Software Defined Radar is the latest trend in radar development. To handle enhanced radar signal processing techniques, advanced radars need to be able of generating various types of waveforms, such as frequency modulated or phase coded, and to perform multiple functions. The adoption of a Software Defined Radio system makes easier all these abilities. In this work, the implementation of a Software Defined radar system for target tracking using the USRP platform is discussed. For the first time, an experimental characterization in terms of radar application is performed on the latest USRP NI2920, demonstrating a strongly improved target resolution with respect to the first generation platform.
High-performance dual-band Doherty power amplifier and non-uniform circularlypolarizedantenna array require impedance-transformingunequal dual-band 90° branch-line couplers forpower dividing and phase shiftingin the feed networks.In this paper, an analytical design methodology of generalized impedance-transforming dual-band branch-line couplers for arbitrary coupling levels is proposed. The coupler features wide range of realizable frequency ratio, multiple flexibleselections of open- or short-circuited and pi- or T-network topologies. For demonstration, four numerical examples with different parameters are presented.Furthermore, two microstrip couplers based on open-circuited pi- and T-network topologies were fabricated and measured.The measured results show good performance at dual 1.8/3.45 GHz bands.Thefractional bandwidthsdefined by the fluctuation of the coupling level and the phase difference less than ±0.5 dB and ±5°are up to 17% and 18%, 18% and 2% for open-circuited pi- and T-network topologies, respectively.
An equivalent circuit based on propagating and evanescent accessible modes is discussed and the numerical values of its elements (susceptances and electrical length) are obtained starting from the knowledge of the generalized scattering matrix S of microwave discontinuities. A database of the circuit elements is then defined in the frequency and geometric ranges of the analyzed discontinuities and is used to evaluate the generalized scattering matrix for values not contained in the database, with very simple formulas for any number of circuit ports. The obtained S matrices can be used to analyze very complex structures such as iris-based filters and manifold filters.
In multi-input multi-output (MIMO) radar transmit beampattern synthesis, most current literature formulates the problems in steradian space. However, since the beampattern and its parameters are both measured and defined in radian space, from the view point of physical meaning, it will be better to reformulate the problems in radian space rather than in steradian space. In this paper, we propose methods in the radian space to synthesize beampatterns based on minimizing sidelobe level for the two main designs in MIMO radar, i.e. minimum sidelobe beampattern design (MSBD) and beampattern matching design (BMD). For MSBD, the design criteria considering both peak sidelobe level and integrated sidelobe level is proposed. By this we can have a good tradeoff between the intensity and power distribution in beampattern synthesis. After a two-step converting, the formulation of the criteria is transformed into a convex programming, where a global optimal solution can be obtained. For BMD, instead of minimizing mean square error directly as in conventional methods, we propose a power-approximation-based method by minimizing integrated sidelobe level. Finally, numerical comparisons with classical methods demonstrate that the proposed MSBD maintains for all range of main lobe width and the proposed BMD has smoother main lobes with maximal power focused in.
This paper proposes an imaging scheme using a random sparse array (RSA) structure for radar target detection using compressed sensing (CS). The array collects sparse measurements with less collection time and data storage. Two schemes of the RSA are considered, random SAR mode and random array mode. Performances of both static and moving target detections are investigated. Performance of RSA with CS is compared with that using full SAR data with conventional back-projection (BP) method for static target detection and full uniform linear array (ULA) data with conventional beamforming (CBF) method for moving target detection. Simulation and real experimental tests are provided to verify the proposed target imaging scheme. Results show that RSA imaging with CS can perform better than normal SAR and ULA with conventional imaging methods. However, when environment is complicated and background too noisy, CS may have degraded performance.
A simple and analytical design methodology for a novel multi-way Bagley Polygon power divider with arbitrary complex terminated impedances is proposed in this paper. The design parameters including electrical lengths and characteristic impedances can be obtained by the provided closed-form mathematical expressions when complex terminated impedances are known. Moreover, for convenient test, we design an impedance transformer to transform the complex impedance into real impedance using an extension line, and especially a reflection coefficient chart to solve it. Four special cases of 3-way Bagley Polygon power divider operating at 2.4 GHz are fabricated and measured with different condition complex terminated impedances for the purpose of verification. Excellent agreement between simulation and measurement results proves the validity of the design method. The presented Bagley Polygon power divider exhibits 180° phase difference between any two adjacent output ports and 0° phase difference between two symmetrical output ports and is suitable for multi-antenna and differential antenna system. Furthermore, simple layouts lead to convenient design procedure and easy fabrication.
