High-order unconditionally-stable three-dimensional (3-D) four-step alternating direction implicit finite-difference time-domain (ADI-FDTD) methods are presented. Based on the exponential evolution operator (EEO), the Maxwell's equations in a matrix form can be split into four sub-procedures. Accordingly, the time step is divided into four sub-steps. In addition, high-order central finite-difference operators based on the Taylor central finite-difference method are used to approximate the spatial differential operators first, and then the uniform formulation of the proposed high-order schemes is generalized. Subsequently, the analysis shows that all the proposed high-order methods are unconditionally stable. The generalized form of the dispersion relations of the proposed high-order methods is carried out. Finally, in order to demonstrate the validity of the proposed methods, numerical experiments are presented. Furthermore, the effects of the order of schemes, the propagation angle, the time step, and the mesh size on the dispersion are illustrated through numerical results. Specifically, the normalized numerical phase velocity error (NNPVE) and the maximum NNPVE of the proposed schemes are lower than that of the traditional ADI-FDTD method.

This paper presents a novel design of dual-linear-polarized broadband horn antenna for 6~18 GHz frequency band. Applying commercial software Ansoft HFSS, parametric analysis is taken with respect to the best antenna performance and manufacturing tolerance. The proposed antenna is finally fabricated and measured, and the measured results show that the designed antenna exhibits low VSWR (<2), high gain (13 dBi~19.5 dBi) and high isolation (>25 dB) without beam splitting in the entire operation band.

A novel Vivaldi antenna with low radar cross section (RCS) for ultra-wide band (UWB) applications is proposed in this paper. As a printed antenna with electrically large length, the Vivaldi antenna has large backscattering when the incident waves are in the grazing directions. By sleeking the edges of the proposed antenna, the reflected currents are reduced so that the peaks of the backscattering can be inhibited. Its radiation characteristics are simulated and verified. The RCS performance of the proposed antenna is studied and compared with that of a commonly used Vivaldi antenna. The result shows that the proposed antenna has lower RCS than the reference antenna in both the perpendicular and grazing directions while maintaining similar radiation characteristics. So the results illuminate that the proposed Vivaldi antenna is a good candidate in the design of printed UWB end-fire antennas requiring low RCS.

In this paper, a novel high selectivity dual-band microwave bandpass filter (BPF) using dual-mode and triple-mode resonator is proposed. First, a dual-band filter comprising two dual-mode single band filters using common input/out lines is designed. Each single BPF is realized using a stepped-impedance resonator (SIR) with a centrally-loaded shunt open stub. The first and second passband can be independently controlled by the two dual-mode resonators, respectively. The proposed filter also offers three transmission zeros (TZs) to improve the selectivity. To further improve the selectivity over high side band of the first passband, a novel triple-mode resonator is designed to replace the dual-mode resonator. The basic structure of triple-mode resonator is microstrip-to-coplanar waveguide (CPW) structure. The microstrip structure provides one odd mode and one even mode resonator frequency and the CPW structure can provide another even mode resonant frequency without increasing circuit size. Both simulated and measured results show that the filters exhibit a good performance, including a small insertion loss, selectivity.

A unique-planar vialess Marchand balun for V-band application is presented. The balun can achieve less than 2° phase imbalance and 0.3 dB amplitude imbalance from 54 GHz to 66 GHz, with the insertion losses of -3.6 dB and -3.9 dB for the two balanced ports and the return loss of unbalanced port of less than -15 dB in the unbalanced port. The novel back-to-back measured method has been proposed and analyzed, the amplitude and phase imbalances can be derived from the measured back-to-back two-port scattering results. The extracted results achieve good agreement with the single balun simulation, no more than 0.15 dB and 1° amplitude and phase differences. This balun configuration and the measurement method can simplify the fabrication, achieve good yield, ease the assembling and decrease the cost.

We propose in this paper the design, realization and experimental characterization of a low-profile metamaterial ``bent'' monopole antenna with a total height of 0.027 λ<sub>0</sub> and a fractional bandwidth of 24.4% around 1.3 GHz. The metamaterial structure is a dual-layer mushroom-like electromagnetic band gap (DL-EBG) conceived and optimized to improve the antenna's operating bandwidth. Moreover, a ``Sabre-Type'' antenna composed by two identical ``bent'' monopole metamaterial antennas placed on both sides of a composite thin slab material has been simulated and realized. The ``sabre" antenna provides a vertically polarization and omnidirectional radiation patterns in the elevation plane while its radiation patterns are almost directional in the azimuth plane. A maximum gain of 8.7 dB is obtained by measurement at 1.45 GHz. A remarkable agreement is obtained between the measured and the simulated results.

