This paper mainly deals with the problem of target detection in compound-Gaussian clutter with orthogonal frequency division multiplexing (OFDM) radar. First, the OFDM measurement model is developed to compound-Gaussian clutter by taking advantage of frequency diversity of OFDM radar waveform and we devise a generalized likelihood rate test (GLRT) detector where the target scattering coefficients and clutter covariance matrix are unknown. Then, we propose an adaptive waveform design scheme based on maximizing Mahalanobis distance of the distributions under two hypothesises to improve the detection performance. Finally, the effectiveness of the proposed detector as well as the adaptive waveform design method is demonstrated via numerical examples.

In this paper, a CPW-fed reconfigurable clover-shaped antenna with switchable circular polarization is proposed. This antenna consists of a clover-shaped patch, four p-i-n diodes, and two pairs of quarter-circular-rings. By electrically controlling the four p-i-n diodes to form two orthogonal bow-tie shaped current paths, the proposed antenna can be operated in two modes: the left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) modes. Two pairs of quarter rings are used to improve the bandwidth and AR performance of the antenna. The measured 10-dB reflection coefficient and 3-dB axial-ratio (AR) bandwidth of the prototype antenna is approximately 12.3% and 19%, respectively, which is enough for some wireless applications such as WLAN IEEE 802.11 b/g (4%). Gain and radiation pattern are also presented.

A compact circularly polarized (CP) crossed dipole antenna with chip inductors and square rings loaded for Global Positioning System (GPS) is proposed in this letter. The CP radiation is produced by crossing two dipoles through a 90° phase delay line of a vacant-quarter printed ring. Four chip inductors inserted in the dipole arms and four square rings loaded at the back of the dipole arms are introduced to obtain a compact dipole size. The plane dimension of the proposed antenna is 28 mm×28 mm, which can be widely used for GPS handheld devices. Details of the proposed antenna design and results are presented and discussed.

The PMCHWT-IE-FFT-BURA is applied to the wideband analysis of electromagnetic scattering property of homogeneous targets. Over the broad frequency band, the fast computation is achieved by the Maehly expansion on the basis of the Chebyshev approximation of the electric and magnetic currents. On the Chebyshev sampling points, PMCHWT-IE-FFT greatly reduces the memory requirement by sparsely storing the impedance matrix and decreases the computational time to the greatest degree by block acceleration of the matrix-vector product. Finally, numerical results show that the proposed method can make efficient analysis of wideband property of homogeneous targets without sacrificing accuracy much.

The generalized Fibonacci multiferroic superlattices (GFMS) are composed of single-phase multiferroic domains with simultaneous polarization and magnetization and are defined by the binary substitutional rule (B → B^mA, A → B, m = 2, 3). We propose to construct a nonreciprocal multi-channel bandstop filter by the GFMS. The couplings between electromagnetic waves and lattice vibration of multiferroic material with ferroelectric and ferromagnetic (or antiferromagnetic) orders can be invoked either through piezoelectric or piezomagnetic effects and can lead to the creation of the polaritonic band structure. The plane wave expansion method with first-order approximation predicts the existence of multiple band gaps, and electromagnetic waves lying within the band gaps are prohibited, and the band gaps with respect to forward electromagnetic waves (FEWs) and backward electromagnetic waves (BEWs) are asymmetric. The forbidden band structures with FEWs and BEWs are calculated by the transfer matrix method and multiple frequency channels with unidirectional transmission of electromagnetic waves can be further confirmed. Nine and twenty transmission dips in transmission spectra for the BEWs in the frequency range of ω = 0.4 − 0.6 (17.06 GHz-25.59 GHz) are found in the GFMS with m = 2 and 3, respectively, in which the BEWs are prohibited while the FEWs can travel. Thus, the GFMS has all the conditions for the nonreciprocal multi-channel bandstop filter. Besides, the GFMS can also be applied to construct compact multi-channel one-way electromagnetic waveguides.

In this paper, the mathematical analysis of a single-walled carbon nanotube composite material (SWCNT-composite) is presented in order to estimate its effective conductivity model and other important parameters. This composite material consists of SWCNT coated by other different materials. The effects of the radius of SWCNT and average thickness of coating layer on this effective conductivity model are investigated. The effects of using different types of coating materials with different radii of SWCNTs on the behavior of this composite material are also presented. An investigation of electromagnetic properties of SWCNT-composite material was carried out based on designing and implementing the dipole antenna configuration using a common electromagnetic engineering tool solver CST (MWS). The results obtained from comparisons between SWCNT and SWCNT-composite materials are presented based on their electromagnetic properties are also described in this paper.

In this paper we analyze the 3D modes of a linear homogeneous magnetoelectroelastic (MEE) material reduced to magnetoelectric (ME) constitutive form. This allows convenient examination of the predominately electromagnetic behavior in a mechanically coupled MEE material system. We find that the behavior of the electromagnetic modes are strongly in fluenced by the mechanical coupling present in the MEE material system. A number of papers refer to the cross-coupling of laminated piezoelectric and piezomagnetic materials as magnetoelectric materials. We discuss here that the composite materials are MEE systems and that the constitutive relations need to reflect the mechanical coupling also. Further, we find that the mechanical coupling has a significant impact on the electromagnetic propagation modes of the composite material. Through examples of homogenized MEE materials we show possibilities for remarkable electromagnetic material characteristics which are not conventionally obtainable in single phase materials.