The paper aims to investigate the use of the Finite Element Method for electrical and mechanical faults detection in three-phase squirrel cage, induction machines. The features of Finite Element Method are significant, which consider the physical mapping of stator winding and rotor bar distribution. Therefore, modeling of the faults in stator winding, rotor bars and air-gap eccentricity will be predicated in more accurate way. In comparison with conventional methods such as coupling method, the Finite Element Method considers the complex machine geometry, material type of the bar, current and the flux distributions within the electrical machines. As a result, the air-gap eccentricity and the broken bars can be modeled effectively using this approach. Motor current signature analysis has been used to give a decision about the fault occurrence. For the broken rotor bar, frequency of the sideband components around the fundamental is used to indicate the presence of fault. However, the sideband frequencies cannot be used to recognize the stator winding short circuit and eccentricities faults, where the harmonics have approximately the same frequency over the spectrum. The amplitude of the sideband harmonic components have been used to differentiate between them. It has been found that the inter-turn short circuit faults have a sideband harmonic component with amplitude greater than that in the case of the air-gap eccentricity faults. Also current paper introduce the detection of broken rotor bars based on stator current envelope technique.
In this paper, we propose a multi-beam model for antenna array pattern synthesis( AAPS) problem. The model uses a conic trust region algorithm (CTRA) similarly proposed in this paper to optimize its cost function. Undoubtedly, whole algorithm efficiency ultimately lies on the CTRA, thereof, we propose a method to improve the iterative algorithm's efficiency. Unlike traditional trust region methods that resolve sub-problems, the CTRA efficiently searches a region via solving a inequation, by which it identifies new iteration points when a trial step is rejected. Thus, the proposed algorithm improves computational efficiency. Moreover, the CTRA has strong convergence properties with the local superlinear and quadratic convergence rate under mild conditions, and exhibits high efficiency and robustness. Finally, we apply the combinative algorithm to AAPS. Numerical results show that the method is highly robust, and computer simulations indicate that the algorithm excellently performs AAPS problem.
Design of multi-element antennas (MA) for small mobile terminals operating at higher frequencies remains challenging despite smaller antenna dimension and possibility of achieving electrically large separation between them. In this paper, the importance of the type of radiating elements operating at 3400-3600 MHz and their locations on the terminal chassis is highlighted. An isotropic radiation pattern that receives incoming signals from arbitrary directions is obtained by combining the radiation patterns of multiple antennas with localized chassis current distribution. Four MA configurations with two- and eight-element antennas are designed and evaluated experimentally in indoor propagation environments. Our proposed designs of MAs provide the highest MIMO channel capacity compared to their counterparts using antennas with less localized chassis current distribution, even in the presence of user's hand.
Just over a decade ago, wireless capsule endoscopy (WCE) was introduced as a novel alternative to conventional wire or probe endoscopy to examine disorders of the human gastrointestinal (GI) tract. Yet, the persistent inability of transmitting high-quality images due to limited data rate of the telemetry system continues to be an issue of major concern. Thus, high-data-rate telemetry systems are essential due to the widespread use of the WCE technique. In this paper, we present such a telemetry system that includes a highly-simplified receiver for the use in WCE. Unlike the conventional architecture of a radio frequency (RF) receiver, the architecture of the new receiver allows the direct conversion of analog RF signals to digital signals, eliminating the need for any frequency conversion in the analogue domain. Our receiver system consists of sub-blocks, a low-noise amplifier (LNA), a logarithmic amplifier (LA), a power detector (PD), and a comparator. The common-source cascode LNA was designed with its frequency spectrum centralized at 450 MHz, which was determined by electromagnetic (EM) simulation of the path loss in the GI tract of the human body. To ensure that the higher data rate, i.e., 100 Mbps, could be attained, the LNA was designed for a system bandwidth of 100 MHz, i.e., 400-500 MHz. The LNA and the three cascading blocks in combination have total gain of 80 dB to compensate for the losses in the weak signals that are received. The LNA and the LA, including the PD and the comparator, require 17-mA and 337-μA currents, respectively, from a 1.5-V, DC source.
