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It is well known that accurate estimation of the loop delay between the input and output feedback signals is the key to behavioral modeling and digital predistortion of power amplifier. Nevertheless, most of the traditional loop‐delay compensation algorithms have the disadvantage of high computational complexity. For the purpose of solving this problem, a loop‐delay estimation algorithm based on sliding window has been proposed in this paper, where the first derivative characteristic of the signal is employed to evaluate the correlation between the input and output feedback signals. The simulation and experiment are carried out with different bandwidth signals in this paper. The results show that the proposed algorithm and the traditional cross‐correlation‐based method could align the input and output feedback signals successfully. But in terms of resource consumption, the proposed algorithm could reduce the multiplier nearly by 100% and the adder by approximately 93.2%. [ABSTRACT FROM AUTHOR]

In this paper, a novel algorithm based on logistic regression digital backpropagation (LR‐DBP) is proposed to mitigate the effect of dispersion and nonlinearity in a long‐distance optical transmission system. The LR‐DBP can evaluate nonlinear effects by estimating the cross‐entropy error and adjusting the structure of DBP. The experiment is setup to demonstrate an 80 Gbit/s 16QAM signal transmitted across 1000 km single‐mode fiber. The results show that LR‐DBP achieves a 1.8 dB launch power improvement over the dispersion compensation algorithm and a 0.6 dB launch power gain with DBP. The proposed algorithm could obtain with 19.2% computational complexity decrease and 19.6% central processing unit (CPU) running time decrease by calculating the average numbers of real multiplications and CPU running times. [ABSTRACT FROM AUTHOR]

The traditional infrared inspection of substations is usually done by employees with handheld infrared equipment, but the traditional inspection efficiency is not high, and some of the inspection locations have harsh environments, high voltage levels, and high‐risk factors. Given the above problems, this paper proposes an improved defect detection algorithm for substations based on YOLO v7 to solve the difficult problem of infrared inspection of substations. First, the lighter SE‐GhostNetV2 feature extraction network is designed to reduce the computation volume; second, the de‐weighted BIFPN structure is designed for the substation infrared image features to improve the ability of information interaction; finally, the new C‐NWD Loss is proposed to realize the detection of smaller substation equipment and reducing missed detections. The experimental results show that the hybrid accuracy of the algorithm designed in this paper is improved from 92.1% to 96.6%, the model parameters are reduced by 40.1%, the computation amount is reduced by 65%, the detection speed is improved by 87 FPS, and the false detection and missed detections is less, which can achieve real‐time infrared inspection of substations and solve the difficulties existing in traditional substation infrared detection. [ABSTRACT FROM AUTHOR]

Ultra‐wideband (UWB) radar imaging is widely used in penetration detection, target location and detection, and vital monitoring because of its high interference immunity and excellent target recognition with high resolution. In this paper, we report the design of a UWB stepper radar imaging system by using a vector network analyzer and a specially designed novel Vivaldi antenna for far‐field imaging applications. An anti‐attenuation backward projection (AA‐BP) algorithm is proposed to alleviate the attenuation impact of electromagnetic wave propagation. The AA‐BP algorithm and the specially designed Vivaldi antenna are jointly applied in our experiments on multiple targets through wall imaging in both free space and multiple‐path propagation environments. The experimental results show that our reported imaging system achieves desirable performances of far‐field imaging. [ABSTRACT FROM AUTHOR]

The quiet zone of compact antenna test range (CATR) is typically required as uniform as possible with a low phase deviation error. Here, we propose a novel phaseless CATR characterization method by combining a single millimeter‐wave metasurface lens‐based technique and an alternating projection algorithm. The metasurface lens provides two sets of weakly correlated amplitude‐only data to the algorithm by changing the propagation path of the pseudo‐plane wave, hence realizing the phase retrieval of the quiet zone with low complexity of measures. In addition, initial phase preprocessing is adopted to further improve the precision of phase retrieval. Furthermore, different alternating projection algorithms are compared to validate the effectiveness of the proposed method, showing the maximum phase error in the effective quiet zone reaches 0.75° at 220 GHz. In the end, the simulation results show that the proposed method can be applied in the ultra‐broadband frequency range of 120 GHz. In a nutshell, this paper provides new insights for the applications of metasurface lens in the phaseless characterization of CATR. [ABSTRACT FROM AUTHOR]