This paper presents an efficient imaging algorithm for Terrain Observation by Progressive Scans (TOPS) mode SAR raw data focusing. First, the use of sub-aperture is adopted to overcome the aliased Doppler spectra due to progress azimuth beam scanning. Afterwards, range compression and range cell migration correction (RCMC) are individually implemented in each azimuth block with its individual Doppler centroid. After azimuth sub-aperture signal recombination, a new Doppler centroid varying rate is introduced to avoid the reconstructed Doppler spectra wrapping. Moreover, azimuth varying beam center time is removed by azimuth frequency scaling before the final azimuth spectrum analysis (SPECAN) step. Finally, the conventional Fourier transform (FT) is replaced by the scaled Fourier transform (SCFT) step to obtain the uniform azimuth space sampling interval. Since the proposed imaging algorithm is without any interpolations and azimuth data extension, it is highly efficient. Simulation results on point targets validate the proposed algorithm.

Within the generalized Lorenz-Mie theory framework, an analytic solution to the scattering by a conducting spheroid with non-confocal chiral coating, for incidence of an axial Gaussian beam, is presented. To overcome the difficulty of non-confocal boundary conditions, a theoretical procedure is developed by virtue of a transformation between the spherical and spheroidal vector wave functions. Numerical results of the normalized differential scattering cross section are shown for chiral-coated conducting spheroids.

In this paper, analytical field expressions are proposed to determine the electromagnetic fields due to an inclined lightning channel in the presence of a ground reflection at the striking point. The proposed method can support different current functions and models directly in the time domain without the need to apply any extra conversions. A set of measured electromagnetic fields associated with an inclined lightning channel from a triggered lightning experiment is used to evaluate the proposed field expressions. The results indicate that the peak of the electromagnetic fields is dependent on the channel angle, the observation point angle as well as the value of the ground reflection factor due to the difference between channel and ground impedances. Likewise, the effect of the channel parameters and the ground reflection on the values of the electromagnetic fields is considered and the results are discussed accordingly.

The design approach and development of a right hand circularly polarized wideband microstrip antenna for multi-constellation Global Navigation Satellite System (GNSS) is presented. The antenna is corner truncated square patch, parasitically excited by a dielectric covered straight probe. A thermacol layer of thickness λ/14 at center frequency is used to support the microstrip over the ground plane substrate. The simulated and measured results are presented. The antenna shows wide beam radiation patterns with axial ratio less than ± 1 dB. Its VSWR is better than 2.8:1 and the gain varies from 1.2 dBi to 3.5 dBi over the frequency band. L₅

The authors propose two 1×N all optical switches by taking the advantage of the accelerating behaviour of a spatial soliton in a Mach-Zehnder waveguide and the soliton's oscillating behaviour while propagating inside the nonlinear waveguide. The proposed switches consist of asymmetric and symmetric Mach-Zehnder waveguides followed by a homogenous Kerr medium, which is terminated by N parallel trapezoidal waveguides. In these switches, the signal is dropped from one of the desired output channels by changing the input pulse of wavelength or power. The numerical results confirm the switching application and show that the proposed 1×N switches can be used for wide ranges of wavelength and power, which are suitable for optical communication networks and optical data processing systems.

In the paper, the analysis of electromagnetic wave scattering from multilayered frequency selective surfaces is presented. The surface is composed of periodically arranged posts with irregular shapes. The multimodal scattering matrix of such structure is derived and the transmission and reflection characteristic for the structure with arbitrary plane wave illumination are calculated. The exact full-wave theory based on the hybrid approach employing mode-matching method and finite-difference frequency-domain (FDFD) technique is applied to develop an efficient theory to analyze such structures. The validity and accuracy of the approach are verified by comparing the results with those obtained from alternative methods and own measurements of manufactured periodic structures.

In this article, an optimized E-shaped patch antenna for Bluetooth (2.4-2.484 GHz) and UWB (3.1-10.6 GHz) applications with WLAN (5.15-5.825 GHz) band-notched characteristics is proposed. The dimensions of the E-shaped antenna structure in addition to the position of the slotted C-shape in the ground plane are optimized using recent optimization techniques such as Modified Particle Swarm Optimization (MPSO), Bacterial Swarm Optimization (BSO), and Central Force Optimization (CFO). The optimization algorithms were implemented using MATLAB-software and linked to the CST Microwave Studio to simulate the antenna. Next, the effects of the Laptop structure on the antenna radiation characteristics are considered. Finally, the antenna structures are simulated by the finite difference time domain method (FDTD) to validate the results. The measured results exhibit good agreement with the simulation from CST and the Finite Difference Time Domain (FDTD) program written with matlab.