This paper presents a compact dual-band multiple input multiple output (MIMO) antenna with low mutual coupling, operating in the 2.4 GHz band (2.4-2.485 GHz) and 5.5 GHz band (5.15-5.85 GHz). The proposed antenna system consists of two antenna elements located at the top two corners of FR4 substrate (PCB). Each element dimension is reduced substantially by employing a folded structure and slots on the top patch plate, so that it takes up a small volume of 12 × 9 × 6 mm3. To enhance port-to-port isolation and efficiency of each antenna, an additional non-radiating folded shorting strip is connected between each antenna element and ground plane of PCB. The measured isolation values are lower than -28 dB over the lower WLAN band (2.4-2.485 GHz) and better than -26 dB (-30 dB in most of the band) across the higher WLAN band (5.15-5.85 GHz). The improvement in antenna's efficiency caused to raise up 1 dB of effective diversity gain of MIMO system. Furthermore S-parameters, radiation patterns and diversity performance characteristics are provided.
An accurate and efficient SAR raw data generator is of considerable value for testing system parameters and the imaging algorithms. However, most of the existing simulators concentrate on the raw signal simulation of the static extended scenes and targets. Actually the raw signal simulator of the moving targets is highly desired to quantitatively support the application of the ground moving targets indication. The raw data simulation can be exactly realized in the time domain but not efficient especially when simulating an extended scene. As for the issues, the analytical expression for the 2-D signal spectrum of moving targets with constant acceleration is derived and a fast raw data simulation method in the 2-D frequency domain based on inverse ω-k algorithm is proposed in this paper, where the inverse STOLT interpolation is applied to simulate the range-azimuth couple. So it is more efficient than the time domain one by making use of Fast Fourier Transform (FFT). Simulation results for a man-made scene and a real SAR scene are provided to demonstrate its validity and effectiveness.
We generalize Wheeler-Feynman electrodynamics with a variational problem for trajectories that are required to merge continuously into given past and future boundary segments. We prove that the boundary-value problem is well posed for two classes of boundary data and the well-posed solution in general has velocity discontinuities, henceforth a broken extremum. Along regular segments, broken extrema satisfy the Euler-Lagrange neutral differential delay equations with state-dependent deviating arguments. At points where velocities are discontinuous, broken extrema satisfy the Weierstrass-Erdmann corner conditions that energies and momenta are continuous. Electromagnetic fields of the finite trajectory segments are derived quantities that can be extended to a bounded region B of space-time. Extrema with a finite number N of velocity discontinuities have extended fields defined in B with the possible exception of N spherical surfaces, and satisfy the integral laws of classical electrodynamics for most surfaces and curves inside B. As an application, we study the hydrogenoid atomic model with mass ratio varying by three orders of magnitude to include hydrogen, muonium and positronium. For each model we construct globally bounded trajectories with vanishing far-fields using periodic perturbations of circular orbits. Our model uses solutions of the neutral differential delay equations along regular segments and a variational approximation for the head-on collisional segments (spikes). Each hydrogenoid model predicts a discrete set of finitely measured neighbourhoods of periodic orbits with vanishing far-fields right at the correct atomic magnitude and in quantitative and qualitative agreement with experiment and quantum mechanics. The spacings between consecutive discrete angular momenta agree with Planck's constant within thirty-percent, while orbital frequencies agree with a corresponding spectroscopic line within a few percent.
Precise modeling of radio propagation is necessary for experiencing the benefits of wireless technology for indoor environments. Among many modeling techniques, the ray tracing based prediction models become popular for indoor wireless radio propagation characterization. Though the ray tracing models are popular, their key deficiency is the slower performance. In this paper, an accelerated technique for three dimensional ray tracing using Adelson-Velski and Landis (AVL) tree data structure is introduced. Here, the AVL tree data structure is coupled with the concepts of quadrant eliminating technique (QET) and nearest neighbor finder (NNF) for optimization and fast characterization of indoor wireless communication. Surface intersection scheme (SIS) is also introduced for optimizing the ray-object intersection time. The AVL tree is used for the effective handling of the objects and environments relative information. The QET technique decreases the ray tracing time by omitting unnecessary object, while NNF decreases the ray-object intersection time by finding the nearest object in an efficient technique. For the validation of the superiority of the proposed technique, a detailed comparison is made with the existing techniques. The comparison shows that the proposed technique has 81.69% lower time consumption than the existing techniques.