This paper presents a method for locating electromagnetic sources with an optimized number of measurements by using Independent Component Analysis method. This method can detect the Direction of Arrival (DoA) of sources in special cases such as application of equal number of sensors and sources and detection of sources placed one behind another (overlapped). Simulations and measurements were performed to evaluate the performance of the presented method as well as the comparison to MUSIC and ESPRIT classical algorithms. The ICA method does not only estimate the number of sources, but also has the capability to correlate the DoA of the estimated signal to its source. The advantages and disadvantages of the three methods show the high potential application of the ICA as DoA algorithm. [ABSTRACT FROM AUTHOR]

Multipath interference can be removed from constant envelope signals using adaptive channel equalization based on the constant modulus algorithm (CMA). To be useful in a vehicular mobile radio system, adaptation must occur rapidly by using uncomplicated and cost-effective hardware. This paper will present a new multiplier-less filter structure based on logarithmic algebra with anticipated savings in computational complexity. This paper will discuss the filter application for analogue FM multipath reduction. The simulated distortion is observed to be consistent with that of published measurements. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 1–3, 2003 [ABSTRACT FROM AUTHOR]

Ludwig's algorithm is an algorithm that is widely used in physical optics method. However, the problem of singularity always exist both in the original Ludwig's algorithm and the Ludwig's algorithm based on triangular mesh. Because of this, the problem of singularity is studied further in this paper and a more logical solution to the problem is presented. The validity of the solution given can be seen from the numerical results. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 400–403, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22168 [ABSTRACT FROM AUTHOR]

A new combination of particle-swarm optimization (PSO) and the least-squares support vector machine (LS-SVM) technique for FDTD time-series forecasting is presented. In this paper, the PSO is extended to optimize the hyperparameter used in the LS-SVM algorithm. The numerical simulations demonstrate that the PSO method can efficiently obtain the optimal value of the hyperparameter used in the LS-SVM algorithm. And the PSO_LS-SVM method can improve the computational efficiency of the FDTD algorithm, as compared to the direct FDTD method. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 141–144, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21288 [ABSTRACT FROM AUTHOR]

This paper shows a practical application of genetic algorithms (GAs) for compensating the local magnetic perturbation produced by a ship, while moving in the earth's magnetic field. The compensation is achieved by modifying the number of turns and the current magnitude across the so-called degaussing coils distributed along the ship. A GA scheme for automatic optimisation of these parameters is used. A new objective-function strategy, called a boundary method, is proposed. It is shown that the convergence of the GA is greatly improved when the new objective function is used. Different selection mechanisms, objective function strategies, and scaled methods are revised in this paper. The results show that GAs can be efficiently used to reduce drastically the magnetic field levels of real practical ships. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 281–287, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21147 [ABSTRACT FROM AUTHOR]

This paper presents a simple approach to determine the time-step size required in the alternate-direction-implicit finite-difference time-domain (ADI-FDTD) method in order to obtain a desired numerical dispersion accuracy. The Courant number, the desired dispersion accuracy, and the maximum mesh size Δmax = max(Δx, Δy, Δz) are governed by the numerical dispersion relation, which can be solved by a simple root-finding algorithm to evaluate the Courant number and hence the time-step size for a given mesh size and accuracy. The time-step size is independent of the aspect ratio. To determine if ADI-FDTD is more efficient than the Yee's FDTD, this paper provides a simple relation to evaluate the relative Courant–Friedrich–Levy number (CFLN) from the Courant number and the aspect ratio. The ADI-FDTD method is more efficient than Yee's FDTD when the aspect ratio is high or the mesh density is very large. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 487–490, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20012 [ABSTRACT FROM AUTHOR]

In this paper, we present a far-field pattern calculation technique in the body-of-revolution finite-difference time-domain (BOR–FDTD) method. Because the BOR–FDTD solves two- and half-dimensional problems, it has different features from the three-dimensional FDTD method in the far-field pattern calculation. A monopole antenna fed by a coax is used to validate the technique described in this paper. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 47–50, 2001. [ABSTRACT FROM AUTHOR]

