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In most of the existing ground penetrating radar (GPR) imaging algorithms, using either full or sparse data collection, the ground is modeled as a single half-space layer. In this paper, a generalized sparse imaging approach with total variation minimization (TVM) for multiple-input multiple-output (MIMO) GPR imaging through multilayered subsurface is proposed. The multilayered media Green’s function is incorporated in the imaging algorithm to take into account the complex wave propagation effects under multilayered subsurface. An analytical expression of the layered subsurface Green’s function is derived using the stationary-phase method, which significantly reduces the computation time and complexity. On the other hand, as TVM minimizes the gradient of the image, its incorporation in the imaging algorithm results in a reconstruction that preserves the geometry and edges of the targets better than the standard L1-minimization-based sparsity-driven imaging. The number of antenna elements and frequency measurements in MIMO GPR system can be significantly reduced using the proposed technique without degradation of the image quality. Although MIMO configuration is investigated in this paper, the presented approach can be simply applied to monostatic synthetic aperture radar. [ABSTRACT FROM AUTHOR]

Different variations of the covariance matrix adaptation evolution strategy (CMA-ES) are used in the design and optimization of electromagnetic (EM) problems. Two different schemes for the implementation of mixed-parameter CMA-ES and one scheme for the implementation of multiobjective CMA-ES are presented. Mixed-parameter CMA-ES is attractive in EM optimization when both continuous and discrete design parameters are involved. The first mixed-parameter scheme uses a Poisson mutation operator to update the discrete variables, and the second one forces an integer mutation on discrete variables with small variances. Multiobjective CMA-ES, developed in this paper, optimizes designs with respect to multiple objective functions simultaneously. It ranks the candidate solutions according to two levels: nondominated sorting and crowding distance. Several antenna and microwave design problems are presented to evaluate the performance of these schemes and compare them with other nature-based optimization algorithms. [ABSTRACT FROM PUBLISHER]

Most of existing through-the-wall radar imaging (TWRI) algorithms deal with a single layer homogeneous wall in two-dimensional scenario. In this communication we present a generalized three-dimensional (3-D) beamforming algorithm for the focused imaging of targets behind multilayered building walls. The far field layered medium Green's function is incorporated in the 3-D beamformer for the compensation of the wall effect. 3-D polarimetric imaging is exploited in TWRI for enhanced target identification and feature extraction as well as wall effect mitigation. Numerical results show that the proposed 3-D beamformer provides high quality focused images in various wall-target scenarios. [ABSTRACT FROM AUTHOR]

In this paper, a 3-D diffraction tomographic algorithm is proposed for real-time through-the-wall radar imaging (TWRI). The spectral expansion of the three-layered medium dyadic Green's function is employed to derive a linear relationship between the spatial Fourier transforms of the image and the scattered field under Born approximation. Then, the image can be efficiently reconstructed with inverse fast Fourier transform (IFFT). The linearization of the inversion scheme and the easy implementation of the algorithm with FFT/IFFT make the diffraction tomographic TWRI algorithm suitable for on-site applications. The 3-D polarimetric TWRI is investigated using the proposed algorithm for the enhanced target detection and feature extraction as well as mitigation of the wall effect in the cross-polarization. Numerical and experimental results are presented to show the effectiveness and high efficiency of the proposed algorithm for 3-D real-time TWRI. [ABSTRACT FROM AUTHOR]

Following our previous work, here an artificial magnetic conducting (AMC) surface, comprised of Hilbert and/or Peano space-filling curve inclusions is utilized as a thin electromagnetic absorber. Numerical results are presented to show the effects of the incident angle, conducting strip widths and substrate thicknesses on the absorbing properties of such surfaces. The performance of a fabricated thin absorber in reducing the RCS of a conducting plate is demonstrated through measurement. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 785–790, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24186 [ABSTRACT FROM AUTHOR]

In this paper, we review recent advances in evolutionary programming (EP) and its implementation in various antenna, microwave, frequency selective surfaces and RF circuit optimization problems. EP, unlike the other two paradigms of evolutionary computational techniques, namely, genetic algorithms (GA) and evolution strategies (ES), uses a mutation only variation operator where adaptive and/or self-adaptive techniques exist, or can easily be designed, for adapting the parameters of mutation operator during the evolution process. We present the so-called meta-EP and design of its mutation operator, using Gaussian, Cauchy and Poisson mutations as well as a hybrid of these mutations, for continuous, discrete and mixed parameter electromagnetic optimization problems. In addition, an efficient hybrid use of EP, gradient search methods and cluster analysis, as well as a novel hybrid EP-GA algorithm are discussed. Examples presented include optimizations of corrugated horn antennas, multilayered stacked microstrip antennas, Yagi-Uda arrays, partially reflective surfaces, dielectric filters, meander-line polarizer and RF duplexers [ABSTRACT FROM PUBLISHER]

