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.

The paper introduces a new class of adaptive CFAR methods to cope with the problem of outliers due to the presence of clutter edges and interfering targets. A fundamental distinction between the proposed approach and existing adaptive CFAR approaches is that in order to maintain robust performance the former uses information on positions at which estimated outlier-free cells appear in the full reference window and the statistics of the sample in the cell under test. The performance of one of the possible implementations of new adaptive CFAR methods is studied and compared with that of an existing adaptive CFAR approach. The results show significant advantages of the proposed class of adaptive CFAR methods in both the false alarm regulation property and detection performance.

Two major performance degrading factors in free space optical communication systems are rainfall and atmospheric turbulence. We study the outage probability and bit-error rate for free-space communication links with spatial diversity and Gaussian-Schell electromagnetism beams over the raining turbulence fading channels by double inverse Gaussian distribution proposed in this paper. Assuming intensity-modulation/direct detection with on-off keying and perfect channel state information, we derive expressions of average bit-error rate and outage probability of multiple-input multiple output free space optical communication systems over double inverse Gaussian model. The effects of scintillation index of raining turbulence, spatially coherence of source, pointing errors and spectral index of non-Kolmogorov turbulence on the outage probability and bit-error rate of multiple-input multiple-output free space optical communication systems are examined.

In this paper, a printed planar monopole antenna (PPMA) is presented for PCS, UWB and X-band. The antenna is designed in two stages. In the design of the preliminary PPMA used to obtain the proposed PPMA, the structure is divided into sections, and they are optimized in the sense of bottom to up strategy. The bandwidth is enhanced by employing tapered transitions and inset feed. The resulting antenna operates between 2.37 GHz and 12 GHz with VSWR<2 and an average peak realized gain (G_pr) of 4.95 dB. Therefore, the preliminary antenna can be considered to be suitable for Bluetooth, WLAN, WiMAX, UWB and X-band. The proposed PPMA is designed by implementing slots on the preliminary PPMA to include PCS, and to suppress Bluetooth and commonly used WLAN and WiMAX bands, the ones allocated out of UWB. The proposed antenna operates in the 1.67 GHz-1.91 GHz and 3 GHz-15 GHz bands with VSWR<2. The G_pr in PCS is 1.32 dB at 1.8 GHz, and the average G_pr is 5 dB for the 3 GHz-15 GHz band. The group delay performances are also examined, and the maximum group delay deviations of preliminary and proposed PPMAs are observed as 1 ns and 1.25 ns, respectively.

A novel planar ultra-wideband (UWB) antenna with triple-notched bands is investigated and presented in this paper. The initial UWB antenna consists of a circular-shaped radiating element, a 50 Ω microstrip feed line, and a partially truncated ground plane. Then, by embedding a square ring short stub loaded resonator (SRSSLR) beside the microstrip feedline of the basic UWB antenna, band-rejected filtering properties in the satellite communication/wireless local area network/radio frequency identification for microwave access bands are generated. The notched frequencies can be adjusted according to specification by changing the SRSSLR. The results indicate that the proposed compact antenna not only retains an ultra wide bandwidth, but also owns triple band-rejections capability. The UWB antenna demonstrates omnidirectional radiation patterns across nearly the whole operating bandwidth that is suitable for UWB communications.

This paper deals with a fast and simple computational method of 3D near-field (NF) radiation from 2D planar frequency- and time-dependent data. The established calculation method can be used to predict the electromagnetic (EM) emission from various types of electronic devices. The proposed method is originally applicable to the computation of the EM NF along the arbitrary shaped curvilinear 3D surface of multi-shape objects. The EM computation consists in the application of the planar NF-to-NF transform using plane wave spectrum. The relevance of the established method is verified with three different validation tests of analytical and practical demonstrations. The first validation is based on the analytical NF radiation from set of elementary dipoles excited by a harmonic signal. The second validation test is based on the experimented data from a hybrid active printed circuit boards (PCBs) in the frequency domain. The last validation test is performed with the measured NF data from a microstrip planar circuit in the time-domain. For all the different test cases, the plots of EM NF on arbitrary curvilinear surfaces are presented. Applications with 3D visualization or holographic surface with arbitrary geometry of EM radiation from planar data in both frequency- and time-domains confirm the effectiveness of the proposed method to predict the EM NF emission from complex PCBs. The developed 2D-to-3D computational method is particularly useful for radiated EM compatibility engineering.

In this paper, a nonlinear phase enhancement of multi-resonance composite right/left-handed unit cell for multi-band antennas is presented. Different antennas with nonlinear enhanced phase which can operate up to five different frequency bands are introduced. Meanwhile, the proposed antennas have compact size so that they can demonstrate size reduction up to 60% compared to conventional patch antennas operating at the same frequencies. The achieved phase enhancement has been validated by comparing two different configurations of composite right/left-handed cells. The analysis, electromagnetic full wave simulations and experimental results are discussed. A reasonable agreement is achieved between the measured and simulated results.

A new microstrip ultra-wideband (UWB) bandpass filter (BPF) with triple-notched bands is presented in this paper. The circuit topology and its corresponding electrical parameters of the basic microstrip UWB BPF are designed by modified genetic algorithm (MGA). Then, triple-notched bands inside the UWB passband are implemented by coupling a novel triple-mode stepped impedance resonator (SIR) to the main transmission line of the basic microstrip UWB BPF. The triple-notched bands can be easily generated and set at any desired frequencies by varying the designed parameters of triple-mode SIR. For verification, a new microstrip UWB BPF with triple-notched bands respectively centered at frequencies of 4.4 GHz, 5.9 GHz and 8.0 GHz is designed and fabricated. Both simulated and experimental results are provided with good agreement.

A simple 2×3 reconfigurable beam-forming network (R-BFN) for four-beam reconfiguration application is designed and implemented. The proposed R-BFN with two input ports and three output ports consists of a 2:1 power divider, a 90° hybrid, a 180° hybrid and a 2-bit phase shifter. The 2-bit phase shifter has two states: one is a 180° phase shifter (State 1); the other is a 0°/360° phase shifter (State 2). By introducing the 2-bit phase shifter, the constant phase differences of three output ports can be reconfigured. Specifically, as different input ports are excited, the R-BFN provides three output signals with equal power levels and the progressive phases of -120° and 120° when the 2-bit phase shifter at state 1, while -60° and 60° when the 2-bit phase shifter at state 2, respectively. When the proposed R-BFN is connected to an antenna array, a four-beam reconfiguration is obtained. Simulated and measured results show that good impedance matching, high port isolation, equal power division, and constant phase difference have been achieved simultaneously within the operation band of 2.4-2.6 GHz. The capability of the proposed R-BFN to reconfigure beams is also verified experimentally by using a 2.5 GHz dipole array.