The wavelength-routing assignment (WRA) task for optical networks usually calls for massive computer resources. This paper shows that the economic disadvantages of WRA demands may be solved through the use of an ingenious modification of some complex algorithms and a widely available platform, such as Maple. This paper also shows that a conventional PC can solve, in a few minutes, the disadvantage of the need for powerful workstations, sometimes running in an overnight task. The routines described here can assign wavelengths to a DWDM optical network by using either a minimum route delay procedure or a minimum number of wavelengths per branch alternative. Case studies are presented where solving time and scalability issues are discussed. It is seen that the presented algorithm is an easily reproducible one, and uses widely available tools. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 406–410, 2001. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel structure using different code system division multiple access (DCSDMA) for an optical communication system and a design algorithm to increase the system capacity. This DCSDMA system can transmit two kinds of code systems (for example, the prime code of 7 and 3, respectively). This multicode architecture can improve the theoretical system capacity from P72 to P72+5∗P32. In this paper, we propose an optimal design method to find the simultaneous capacity X%∗72+Y%∗5∗32. X% and Y% are the successful percentages determined by the simulation results. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 291–295, 1999. [ABSTRACT FROM AUTHOR]

In this paper, a technique to steer the array nulls for planar arrays by controlling only the excitation current amplitudes based on genetic algorithms is investigated. The proposed technique is found to be capable of steering the array nulls to the prescribed interference directions with prescribed null depth and simultaneous sidelobe level minimization. In addition, the technique is simple, easily implemented, and versatile compared with other analytic methods for this problem. To verify the validity of the technique, illustrative examples for both rectangular and circular planar arrays are demonstrated. Numerical results show that for planar arrays, even with large elements for cases of a large number of interferences, the proposed technique does succeed in steering the array nulls with satisfactory nulling performance, as desired. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 97–103, 1997. [ABSTRACT FROM AUTHOR]

In this paper, a cost‐effective and simple full duplex RoF (radio over fiber) system is developed from a simplex coherent RoF. At the transmitter, utilizing the magnitude and phase of the vector carrier, four different information are encoded simultaneously on the carrier light wave. Dividing the total carrier power into two branches, enable the transmitter to modulate two distinct information on each branch. The working of the system is described in two main sections namely uplink section and downlink section. In the first section, encoding of uplink transmitting information and decoding downlink information at the central office (CO) is described. In the second section, modulating downlink transmitting information and demodulating coherently the uplink receiving information at the base station (BS) are described. An algorithm based on fast Fourier transform is described for effectively canceling the phase noise (PN) at the BS. Considering the cost of optical components, the source used to coherently detect the uplinked transmitted information, is again used as the carrier for downlink. Altogether, this system enables to transmit three different information on uplink and are faithfully received at the BS with an average of log(BER) value −23 dB. And for downlink, one information is transmitted and is successfully received at the CO with log(BER) of −9 dB. About 10 dB decrease in log(BER) values was found after the cancellation of PN. [ABSTRACT FROM AUTHOR]

The feed model is very important for microstrip antenna analysis using FDTD. In this paper, the feed model with coaxial probe is accurately and efficiently analysed in terms of the contour path technique, driving out the magnetic field modified equations and accomplishing the FDTD procedure. Finally, the characteristic parameters of a cylindrical patch antenna are predicted. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 406–408, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10932 [ABSTRACT FROM AUTHOR]