Doppler weather radar is an effective tool for monitoring mesoscale and small scale weather systems, quantitatively estimating precipitation and guarding against severe convective weather. The quality of the data obtained by Doppler weather radar will be seriously affected by the anomalous propagation of electromagnetic wave in tropospheric ducts. A novel method is introduced in this paper to retrieve the surface ducts, and it is based on the Principal Component Analysis (PCA) method for modeling M profile and Parabolic Equation (PE) propagation model which is a well-established technique for efficiently solving the equations for beam propagation in an inhomogeneous atmosphere. The inversion echo powers and equivalent reflectivity factor are in accordance with the measured data, which indicates that the surface ducts can be effectively retrieved by this method.

The optical theorem is a fundamental result that describes the energy budget of wave scattering phenomena. Most past formulations have been derived in the frequency domain and thus apply only to linear time-invariant (LTI) scatterers and background media. In this paper we develop a new theory of the electromagnetic form of the optical theorem directly in the time domain. The derived formulation covers not only the ordinary optical theorem but also the most general form of this result, known as the generalized optical theorem. The developed formulation provides a very general description of the optical theorem for arbitrary probing fields and general scatterers that can be electromagnetically nonlinear, time-varying, and lossy. In the derived formalism, both the scatterer and the background medium can be nonhomogeneous and anisotropic, but the background is assumed to be LTI and lossless. The derived results are illustrated with a computer simulation study of scattering in the presence of a corner reflector which acts as the background. Connections to prior work on the time-domain optical theorem under plane wave excitation in free space are also discussed.

In this paper, a novel circularly-polarized (CP) patch antenna using organic magnetic substrate is proposed. This patch antenna works at 1.575 GHz frequency band which is for the global positioning system (GPS) application. The organic magnetic material is used to realize the miniaturization of antenna. To improve gain and axial ratio bandwidth of the antenna, fractal Hi-impedance surface electro-magnetic band gap (EBG) structures was used. The proposed antenna has been fabricated and measured. The simulation results for operating frequency band are shown to have good agreement with measurements.

The paper presents a hybrid evolutionary algorithm suitable for the optimization of large-domain electromagnetic problems. The hybrid technique, called Genetical Swarm Optimization (GSO), combines Genetic Algorithms (GA) and Particle Swarm Optimization (PSO). GSO algorithm is modelled on the concepts of Darwin's theory based on natural selection and evolution, and on cultural and social rules derived from the swarm intelligence. The problem is formulated and solved by means of the proposed algorithm. The examples are simulated to demonstrate the effectiveness and design flexibility of GSO in the framework of synthesis of multi-beam linear antennas arrays.

This paper addresses the miniaturization of Quadrifilar Helix Antennas (QHAs) for space applications (VHF Telemetry, Tracking and Command). Several shape miniaturization techniques were presented, and the impact of height reduction is quantified in terms of radiation pattern, gain and phase center. Simulated and experimental results demonstrate that Compact Quadrifilar Helix Antennas (CQHAs) with a height reduced up to 70% reported to the reference QHA can be designed. By using an appropriate optimization method, the impact of the miniaturization on CQHA performances in terms of radiation pattern and polarization purity can be minimized. Moreover, the impact on the gain is quantified, and design rules are reported. Finally a closed-form expression for estimating the gain of CQHAs from the height reduction factor is found.

Left-handed metamaterial (LHM) lenses allow the focusing of microwave radiation at specific positions within a medium, depending on its refractive index. A suitable approach needs to consider the reflections between the LHM lens and the adjacent media. This work faces the challenge of focusing the microwave radiation within a medium with arbitrary positive refractive index and characteristic impedance using LHM lenses as imaging-forming systems. To find a right lens formula, a full wave method is presented in theory. The results we achieved show that the characteristic flat shape of conformal-four lens configuration has a spot size of 0.53 x 0.34λ_eff² at -3 dB if the different media are perfectly matched. Otherwise, a noteworthy aberration affects the focusing, but it can be mitigated using a conformal circular LHM lens with a spot size of ~0.4 x 0.4λ_eff² at -3 dB.

While considerable progress has been made in the realm of speed-enhanced electromagnetic (EM) solvers, these fast solvers generally achieve their results through methods that introduce additional error components by way of geometric type approximations, sparse-matrix type approximations, multilevel type decomposition of interactions, and assumptions regarding the stochastic nature of EM problems. This work introduces the O(N logN) Unied-FFT grid totalizing (UFFT-GT) method, a derivative of method of moments (MoM), which achieves fast analysis with minimal to zero reduction in accuracy relative to direct MoM solution. The method uniquely combines FFT-enhanced Matrix Fill Operations (MFO) that are calculated to machine precision with FFT-enhanced Matrix Solve Operations (MSO) that are also calculated to machine precision, for an expedient solution that does not compromise accuracy.

