The dynamics of a system comprising of two bilaterally coupled Gunn oscillators (BCGOs) has been examined using a circuit theoretic model of the Gunn oscillator (GO). The effects of coupling factors (k_ij) between i-th and j-th oscillators on the frequency-range of synchronized operation and the magnitude of common frequency of oscillation have been examined semi-analytically and by numerical solution of the system equations. The occurrence of chaotic oscillations at the verge of synchronization bands is observed in numerical simulation. The experimental response of the BCGO operating in the X-band is obtained and the results are found to be qualitatively similar to the analytical and numerical predictions.

A novel and compact dual-mode defected ground structure (DGS) resonator is presented. Distinct characteristics of the proposed resonator are investigated. Using this type of resonator, a bandpass filter with the center frequency of 2.38 GHz and the fractional bandwidth of 6.7% is simulated and fabricated. The results show that this filter not only has an inherent transmission zero near the passband, but also has a very wide upper stopband with rejection better than 20 dB up to about 12 GHz.

To accurately model nanophotonic structures, a conformal dispersive finite difference time domain (FDTD) method based on an effective permittivity technique is presented, which can describe exactly the behaviors of evanescent waves in the vicinity of curved interface. A mismatch between the numerical permittivity and the analytical value introduced by the discretization in FDTD is demonstrated, thus, very fine time-step size is always necessary for nanostructures modelling, which greatly increases the required overheads of CPU time as compared to usual FDTD simulations. To resolve this problem, the performance of parallel FDTD code is investigated on a Gigabit Ethernet, and the acceleration technique for parallel FDTD algorithm is presented, which is developed by means of the replicating computation based on overlapping grids, the OpenMP multithreading technique and the vectorization based on SSE instruction. The comparison of relevant numerical results shows that these methods are able to reduce the expense of the system communications and enhance the utilization ratio of the CPU effectively, which improves greatly the performance of parallel FDTD with high time-consuming.

In this paper, modeling and experimentation of a Rectangular Patch Resonator (RPR) covered with a dielectric superstrate are investigated. The RPR criteria are established theoretically and experimentally, to be used in future prospects as an electromagnetic (EM) sensor for the characterization of superstrates. The theoretical model is based on the moment method (MoM) via Galerkin's approach, in which three types of basis and testing functions are used. These functions as well as the spectral dyadic Green function are efficiently implanted with compact structured Fortran 90 codes. The EM commercial HFSS and CST Microwave Studio softwares are used to simulate the proposed RPR prototypes. The accuracy of the obtained results is assessed using four prototypes of RPRs operating around 6 GHz, taking into account only the resonant frequency of the fundamental dominant mode. The theoretical model is compared to simulation and measurement results, and very good agreements are observed.

A Z-R relation is derived using a data set which consists of nine rain events selected from Singapore's drop size distribution. Rain events are separated into convective and stratiform types of rain using two methods: the Gamache-Houze method, a simple threshold technique, and the Atlas-Ulbrich method. In the Atlas-Ulbrich method, the variability of the rain integral parameters R, Z, N_w, D₀ and gamma model parameter $\mu $ are used for the classification of rain into convective, stratiform and transition. Z-R relations are derived for each type of rain after classification. The changes in the coefficients of the Z-R relations for different rain events are plotted and analyzed. The Z-R relations of the different methods using the Singapore data are compared and analyzed. It is concluded that the coefficient A of the Z-R relation is higher for the convective stage followed by the stratiform and transition stages. The coefficient b values are higher for the transition stage followed by the stratiform and convective stages. Reflectivities are extracted from RADAR data above NTU site for rain events and compared with the reflectivities derived from the distrometer data. Rain rates retrieved from RADAR data using the proposed relations from Singapore's data set are compared with the distrometer rain rates. The RADAR extracted rain rates are found to be constantly lower than the distrometer derived rain rates but matches well.

A novel Ultra Wideband (UWB) antenna on double substrates crossing is presented in this paper. Based on conical antenna and microstrip patch UWB antenna, the proposed antenna is omni-directional, band-notched and easy to be fabricated. It operates from 2.6 GHz to 12 GHz with low Voltage Standing Wave Ratio (VSWR<2), excluding a notch-band of 5.8 GHz. Except for good performance of VSWR, the proposed antenna keeps its radiating beam at about θ = 45°in E-plane through the whole band. The UWB antenna is fed by a coaxial probe through a SMA connector. The length of the proposed monopole element above the ground is slightly less than λ/4 of the lowest frequency. The simulated and measured results of the VSWR, he gain and the radiation patterns for the proposed antennas are presented and discussed. Good agreement between simulated and measured results is demonstrated.

A new three dimensional conical ground plane electromagnetic cloak is proposed and designed based on the coordinate transformation of Maxwell's equations. Material parameters of the conical invisible cloak are derived which have simple form and lesser inhomogeneity compared with other 3-dimensional cloaks. Because of convenient form of the constitutive tensors of the conical cloak, we propose a new strategy for homogeneous approximation of the materials of the cloaks. Numerical simulations confirm that approximation with eight slices, is more than enough and this cloak can hide any object on the ground as well as inhomogeneous ones.