In this paper we discuss a number of UHF/RFID tag designs including the hybrid loop (Chen and Hsu, International Symposium on Antennas and Propagation, Korea, Vol. 3, 2005, 1045–1048), dual crossed-dipoles, the dual crossed-dipoles utilizing an inductively coupled feed (Choo and Ling, Electron Lett 39 (2003) 3080–3081). We have carried out extensive parametric studies in the process of analyzing the characteristics of the earlier-mentioned antennas, and have investigated several techniques (Choo and Ling, Electron Lett 39 (2003) 3080–3081), including meandering, for size-reduction of these antennas. A design methodology based on the Genetic Algorithm (GA) is presented for the optimization of conformal antennas with Electromagnetic Bandgap (EBG) surfaces (Mittra, Proceedings of International Symposium on Antennas and Propagation 2005 (ISAP2005) Seoul, Korea, 2005, 325–328; Sievenpiper et al., IEEE Trans Microwave Theory Tech 47 (1999), 2059–2074) to improve the antenna performance. The EBG characteristic is realized by utilizing a Frequency Selective Surface (FSS) placed above a thin dielectric substrate backed by a metallic ground plane to act as an Artificial Magnetic Conductor (AMC). The antenna is then placed above the EBG surface to create a conformal integrated EBG - antenna. The initial design of the AMC is carried out by synthesizing a surface whose reflectivity is “+1”, for a normally incident plane wave. However, since the antenna situated above it produces not just a single plane wave but a spectrum of these waves, it becomes necessary to refine the initial design to optimize the performance of the antenna/AMC composite, and techniques for doing this are discussed in the paper. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 858–867, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22265 [ABSTRACT FROM AUTHOR]

In this paper, a parallel algorithm based on MPI (Message Passing Interface) parallel computing library for the finite element method is presented to analyze three-dimensional electromagnetic devices. The algebraic domain decomposition method is used in the algorithm. The original problem is decomposed into several subproblems according to its features. Each of them is allocated to one process in one computation node and solved independently with a direct method. The data are exchanged by communication between adjacent subdomains with overlapped data based on the MPI network. The example of its application is given. Numerical shows that the proposed algorithm can get excellent performance vs. price ratio and can save much memory and CPU time than sequential computing. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 686–692, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22247 [ABSTRACT FROM AUTHOR]

In this paper, a simple and efficient method based on the differential evolution algorithm (DEA) is applied to the problem of modeling nonlinear characteristics of microwave intensity-modulated laser diodes used in a radio-over-fiber (RoF) network. The performance of the presented method is experimentally evaluated using two different laser diodes. Very good agreement between the experimental measurement data and the model output indicates that the presented DEA based method may efficiently be used for accurate modeling and computation of IMD3 power levels of microwave intensity-modulated GaAlAs diodes. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1130–1133, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21560 [ABSTRACT FROM AUTHOR]

This paper describes a technique for synthesizing an equivalent circuit for a broadband antenna. A method is proposed for generating a rational function approximation with real coefficients in order to model the input impedance of the antenna in the frequency domain. An algorithm is then developed to find the best-fit positive-real rational function that is realizable by passive circuits. The technique is applied to a planar UWB antenna from 3 to 10 GHz. The results show that a modeling error of 0.59% can be achieved. The Brune's theorem is used to synthesize an equivalent circuit of the antenna. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 950–953, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21529 [ABSTRACT FROM AUTHOR]

This paper presents a method of moments (MoM) formulation for large thin-wire structures. In our approach, a modified version of the well-known Rao–Wilton–Glisson (RWG) basis functions for wires including a linear phase term is considered. This additional term allows an efficient representation of the travelling-wave modes on each wire, while it preserves the main advantages of RWG bases for arbitrarily complex wire topologies. The paper contains a detailed description of the algorithm used for the computation of the impedance matrix integrals. Finally, some results for scattering problems are presented to show the agreement with the conventional RWG-MoM solution. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 960–966, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21533 [ABSTRACT FROM AUTHOR]

This paper investigates a wire-grid model for the scattering analysis of bodies using the method of moments (MoM). The accuracy of the model is explored in terms of basis functions, and the size and radius of the segments of the model are determined through a defined error function. The numerical simulations indicate that the wire-grid model can accurately calculate the scattering problems when the proper model and the triangular basis function in the MoM are used. The optimal radius of the segments in the model is determined. However, the MoM with the sinusoidal basis function used in NEC2 results in very high error if both large size and large radius are adopted for the segments. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 259–263, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20960 [ABSTRACT FROM AUTHOR]