During the last decade, selective photonic crystal filters have received much research interest in the fields of nanotechnology and optical interconnection network. The main focus of this paper consists of an analysis and a synthesis of one-dimensional photonic crystal selective filters. The optimization is performed by employing the simulated annealing algorithm. The filters synthesis is obtained by acting on the Bragg grating layer widths. Simulated annealing is applied to solve the PhC-1D filters synthesis problem in order to reduce the quadratic error and to obtain a desired transmission according to a Gaussian function defined in advance by the user. Starting from the Maxwell's equations for dielectric nonmagnetic structure, we show the derivation of the Helmholtz equation and find its solution for 1D layered structure. In addition, the boundary conditions and equation transformation to set of linear equations which are solved using Cramer‟s method are described thoroughly. This mathematical technique is then applied for computation of the transmission spectra of 1D perfectly periodic structure and structures with different defects. These results can be easily applied for design of selective filters.
A highly efficient asymmetrical GaN Doherty power amplifier using traditionalλ/4 transmission line and an asymmetrical GaN Doherty power amplifier(DPA) using composite right/left-handed transmission lines(CRLH-TL) for linearity improvement are presented in this paper.The CRLH-TL is designed to suppress the second harmonic of the output of the carrier amplifier. This DPA using CRLH-TL is designed for 3.5 GHz LTE-Advanced Application with 100 MHz bandwidth and 37 dBm average output power, the carrier and peaking amplifiers are fabricated with the same 30 W GaN HEMT and unevenly driven in purpose of maintaining high efficiency at back-off power (BOP) region. At 9-dB and 6-dB BOP, the DE achieves 30% and 40.1%, respectively, and the adjacent channel power ratio(ACPR) are less than-37.1 dBc for 40 MHz 16 QAM signal at 37 dBm. In addition, the further linearization of the DPA is realized by using digital pre-distortion(DPD), the ACPRs are improved to-49.6 dBc for 40 MHz 16 QAM signal.The measured results show linearity improvement compared with the traditional DPA.
A technique for magnetic resonance brain image classification using perceptual texture features, fuzzy weighting and support vector machines is proposed. In contrast to existing literature which generally classify the magnetic resonance brain images into normal and abnormal classes, classification with in abnormal brain which is relatively hard and challenging problem is addressed here. Texture features along with invariant moments are extracted and the weights are assigned to each feature to increase classification accuracy. Multi-class support vector machine is used for classification purpose. Results demonstrate that the classification accuracy of the proposed scheme is better than the state of the art existing techniques.
Cooperative wide-band spectrum sensing has been considered to enable cognitive radio operation of wireless regional area networks (WRAN) in the UHF and VHF TV broadcasting bands. In this paper, cooperative compressed spectrum sensing is considered to enable fast sensing of the wide-band spectrum. The speed and accuracy of spectrum sensing are improved by further optimization of the compressed sensing receiver, which is done blindly without any prior knowledge of the sensed signal. Enhanced compressed spectrum sensing algorithms are proposed for the cases of individual spectrum sensing and cooperative spectrum sensing (CSS). The cooperative signal reconstruction process is modified to optimally combine the received measurements at the fusion center. A low complexity authentication mechanism, which is inherent to cooperative compressed spectrum sensing, is proposed to make the cognitive radio system immune to adversary attacks.
This article describes a time-domain transmission line model based on distributed parameters for transient analysis. This model is based directly on the differential equations for the basic transmission line without any previous simplification. The solution presented here for these differential equations results in a more detailed time-domain model than others models currently in use, and with certain structural similarities with the distributed parameter frequency-domain model for long transmission lines. The deduction of a general time-domain transmission line model for fundamental frequencies parameters and single-phase line are presented in this article, but the model can also be extended to cases with multiconductor and frequency-depended parameters. In order to validate the model, a comparative test is presented to facilitate the analysis about the main similarities and differences between this and other models.
The synthetic aperture radar (SAR) is a widely used instrument for high-resolution imaging from aircraft or satellite platforms. In the paper, the problem of the defocusing of multi-look SAR images by uncompensated phase errors presented in the received data is analyzed. It is shown that the phase errors on a multi-look processing interval can be effectively described in terms of local quadratic and local linear phase errors. Approximate analytical expressions are derived to describe the azimuth resolution degradation. Criteria for acceptable phase errors are given. The obtained results are verified by numerical simulations. The approach is illustrated by two typical motion errors: slow deflections of a SAR platform trajectory from a reference flight line and periodic trajectory deviations.
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