A novel cross-coupled resonator filter with multilayer structure is presented in this paper. By using enhanced inner coupling structure and 3D layout, the resonator size is largely reduced, and high spurious frequency could be achieved. To validate the proposed topology, a cross-coupled 3D filter with inner coupling capacitor is easily fabricated on a normal printed circuit board. The measured results show the characteristics of small size, good stopband performance and high spurious frequency.

The intermittent sampling repeater jamming (ISRJ) can only produce fake point scatterers in the down-range, while the time-varying frequency induced by rotational micro-motion dynamics blurs the image in the cross-range. This paper focuses on the combination of the above two methods to counter the inverse synthetic aperture radar (ISAR). Based on the signal models of coherent ISAR signal processing, principles of the jamming are derived. The key jamming parameters and the selection criteria are determined by two steps. Finally, the validity of the proposed algorithm is demonstrated using the numeric simulations and simulations based on the measured data.

The thickness measurement of concrete is one of the most important commercial applications of ground-penetrating radar (GPR) technique. This paper describes a procedure for estimating the thickness of concrete slab for different moisture contents (MCs) in frequency domain, as in Impulse-Response (IR) Method, over the radar frequency band 100 MHz-2 GHz). The method is based on predicting the reflected frequency spectrum through a concrete slab using Jonscher model. The procedure is explained and examples of results are presented.

To simulate the beam and wave interaction (BWI) of various types of traveling wave tube amplifiers (TWTAs), a digitized nonlinear theory has been developed with two features. Firstly, the digitized RF field profiles obtained from electromagnetic simulation software are applied to replace the analytical RF field profiles in TWTAs. Secondly, the relationship of energy conservation between the beam and RF fields is used to derive the RF field equations. Based on this nonlinear theory, onedimensional code has been constructed to predict the performances of TWTAs. Comparisons between the simulations and the experimental results for a K-band helix TWTA, a V-band coupled cavity (CC) TWTA and a W-band folded waveguide (FWG) TWTA are made and discussed to prove the validation of this nonlinear theory.

A rotationally symmetric short-circuited stub-loaded structure is proposed to design a microstrip-line bandpass filter with two transmission zeros near the lower and upper cut-off frequency edges of operating millimeter-wave bands. Furthermore, interdigital coupled-lines and additional resonators are integrated into the proposed rotationally symmetric bandpass filter to improve the out-of-band rejection. as design examples, the in-band and out-of-band performances of two filter prototypes using single layer microstrip-lines are designed and experimentally examined. the measured results show that the filter without any interdigital coupled-lines achieves a passband insertion loss of 0.97 dB at 40 GHz and out-of-band rejection of larger than 23 dB, while the filter with the interdigital coupled-lines realizes the suppressions in lower and upper-bands of, respectively, larger than 30 dB and 19 dB for the overall insertion loss of 2.1 dB at 40 GHz.

We consider three different definitions of magnetic dipole moment for electrically neutral compact bunches of charged particles and show that, in general, they are not equivalent to each other with respect to their relativistic transformation. In particular, we prove that the "configurational" definition of magnetic dipole moment m_c = 1/2∫_v(r × j)dV (in the common designations) and its definition through generated electromagnetic field ("source" definition m_s) or experienced force ("force" definition m_f) lead to different relativistic transformations of m_c and m_s (m_f). The results obtained shed light on the available disagreements with respect to relativistic transformation of a magnetic dipole moment, and they can be used in covariant formulation of classical electrodynamics in material media.

In this paper, we report a new design of a compact antenna based on the use of split ring resonator (SRR). The designed antenna consists of two SRRs, with the same geometrical parameters, printed symmetrically on both sides of the dielectric substrate. Excitation of the SRR element is performed by adequately placing the access microstrip lines with respect to the confinement plane of the split rings. The resonance frequency of the antenna is essentially defined by geometrical parameters of the SRR, which makes it suitable for a broad range of applications spanning from mobile terminals to WLAN and WPAN systems. The final result is low profile, and can be easily integrated with other RF front-end circuits in a PCB.