In this paper, a 3D alternating-direction implicit finite-difference time-domain (ADI-FDTD) algorithm is used to analyze planar circuits. The source excitation in ADI-FDTD is described and two kinds of absorbing boundary conditions (ABCs) are jointly employed for ADI-FDTD algorithm: the Gedney's uniaxial PML scheme is applied in the propagation direction, and Mur's 1st-order absorbing boundary condition (ABC) is set on the other outer surfaces. Both time-domain waveforms and S-parameters are presented. The numerical simulations of several examples show that the number of iterations with this ADI-FDTD algorithm can be six times less than that with the conventional FDTD without a large loss of accuracy. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 175–179, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20936 [ABSTRACT FROM AUTHOR]

In FDTD simulations, the excitation sources can be divided into two categories: (i) the displacement-current source, which is generated by a time-varying electric field; (ii) the induced-current source, which exists in the lossy material. Currently, the latter source is the popular choice in most FDTD simulations. However, there are two problems with the use of this source: the time signal shape at the observation points is different from that of the input pulse, and an artificial DC component is introduced into the solution that prevents the solution from converging to zero. The objective of this paper is to investigate these excitation sources and to clarify some concepts in FDTD simulations. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 203–207, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20770 [ABSTRACT FROM AUTHOR]

Previously, the regular Fourier pseudospectral time-domain (PSTD) algorithm was recognized as mainly applicable to simulations of low-contrast dielectric materials. In this paper, we discuss the difficulties in simulating high-contrast and particularly metallic materials using the Fourier PSTD method. To overcome these difficulties, we use a nonuniform grid obtained from a specially designed mapping curve that can reduce the Gibbs phenomenon in the mapped space. The convergence property of this technique is then examined. We show dramatic improvements compared with regular Fourier PSTD and finite-difference time-domain (FDTD) methods on a uniform grid. As an example application, we apply our method to the modeling of the 2D scattering of a chrome-projection lithography mask. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 569–575, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20699 [ABSTRACT FROM AUTHOR]

The design of frequency-selective surfaces (FSSs) with double-square-loop patch elements using the differential evolution strategy coupled with an equivalent circuit model (ECM) is proposed in this paper. A very efficient optimization algorithm, the differential evolution strategy is employed to tune the FSS unit-cell dimensions. In the fast computational method, the equivalent-circuit model is also employed to analyze the electromagnetic scattering from the FSS screen. The simulated results are in good agreement with the measured results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 159–162, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20575 [ABSTRACT FROM AUTHOR]

In this paper, simple modifications to the pseudospectral time-domain (PSTD) algorithm that offer dispersion compensation are presented. In a homogeneous lossless medium, the compensation offers an exact solution for one-dimensional (1D) propagation. For 2D and 3D propagation, the proposed method can compensate dispersion for a central frequency in any direction. The techniques are then extended to inhomogeneous materials containing piecewise constant electromagnetic properties and are shown to offer dispersion compensation. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 357–361, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20304 [ABSTRACT FROM AUTHOR]

This paper presents an improved subdomain multilevel approach (SMA), a technique efficiently used for solving large complex-shaped antennas printed in multilayered media structure. In a large electromagnetic problem, where the memory occupation and computational time have been already significantly reduced using the SMA, the calculation of the macro basis function (MBF) reaction terms remains the most time-consuming part of the procedure. In this paper, we present an efficient way of computing MBF reaction terms and reducing them to equivalent moments. The numerical results are compared with brute-force computations, the SMA, and the measurements. They demonstrate conclusively the efficiency and power of the new proposed technique. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 138–143, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20232 [ABSTRACT FROM AUTHOR]

In this paper, an efficient numerical simulation technique is introduced to extract the propagation characteristics of interconnects over lossy substrate structures. This approach is based on a compact-form FDFD method in conjunction with the two-step Lanczos (TSL) technique. The efficiency and accuracy of the algorithm are demonstrated through the simulation of several lossy transmission-line structures. [ABSTRACT FROM AUTHOR]