A wide analysis of left-handed material (LHM) spheres with different constitutive parameters has been carried out employing different integral-equation formulations based on the Method of Moments. The study is focused on the accuracy assessment of formulations combining normal equations (combined normal formulation, CNF), tangential equations (combined tangential formulation, CTF, and Poggio-Miller-Chang-Harrington-Wu-Tsai formulation, PMCHWT) and both of them (electric and magnetic current combined field integral equation, JMCFIE) when dealing with LHM's. Relevant and informative features as the condition number, the eigenvalues distribution and the iterative response are analyzed. The obtained results show up the suitability of the JMCFIE for this kind of analysis in contrast with the unreliable behavior of the other approaches.

We propose a three-dimensional directional cloak for arbitrarily polarized incoming electromagnetic waves, motivated by the fact that there will be negligible scattering when the direction of impinging wave coincides with the axial direction of a very thin and elongated perfectly electric conducting (PEC) scatterer. The performance of the cloak under different polarizations of incoming waves are numerically investigated. The case in which the direction of incoming wave is perturbed off the ideal direction is also quantitatively studied. Numerical simulations show that the directional cloaking device is able to tolerate a large range of tilted angles of incoming waves.

An innovative radar imaging system, based on the capability of a fixed UWB array to radiate short pulses in different directions along time with the principle of electronic beam steering, is presented in this paper. To demonstrate its concept, the analysis presented in this paper is based on simulation results. As function of the use of either only one antenna or several antennas in reception, two radar imaging algorithms have been developed and are detailed in this paper. These algorithms permit to obtain an image of the analyzed scene thanks to the transient beam pattern of the array used in emission. Finally, with a same analyzed scene, these algorithms have been compared with the time reversal method and the back projection algorithm, in association with a SAR imaging system. The conditions of applicability of these methods are also discussed.

The performance degradation in traditional adaptive beamformers can be attributed to the imprecise knowledge of the array steering vector and inaccurate estimation of the covariance matrix. The inaccurate estimation of the covariance matrix is due to the limited data samples and presence of desired signal components in the training data. The mismatch between the actual and presumed steering vectors can be mainly due to the error in the look direction estimate. In this paper, we propose a novel algorithm to estimate the look direction and to reconstruct the covariance matrix so that near optimal performance without the effect of saturation can be achieved as the input SNR increases. Numerical results also show that all existing beamforming algorithms suffer from saturation effect as the input SNR increases.

The increase in mobile communications traffic has led to heightened interest in the use of ray tracing (RT) methods together with digital building databases for obtaining more accurate and efficient propagation prediction in urban microcellular environments. In this paper, a novel quasi three-dimensional (3-D) RT algorithm is presented by taking into account the advantages of both the image theory (IT) and the shooting-and- bouncing ray (SBR) method. It is based on creating a new virtual source tree in which the relationship between neighbor nodes is a left-son-and-right-brother one. Our theoretical results of the signal path loss along the streets are compared with measurements which have been reported for city streets in Tokyo and Ottawa City for various values of the propagation parameters. The good agreement with these measurements indicates that our prediction model works well for such microcellular communication applications. The proposed method can provide the reliable theory basis for radio-wave propagation prediction and network planning in urban microcellular environments.

The TM₀ surface mode in an infinitely long parallel-plate waveguide filled with a double-positive (DPS) and epsilon-negative (ENG) metamaterial bi-layer is studied. With proper constitutive parameters and thicknesses of the two layers, the slow-wave factor (SWF) for such a parallel-plate waveguide can tend to infinity as the frequency decreases. A 2-D cavity based on the DPS-ENG bi-layer waveguide is constructed and studied to evaluate the radiation ability of its corresponding patch antenna. Based on the cavity model analysis of patch antennas, we show that good efficiency for broadside radiation of such a cavity-based rectangular patch antenna can be achieved when one layer of the cavity is shielded (or partially shielded) by PEC boundaries. Taking practical loss and dispersion into consideration, a miniaturized cavity-based rectangular patch antenna is proposed as an example. With the super-slow TM₀ surface mode excited in the bi-layer by a simple coaxial line feeding, the antenna has a dimension of only 0.107λ₀×0.129λ₀×0.045λ₀. The patch antenna produces broadside radiation, and fairly good radiation efficiency is achieved. The PEC-Partially-Shielded-ENG-Cavity based rectangular patch antenna with a further miniaturization but reduced radiation efficiency is also discussed.