An evolutionary programming algorithm with a mixed continuous-discrete parameter representation for application in electromagnetic optimization problems is presented. In our approach, the mutation operator consists of a hybrid combination of Gaussian mutation for the continuous parameters, and Poisson mutation for the discrete parameters. The implementation uses self-adaptive schemes for updating the standard deviation of the Gaussian distribution and the mean of the Poisson distribution during the evolution. As an example, the proposed evolutionary algorithm is applied to the constraint designs of various multilayer dielectric-filter structures. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 267–271, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11187 [ABSTRACT FROM AUTHOR]

Closed form expressions for the Green's functions of a planar microstrip structure on an electrically thin uniaxially anisotropic substrate have been derived. The approach is to first obtain the quasi-dynamic term and refine its accuracy with a correction term valid for higher frequencies. The quasi-dynamic term conveys the influence of partial images and includes both transverse and vertical dielectric constants ℇrt and ℇrz. The correction term, on the other hand, results in an expression that includes ℇrz only. Results indicate excellent agreement with exact numerical solution over a significant band of frequencies and over a large range of spatial values. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 161–168, 2003. [ABSTRACT FROM AUTHOR]

A set of closed-form Green's functions is used in a mixed-potential integral-equation technique for the efficient modeling of planar microstrip structures of arbitrary shape on an electrically thin substrate. Various MMIC and microstrip antenna structures are simulated. It is shown that excellent accuracy at a substantial reduction in total simulation time is achieved for a wide range of frequencies and substrate parameters. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 20: 342–345, 1999. [ABSTRACT FROM AUTHOR]

The feasibility of obtaining high gain from a class of “Yagi-like” multilayer printed stacked dipole arrays is investigated. A moment-method approach is used to numerically model the array structure. Numerical results for the case of a three-layer stacked microstrip Yagi are presented. It is shown that the use of Yagi-like parasitic director elements can result in a gain of 10 dBi or higher without the need for a high-permittivity superstrate layer. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 317–321, 1998. [ABSTRACT FROM AUTHOR]

By invoking a thin substrate approximation, accurate spatial-domain expressions for the Green's functions, Ge and Gm, of microstrip structures in a magneto-dielectric substrate are derived. The expression for Gm is given in terms of a quasidynamic solution corresponding to a point source and Its partial images, while that of Go is derived in terms of a quasidynamic contribution plus a correction term. It is demonstrated that the addition of the correction teem is needed in order to accurately calculate Ge in the near field. [ABSTRACT FROM AUTHOR]

The fundamental radiation characteristics of a microstrip antenna on a cylindrical substrate with a thick cover layer is investigated by using a magnetic line source model. Numerical results for the radiation pattern and conductance are presented. It is found that certain combinations of curvature radius and cover-layer thickness could result in significant distortions in the pattern. Lossy dielectric material may be used to reduce these undesired effects. [ABSTRACT FROM AUTHOR]

We consider a dual-function radar communication (DFRC) system employing frequency hopping (FH) radar waveforms. Each communication symbol is represented by a phase-modulated pulse sequence that multiplies the radar hops in fast-time and transmitted from a multiple-input multiple-output radar platform. In this respect, the DFRC system considered follows the code-shift keying (CSK) signal embedding strategy. The phase modulations include phase-shift keying (PSK), derivative PSK, and continuous phase modulation. The CSK pulse sequences and the FH code are jointly designed to reduce range sidelobe levels (RSLs) and combat range sidelobes modulation. It is shown that the joint optimization using the genetic algorithm yields desired CSK sequences and FH code matrix with less computational complexity compared to the exhaustive search algorithm. The power spectral density and detection performance of various DFRC systems are analyzed, underscoring the tradeoff between RSLs and spectral sidelobe levels. The proposed DFRC system with optimum phase sequences and hopping code achieves high data communication rates by permitting frequencies to be reused in the radar hops. [ABSTRACT FROM AUTHOR]

Investigates the radiation performance of rectangular microstrip patch antennas on two ceramic substrates, barium-titanate and neodymium-titanate. Radiation patterns; Effect of reducing the ground plane size on radiation patterns, cross-pol levels and resonant frequency of the patch antennas.