This paper presents the radiation patterns of the monopole antenna mounted on the rectangular shaped structure and the coupling problem between transmit (Tx) and receiver (Rx) antennas obtained by using the FDTD method. A comparison of FDTD calculated results with the exact solution for cylindrical structure validates the accuracy of the algorithm. Using the developed FDTD code, the power radiated from the Tx port influences the Rx port at the nearby working frequency of 2 GHz. The magnitude of coupling effects in terms of scattering parameters has the highest value of about -40 dB within the 2–3.5-GHz frequency range. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 265–268, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11348 [ABSTRACT FROM AUTHOR]

In this paper, a novel two-dimensional unconditionally stable finite-difference time-domain (2D US-FDTD) method based on the Crank–Nicolson (CN) scheme is proposed. In particular, in the proposed 2D US-FDTD method the field components are defined at only two time steps n and n + 1; and the original time-dependent Maxwell's equations of the Crank–Nicolson scheme are solved by introducing a proper intermediate value for a field component. Compared to the ADI-FDTD method, the US-FDTD method offers the following two advantages: (i) the left-hand and right-hand sides of the original updating equations are balanced (with regards to time steps) as accurately as possible and (ii) only a single iteration that requires fewer updating equations is needed for the field development. The numerical performance of the proposed US-FDTD method over the ADI-FDTD algorithm is demonstrated through numerical examples. In particular, it is shown that the asymmetric effect (that is, the asymmetric result is obtained even for exactly symmetric computational setups), which always appears in the ADI-FDTD algorithm, is not observed in the US-FDTD method. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 457–462, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11089 [ABSTRACT FROM AUTHOR]

This paper presents the design of a wideband corrugated multisectional conical horn using a genetic algorithm (GA). The GA optimizes the length, flare angle, and first slot depth of each section of the horn in order to match the admittance, reduce the voltage standing wave ratio (VSWR) of the horn, and generate the desired pattern. A VSWR of less than 1.6 is obtained over the frequency range 11–18 GHz. The optimized multisectional conical horn antenna has four sections, is less than 7λ long, and has very low sidelobe levels. The ratio between ratio between the co-polarization and the cross-polarization patterns is greater than 60 dB. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 352–356, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11058 [ABSTRACT FROM AUTHOR]

In this paper, an analysis of printed quadrifilar helical antennas (PQHAs) using the FDTD method is presented. We develop an in-house software taking into account the dielectric substrate. A tape form meshing is used in modeling the PQHA strip. A good agreement observed between theory and experimental results proves the validity of the method used by the in-house code for the PQHAs. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 172–175, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10712 [ABSTRACT FROM AUTHOR]

This paper presents a non-autonomous chaotic analysis of the Colpitts oscillator. It is available for injection-locked and synchronized designs of communication systems. The injected BJT Colpitts oscillator, constructed with Lur'e systems, is simulated and measured in applications. Using the Runge–Kutta algorithm, the phase portrait, time response, and power spectrum are represented with a series of simulation results. The dynamic maps of locking, transition, and normal areas are depicted by measurements of the related frequencies and output powers. Both simulation and measurement identify the amplitudes and frequencies of the injected sinusoidal wave, which affect the chaos in the Colpitts oscillator. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 175–181, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10713 [ABSTRACT FROM AUTHOR]

The error control of local interpolation for a 2D MLFMA will be discussed. The way to select proper parameters is proposed in terms of both numerical accuracy and computational cost. Satisfying the conditions derived in this paper, error can be controlled at the same level as global interpolation, and the computational cost becomes less expensive than the global one. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 8–12, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10655 [ABSTRACT FROM AUTHOR]

An improved conformal FDTD algorithm for microwave planar structure is presented in this paper. To achieve high-level accuracy and universality, but still keep the efficiency of the FDTD method, improved locally conformal algorithm and non-uniform orthogonal grids are employed to model the planar metal structures. All field components in destructed lattice are updated using locally conformal integral form of equations in order to achieve more accurate results. And with non-uniform orthogonal grids, arbitrary-shape metal strips can be modeled without generating a lot of unstructured meshes. In this algorithm, additional updating procedures for the fields in the destructed Yee lattice are no longer needed. The time marching procedures remain almost as simple as a uniform rectangular grids scheme. An oblique positioned microstrip stub structure is tested as an example to show the validity of this algorithm. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 219–224, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10562 [ABSTRACT FROM AUTHOR]

