra wideband radar (UWB radar) is an emerging technology, which offers high spatial resolution, as opposed to narrow band radars. Thus, TWI applications using UWB radar have become a growing field of research with several applications in the civil and defense areas such as rescue and surveillance. For this study, a prototype system of UWB radar to TWI has been built. Analyses and result to several kinds of experiments have been presented, that is, detection and visualization of metallic targets behind wooden board wall and concrete blocks wall. The results are encouraging and show the advantages of using UWB radar for TWI. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 54:339-344, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26543 [ABSTRACT FROM AUTHOR]

Autonomous vehicle operations in outdoor environments challenge robotic perception. Construction, mining, agriculture, and planetary exploration environments are examples in which the presence of dust, fog, rain, changing illumination due to low sun angles, and lack of contrast can dramatically degrade conventional stereo and laser sensing. Nonetheless, environment perception can still succeed under compromised visibility through the use of a millimeter-wave radar. Radar also allows for multiple object detection within a single beam, whereas other range sensors are limited to one target return per emission. However, radar has shortcomings as well, such as a large footprint, specularity effects, and limited range resolution, all of which may result in poor environment survey or difficulty in interpretation. This paper presents a novel method for ground segmentation using a millimeter-wave radar mounted on a ground vehicle. Issues relevant to short-range perception in an outdoor environment are described along with field experiments and a quantitative comparison to laser data. The ability to classify the ground is successfully demonstrated in clear and low-visibility conditions, and significant improvement in range accuracy is shown. Finally, conclusions are drawn on the utility of millimeter-wave radar as a robotic sensor for persistent and accurate perception in natural scenarios. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The U.S. Coast Guard, Customs and Border Patrol, Marine Corps, and Navy have deployed several hundred port patrol vessels to protect waterways, U.S. Navy ships and other high-value assets in ports world-wide. Each vessel has an armed crew of four, is relatively fast, and features a surface search radar, radios, and a machine gun. These vessels coordinate surveillance patrols in groups of two or four. We developed a mathematical model for advantageously positioning these vessels, and possibly shore-based radar too, to minimize the probability that an intelligent adversary in one or more speedboats will evade detection while mounting an attack. Attackers can use elevated obstructions to evade radar detection in their attack paths, and ports feature many such restrictions to navigation and observation. A key, but realistic assumption complicates planning: the attackers will be aware of defensive positions and capabilities in advance of mounting their attack. The defender-attacker optimization suggests plans here for a fictitious port, the port of Hong Kong, and the U.S. Navy Fifth Fleet Headquarters in Bahrain. In these cases, the defender can almost certainly detect any attack, even though the attacker, observing defender prepositioning, plans clever, and evasive attack tracks. Published 2011 Wiley Periodicals, Inc.† Naval Research Logistics, 2011 [ABSTRACT FROM AUTHOR]

A millimeter-wave six-port implementation using combined substrate-integrated waveguide (SIW) and microstrip technologies, and low-loss short transition between microstrip and SIW is presented. The six-port is implemented using SIW hybrid couplers with continuous metalized grooves and Wilkinson power dividers. The proposed circuit is suitable for 77-GHz radar sensor front ends. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2488–2493, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25538 [ABSTRACT FROM AUTHOR]

A behavioral model describing the behavior of active mixers in the linear and the saturation mode of operation is presented. The model allows the simulation of effects caused by high-level blocking signals. A 77-GHz multi-tone signal is used for characterizing the nonlinear behavior of the mixer. Because of the calculation of the nonlinearity in the complex baseband, the mixer behavior can be simulated very efficiently as necessary for the usability in complex radar system simulations. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 639–642, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24983 [ABSTRACT FROM AUTHOR]

Information about several topics discussed at the workshop of the International Society for Photogrammetry and Remote Sensing (ISPRS), held at the Leibniz Universität Hannover in Germany from June 2-5, 2009 is presented. Topics include high-resolution earth imaging, optical satellites, airborne digital sensors, and synthetic aperture radars. The workshop featured several speakers including Christian Heipke, David Holland, Clive Fraser.

A low-cost homodyne Doppler radar system with 24.128 GHz phase lock loop (PLL) frequency synthesizer has been designed, fabricated, and applied in remote detection of heart beat. In this direct conversion Doppler radar system, the PLL frequency synthesizer is utilized as a high-stability local oscillator which is realized traditionally by voltage control oscillator (VCO). This fourth-order topology PLL-frequency synthesizer with 8 dBm output power and-67 dBc/Hz at 1 kHz phase noise offset the carrier can improve the radar system velocity precision drastically. The Doppler radar front-end system is fabricated with multichip module technology. Time domain and frequency domain test results of the radar for heart beat detection are both presented in the article, which agree with the reality well. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3139–3142, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23923 [ABSTRACT FROM AUTHOR]

A sparse approximate inverse (SAI) preconditioning of deflated block-generalized minimal residual (GMRES) algorithm is proposed to solve large dense linear systems with multiple right-hand sides arising from monostatic radar cross section (RCS) calculations. The multilevel fast multipole method (MLFMM) is used to accelerate the matrix–vector product operations, and the SAI preconditioning technique is employed to speed up the convergence rate of block-GMRES (BGMRES) iterations. The main purpose of this study is to show that the convergence rate of the SAI preconditioned BGMRES method can be significantly improved by deflating a few smallest eigenvalues. Numerical experiments indicate that the combined effect of the SAI preconditioning technique that clusters most of eigenvalues to one, coupled with the deflation technique that shifts the rest of the smallest eigenvalues in the spectrum, can be very beneficial in the MLFMM, thus reducing the overall simulation time substantially. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]