The homogeneity of the amplitude of one of the polarizations of the RF field B₁ is a crucial issue in Magnetic Resonance Imaging (MRI), and several methods have been proposed for enhancing this uniformity (``Shimming''). The existing approaches aim at controlling the homogeneity of B⁺₁ and limiting the Specific Absorption Rate (SAR) of the RF field by independently controlling magnitude and phase of individual excitation currents in MRI scanners, either birdcage or TEM coil system. A novel approach is presented here which allows a joint control of B⁺₁ uniformity, SAR, and purity of polarization of the total RF B₁ field. We propose a convex optimization procedure with convex constraints, and special attention has been devoted to the issue of convexity of the proposed functional. The method is applied to MRI brain imaging; numerical tests have been performed on a realistic head model at low, medium, and high RF field in order to assess the effectiveness of the proposed method. We found that maintaining a specific polarization plays an important role also in maintaining the homogeneity of B⁺₁ amplitude.

Simple normalized dispersion relations for transverse magnetic (TM) and transverse electric (TE) propagating modes in parallel-plate waveguides filled with DPS/DPS or DNG/DNG, and DNG/DPS bilayers are presented. The evanescent TE₀ mode of the waveguide filled with a DNG/DPS bilayer is characterized also by a simple normalized dispersion relation. Since an important behavior of the modes in the waveguide filled with a DNG/DPS bilayer is the existence of a turning point (TP) at which the power carried by the respective mode on the propagation direction equals zero and changes the sign, we present also implicit relations for determining the normalized parameters of the TM and TE modes at that TP. We show that the TP begins to exist at certain values of the normalized parameter v₂ characterizing the DPS layer. For both the TM and TE modes, the higher is the mode order, the greater is the v₂ parameter at which the TP begins to exist, but the behavior of the TP is different for the TM and TE modes.

In this work, we analyze modified bowtie nanoantennas with polynomial sides in the excitation and emission regimes. In the excitation regime, the antennas are illuminated by an incident plane wave, and in the emission regime, the excitation is fulfilled by infinitesimal electric dipole positioned in the gap of the nanoantennas. Several antennas with different sizes and polynomial order were numerically analyzed by method of moments. The results show that these novel antennas possess a controllable resonance by the polynomial order and good characteristics of near field enhancement and confinement for applications in enhancement of spontaneous emission of a single molecule.

Modeling of a ferroelectric interdigital capacitor (IDC) and its incorporating in composite right/left-handed (CRLH) unit cells is represented. To evaluate the capacitance of a multi-layered IDC structures, conformal mapping and partial capacitance methods are utilized. Furthermore, the partial displacement method is utilized to calculate the electric field distribution and the its relation in the ferroelectric layer to applied voltage is obtained. Using this relation in a phenomenological model, dependency of the relative permittivity of ferroelectric on the applied voltage is obtained. The designed unit cell is comprised of IDCs and spiral inductors. To alter the propagation constant of the unit cell by varying the applied voltage, a thin layer ofBa_0.5Sr_0.5TiO₃ (BST-0.5) ferroelectric is incorporated underneath an IDC, called BST-0.5 varactor. The periodic structure based on the designed unit cell leads to a CRLH LWA. The Tunability of the periodic structure with three unit cell is demonstrated by varying the relative permittivity of the ferroelectric layer.

In the present paper, we deal with the performance analysis of the Adaptive Normalized Matched Filter (ANMF) detector in compound-Gaussian clutter with inverse gamma texture model and unknown covariance matrix. First, the maximum likelihood estimate (MLE) of the covariance matrix for this clutter model is derived. The MLE is then plugged into the ANMF test and compared to the well known normalized sample covariance matrix estimate (NSCM) and the approximate maximum likelihood estimate (AML). The performance in terms of CFAR behavior and detection probability is evaluated in the presence of simulated clutter and real sea clutter data, which is collected by the McMaster IPIX radar.

A novel multipolarized sectoral antenna on a metallic electromagnetic band gap (M-EBG) surface is investigated. The M-EBG structure behaves as a partially reflecting surface (PRS) and enhances the directivity of a simple radiating source. The use of metallic structures offers a new approach to industrial partners in order to reduce costs and to facilitate design techniques. By using double layers of M-EBG structure working on orthogonal polarizations as a superstrate with a single patch feeding by two ports, multipolarization operation is achieved. This antenna provides vertical, horizontal, 0°/90°and circular polarizations with a sectoral radiation pattern in the azimuth plane. M-EBG antennas with sectoral pattern are usually designed only for vertical polarization. In order to verify the results a Bipolar M-EBG Sectoral antenna prototype for WIMAX application~[5.15-5.35] GHz is realized and measured. Finally, we study the possibility to generate circular polarization.

The simulation of nonlinear loaded high-speed microstrip interconnects by means of a convolution-based procedure is described when both, analytical and measured scattering parameters are used. Closed-form equations are employed to obtain the analytical scattering parameters. The influence of measured scattering parameters, when these are used instead the analytical ones, is investigated to know how the microstrip interconnect responses are affected. The convolution procedure is complemented by including the transmission line linear equation and the microwave circuit reflection theory. S