This paper presents an efficient solution for solving the generalized eigenvalue equation arising in the finite-element (FE) formulation of propagation characterization of planar transmission-line structures. A two-dimensional (2-D) finite-element method (FEM) is used for analyzing the uniform planar transmission lines. The Arnoldi algorithm is used in conjunction with the multifrontal decomposition of the system matrix for solving the eigensystem. Convergence is typically obtained within a few iterations of the Arnoldi process, and the formulation has proven to be robust, even when dealing with a significantly large number of unknowns. Numerical results are presented for the case of a uniform microstrip line, which clearly show the computational savings resulting from the use of the present approach. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 194–197, 2001. [ABSTRACT FROM AUTHOR]

In this paper, learning algorithms are used to decode QPSK data in a direct-conversion hardware (QPSK-unimode) microwave/millimeter-wave receiver using an application-specific six-port module. Two different algorithms, the K-means and Bayesian network, are considered for operation of the decoder to recover IQ data from QPSK modulated signals. Bit-error-rate (BER) results versus noise level (Eb/N0) are presented after a brief data-collecting period involving fewer than 500 data points. Results of the Bayesian network for Eb/N0=-3 dB and Eb/N0=-9 dB are presented, using the same data-gathering period. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 33–38, 2001. [ABSTRACT FROM AUTHOR]

In this paper, we study the transmission characteristics of an AOTF operating with ultra-short light pulses (2 ps). Initially, one considers the performance of the device, operating in the nonlinear regime without loss. It was observed that the effect of dispersion and nonlinearity has a strong influence on the pulse propagation when one increases the length of the AOTF. For a shorter length device, the switched pulse presents time broadening. For a higher length device, pulse break up was observed. Regarding the AOTF with loss, one considers a device of 0.25 mm length with a loss of 4 dB/mm constructed with an increasing nonlinearity profile. It was observe that the increase in β (increase of the final value of the profile Q(ξ) of the nonlinearity) changes the switched pulse from broadening to optical compression. One can say that the AOTF can be operated in a configuration that avoids pulse break up and has a switched pulse with a shorter time duration compared with the lossy AOTF. The study of the AOTF operating with ultra-short optical solitons provides possibilities for achieving high efficiency in ultra-fast all-optical signal processing, especially for optical switches, filters, and optical transistors. The acousto-optic tunable filter (AOTF) has attracted great attention in recent years, in part because it appears to be a suitable basis for multiwavelength optical cross connects. It is probably the only known tunable filter that is capable of selecting several wavelengths simultaneously. This capability can be used to construct a multiwavelength router. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 346–350, 2001. [ABSTRACT FROM AUTHOR]

In this paper, both the fast Fourier transform (FFT) and the preconditioned CG technique are first introduced into the method lines (MOL) to further enhance the computational efficiency of this semianalytic method. Electromagnetic wave scattering by an infinite-plane metallic grating is used as examples to describe its implementation. For an arbitrary incident wave, the Helmholtz equation and boundary condition are first transformed into new ones so that the impedance matrix elements are calculated by the FFT technique. As a result, this Topelitz impedance matrix only requires O(N) memory storage for the conjugate gradient FFT method to solve the current distribution involving the computational complexity O(N log N). The banded diagonal impedance matrix is selected as a preconditioner to speed up the convergence rate of the CG algorithm. Our numerical results show that the PCG–FFT method converges to an accurate solution in a much smaller CPU time. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 170–175, 2000. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive array algorithm is presented to minimize linear crosstalk in high-speed WDM systems. The algorithm is based on the optimum and the decision-directed algorithm added to the test signal sequences and sampling process. In transmitting data, the speed of algorithm processing reaches that of transmittance by a sampling process. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 100–102, 1999. [ABSTRACT FROM AUTHOR]