• PhaseCut needs a high CPU cost, which limits its use in high resolutionpatterns. • The proposed method is aimed at the retrieval of high-resolution phase pattern. • The proposed method is based on a hybrid of PhaseCut and alternating projection. • Simulation shows that the method can quickly get the near-global solution. Phase retrieval is an important research topic in the optics field. It is aimed to reconstruct the wave-front from the intensity of the far-field diffracted field. To deal with the local stagnation of conventional iterative Fourier-based algorithms, an interesting recent approach formulates the phase retrieval problem as a tractable relaxation (called PhaseCut). Despite its powerful global capability, the operation of recasting a vector problem into a matrix problem leads to higher computational cost, which limits its use in far-field patterns with high resolution. In this paper, we develop an extrapolative alternating projection algorithm to cope with the reconstruction of high-resolution phase pattern. The algorithm starts with a low-resolution phase estimation solved by PhaseCut from the far-field amplitudes in the low frequency range, and then refines the initial estimation by an extrapolative iterative projection method, which has a low computational complexity. The iterative process is divided into various periods where the inputs of the algorithm (far-field amplitudes) are extrapolated to include more high frequency information. The main contribution is that the algorithm can quickly converge to the globally optimal and high-resolution solution with a high probability. We verified the validity of the algorithm with various numerical simulations. [ABSTRACT FROM AUTHOR]

We propose in this work a dynamic group sparsity (DGS) based time-frequency feature extraction method for dynamic hand gesture recognition (HGR) using millimeter-wave radar sensors. Micro-Doppler signatures of hand gestures show both sparse and structured characteristics in time-frequency domain, but previous study only focus on sparsity. We firstly introduce the structured prior when modeling the micro-Doppler signatures in this work to further enhance the features of hand gestures. The time-frequency distributions of dynamic hand gestures are first modeled using a dynamic group sparse model. A DGS-Subspace Pursuit (DGS-SP) algorithm is then utilized to extract the corresponding features. Finally, the support vector machine (SVM) classifier is employed to realize the dynamic HGR based on the extracted group sparse micro-Doppler features. The experiment shows that the proposed method achieved 3.3% recognition accuracy improvement over the sparsity-based method and has a better recognition accuracy than CNN based method in small dataset. [ABSTRACT FROM AUTHOR]

ABSTRACT A novel configuration of a compact stair-like ultrawideband (UWB) planar monopole antenna is presented for improved boresight gain performance and pattern stability. The geometry of the basic antenna has been modified to include a gate-like ground plane structure which alleviates unwanted squinting effects in the gain pattern at higher frequencies. The boresight gain is then further enhanced through the addition of a stacked parasitic patch composed of a scaled copy of the basic stair-like geometry. Prototypes of the proposed antenna geometries are fabricated and measured to validate the concept. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2809-2812, 2014 [ABSTRACT FROM AUTHOR]

In this paper, we describe and utilize polarization contrast techniques of the adaptive polarization difference imaging algorithm and its transient modification for through-wall microwave imaging (TWMI) applications. Originally developed for optical imaging and sensing of polarization information in nature, this algorithm is modified to serve for target detection purposes in a through-wall environment. The proposed techniques exploit the polarization statistics of the observed scene for the detection and identification of changes within the scene and are not only capable of mitigating and substantially removing the wall effects but also useful in detecting motion, when conventional Doppler techniques are not applicable. Applications of the techniques to several TWMI scenarios including both homogeneous and periodic wall cases are presented. [ABSTRACT FROM AUTHOR]

This article presents a novel, low-cost, beam-switchable 2 x 10 antenna array system operating at 60 GHz. This antenna system is constructed of two rows of Chebyshev-tapered microstrip antenna arrays. Each row is a 10 element series-fed array which are fed by a 90° coupler. The designed antenna array has only two input ports, but it is capable of generating three switchable beams. This antenna system can spatially scan 90° with at least -5 dB normalised gain using only one SPDT switch and a single transceiver. The maximum gain realised by the system was measured as 16.4 dBi and the bandwidth (BW) was >1 GHz. The features of the proposed antenna system make it applicable to do mmWave research such as beamforming algorithms and channel sounding, and to use in handsets for 5G communication. [ABSTRACT FROM AUTHOR]

This article deals with a study of novel classes of metamaterial inclusions based on space-filling curves. The graph–theoretic Hamiltonian-path (HP) concept is exploited to construct a fairly broad class of space-filling curve geometries that include as special cases the well-known Hilbert an Peano curves whose application to metamaterial inclusions has recently been proposed. In this framework, the basic properties of HP are briefly reviewed, and a full-wave study of the electromagnetic properties of representative grid-graph HP geometries is carried out. Applications to metamaterial inclusions are explored, with focus on artificial magnetic conductors with reduced polarization-sensitivity. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48:2520–2524, 2006; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.21982 [ABSTRACT FROM AUTHOR]