In this paper, we investigate the diffraction of complex structures applying a new hybridization between generalized PO (Physical Optic) and MoM-GEC method. The proposed approach is developed to speed up convergence, alleviate calculation and then provide a considerable gain in requirements (processing time and memory storage) because it is based on a single test function instead of numerous sinusoidal or polynomial ones. Based on this approach, each metallic pattern is modeled by a current trial function that consists of two parts. The first part is called modal current, and it is decomposed on Hankel functions for modeling metal edges. However, the second part concerns the middle of metallic patterns, and it is modeled by PO method and called generalized PO current. Based on this approach, we study the diffraction of unidimensional structures, then we generalize our approach to take bidimensional ones. For validation purpose, we investigate 1D and 2D reflectarrays to prove the new approach's benefits. The obtained results show good accuracy with the method of moments. Moreover, we prove the considerable improvements in CPU time and memory storage achieved by the hybrid approach when studying these structures.

The open rectangular grating with step-loaded slow-wave structure (SWS), a type of all-metal SWS for high power wide band mm-wave wave traveling wave tubes (TWT) is presented in this paper. By using the jumping conditions at the interface of two neighboring steps and single-mode approximation (SMA) field matching theory, the dispersion equation and coupling impedance of this SWS were obtained. Then the obtained complex dispersion equation was numerically calculated, and the slow-wave characteristics of the fundamental wave of this structure were discussed. Moreover, the calculation results by our theory were accordant with the simulation data obtained by the 3-D electromagnetic simulation software HFSS, The numerical calculation results show that the dispersion characteristics and coupling impedance are notably improved by loading the steps. And the working bandwidth may be the widest when the thickness of the step is about equal to the thickness of the groove depth. The proper design parameters can be optimized to meet the needs of high frequency characteristics with wide bandwidth and high output power. The present study will be useful for further research and design of this kind of high frequency system.

This paper presents a novel and robust design for a new kind of photonic crystal fiber with dodecagonal and circular array of air holes, aiming at a highly nonlinear coefficient, ultra-flattened dispersion and ultra-low confinement loss. In this structure, circular lattices are added in two inner layers to obtain both ultra-low dispersion and ultra-flattened dispersion in a wide wavelength range. The proposed structure has a modest number of design parameters for easier fabrication. The finite difference method with perfectly matched boundary layer is used to analyze guiding properties. Analysis results prove that the proposed highly nonlinear dodecagonal photonic crystal fiber obtains a nonlinear coefficient greater than 43 (W.Km)^-1 and low dispersion slope 0.003 ps/(nm.km) at 1.55 μm wavelength. Ultra-flattened dispersion of 0.8 ps/(km.nm) is also obtained ranging from wavelength 1.3 μm to 1.7 μm with confinement loss lower than 0.5×10^-6 dB/m in the same wavelength range.

A fast finite difference delay modeling (FDDM)-based scheme is presented for analyzing transient electromagnetic scattering from lossy inhomogeneous dielectric objects. The proposed scheme is formulated in the region of the scatterers by expressing the total field as the sum of the incident field and the radiated field due to both the polarization and conduction current density. The current density is discretized in space by Schaubert-Wilton-Glisson basis functions and in time by finite differences. Furthermore, the scheme is accelerated by the fast Fourier transform (FFT) algorithm, which can reduce the memory requirement and computational complexity significantly. Numerical results are presented to illustrate the accuracy and efficiency of the proposed method.

The reflectivity measurement of materials is an innovative application of a reverberation chamber (RC). In this paper we show an analysis of the performance of the reflectivity measurement in an RC in terms of uncertainty of measurement and relevant noise level. The model for reflectivity measurement, which is already present in literature, is based on the absorption cross section (ACS) measurements. If the ACS measurements are averaged with respect to the configurations of the measurement system, then the relevant uncertainty depends only on the number of independent samples. Here, the performance of the reflectivity measurements is shown in cases where it depends only on the number of independent samples acquired in an RC. Simulations and measurements confirm the validity of the expected results.

A three-dimensional (3D) time domain approach can be particularly valuable for the analysis of many different types of practical structures. In this regard, the finite difference time domain (FDTD) method is a popular technique, being used successfully to analyze the electromagnetic properties of many structures, including a range of optical or photonic devices. This FDTD method offers several major advantages: a minimum level of calculation is required for each of the cells into which the structure is divided, as well as data parallelism and explicit and easy implementation: however, the use of a cuboid grid makes the method very resource intensive for large simulations, especially those in 3D. Although the finite element (FE) approach is superior for the discretization of two-dimensional (2D) and 3D structures, most of the FE-based time domain approaches reported so far suffer from limitations due to the implicit or iterative form or the mass matrix formulation, for example. This paper presents an FE based time domain technique for 3D structures which uses a unique perforated mesh system. It calculated the numerical dispersion characteristics for the FDTD and the proposed method and compared. This paper finally discusses how to utilize the improved numerical dispersion characteristics of the proposed method to increase the simulation speed beyond the FDTD 3D method by using Intel micro-processors.