A neural network (NN)‐assisted probabilistic shaping (PS) distribution matcher is proposed, in which the model is simplified by a structured optimization method. The NN algorithm can encode the information sequence, making the signal obey the Gaussian distribution, and can directly restore the received signal. In addition, the algorithm uses the novel training method at both ends of the transmitter and receiver so that the system performance is significantly improved. PS system verification experiments have been carried out under 16QAM‐DMT modulation format. Under the hard decision forward error correction (FEC) threshold of 3.8*10−3 BER, the proposed system achieves 1.1 dB improvement compared to the traditional 16QAM‐DMT system. [ABSTRACT FROM AUTHOR]

A novel adaptive weighted geometric‐shaped (GS) 61 quadrature amplitude modulation (QAM) constellation is proposed in order to mitigate the nonlinear damage and increase the transmission distance. By introducing an adaptive weighting factor related to Kerr effect and fiber transmission distance in concentric regular hexagon constellation, the overlapping problem of the outer constellation points induced by nonlinear damage was reduced. The simulation results show that the proposed GS‐61QAM outperformed uniform 64QAM and has more obvious advantages in long‐haul optical transmission system. For a 120‐Gb/s coherent optical communication system, compared with uniform 64QAM, the proposed algorithm can obtain about 4.1 dB optical signal‐to‐noise (OSNR) gain at the BER of 10−2. Moreover, in order to further improve the system tolerance of nonlinearity, a scheme of adaptive weighted GS‐61QAM in coherent optical communication system utilizing K‐Means algorithm is proposed, the proposed scheme outperforms the traditional uniform 64QAM communication system by 5 dB in OSNR at the BER of 10−2. [ABSTRACT FROM AUTHOR]

This paper introduces a new effective finite-difference time-domain (FDTD) algorithm for modeling arbitrarily shaped dielectric surfaces. The new algorithm is based on an effective medium theory that makes the dielectric tensor effective. The proposed FDTD analysis of TE scattering by rotated two-dimensional (2-D) dielectric cylinders provides excellent numerical results. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 245–249, 1999. [ABSTRACT FROM AUTHOR]

In this paper, we design a central code controller for the FO–CDMA network. The central code controller assigns the lowest interference code set to users, and the code set is selected by the genetic algorithm. By this methodology, the code set can be found exactly, and the computing time is much faster than with the heuristic solution. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 27–30, 1999. [ABSTRACT FROM AUTHOR]

In this paper, a new family of pentagonal waveguides is proposed for high-power microwave transmission. Conformal mapping combined with the finite-difference method (CMFD) is used to analyze the propagation characteristics of the waveguides. The computed results agree well with the measurements. Finally, compared with other popular numerical methods, some distinguishing advantages of the CMFD are concluded. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 22: 420–423, 1999 [ABSTRACT FROM AUTHOR]

In this paper, the authors present a general subgridding scheme for enhancing the finite-difference time-domain (FDTD) algorithm. It is different from the conventional approaches in that it does not employ weighted averages of the electric or magnetic fields in the transition region from the coarse to the fine region, but instead employs a novel procedure for transferring the information between the two regions. We illustrate the application of the subgridding algorithm by considering a refinement factor of 5, and provide validation of the results obtained. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 330–333, 1999. [ABSTRACT FROM AUTHOR]

ABSTRACT In circular synthetic aperture radar (CSAR), targets are usually scanned over the complete azimuthal aperture of 360°. A major challenge inhibiting successful CSAR image production is encountered in two-dimensional imaging of relatively large scenes (i.e. wide-field scenarios). For such cases, the spatially variant radar signature gives rises to image degradations known as layover effects. In this paper, the imaging results for hypothetical and real complex targets using their CSAR data at C band are demonstrated to characterize these effects. In real experiments, a ground-based, outdoor CSAR system is exploited thanks to the circular balcony of a building that provides 270° view of targets. A spherical back-projection algorithm is used to focus near-field data and the reconstructed images are also cleaned out from clutter to more easily visualize the layover artifacts. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:489-497, 2015 [ABSTRACT FROM AUTHOR]

The in-band sidelobe levels of a moving phase center antenna array can be significantly lowered by applying a static excitation amplitude distribution, which is more economical and convenient to implement than those employing dynamic excitation distribution. This paper describes a differential evolution algorithm method for determining the static excitations, via application to a 40-element linear array. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 83–85, 2003 [ABSTRACT FROM AUTHOR]