An accurate and efficient formulation is presented for the electromagnetic analysis of dielectric waveguide gratings under plane-wave conical incidence. An arbitrary number of dielectric bars can be placed inside each one-dimension periodic cell, including the effect of dielectric losses. The reflectance of a dielectric waveguide grating under conical incidence is compared with theoretical results presented by other authors, finding a very good agreement. A single-layer reflection filter has been designed centered at λ₀=1.5 μm whose spectral and angular responses are shown. For this structure, the effect of the asymmetry of the distribution of the refraction index in the reflectance has been analyzed, observing a splitting of the reflection peak around the design wavelength. Finally it is discussed the equivalence between a volume grating and a shallow surface-relief grating, providing two examples of designing prescriptions.

In this paper, we study the bistatic reflection and transmission properties of random rough surface with large slope and large height. Method of Moment (MOM) is used to solve the surface integral equations for 2D rough surface scattering problem. The modeled rough surfaces are similar to random rectangular grating, so that there are large slopes on the surface. The motivation of the study is to analyze scattering by sastrugi surface in Polar Regions. The ridges on the sastrugi surface have heights of about 20 cm. In microwave remote sensing of land at 5 GHz, 10 GHz, 19 GHz and 37 GHz, these heights are larger than wavelength. Next, we consider the scattering problem of the sastrugi rough surface over multi-layered snow. The bistatic reflection and transmission coefficients from MOM solutions are used as the boundary conditions for multi-layered radiative transfer equations. The radiative transfer equations are solved and the reflectivities are calculated. Numerical results are illustrated as a function of roughness and multi-layered parameters. We demonstrate that rough surface of sastugi, when interactions with layered media, causes increase in reflectivity and the decrease in emissivity. The increase of reflectivity can be attributed to the fact that rough surface with large slope facilitates large angle transmission. The large angle transmission results in increase of subsurface reflection and the possibility of total internal reflection in layered media below the rough surface.

A method based on plant growth simulation algorithm (PGSA) is presented for pattern nulling by controlling only the element amplitudes of linear antenna array. The PGSA is a new and highly efficient random search algorithm inspired by the growth process of plant phototropism. Simulation results for Chebyshev patterns with the imposed single, multiple and broad nulls are given to show the performance of the proposed method.

A planar, circular monopole antenna (PCMA) with satisfactory radiation characteristics over an ultra-broadband is demonstrated. Compared to the classical coplanar-waveguide (CPW) fed PCMA, the radiation characteristics of the proposed CPW-fed PCMA are significantly improved, particularly at the frequencies around the higher band edge. This improvement is achieved by exploiting a tapered and periodically corrugated edge design to the CPW ground plane. The tapered and corrugated ground-plane edge design, in essence, modifies the current distribution on the circular disc as well as along the edges of the ground plane. With this design, the cross polarization radiation is remarkably reduced, and the pattern deterioration, especially at the planes perpendicular to the plane of the antenna, is greatly alleviated. The demonstrated CPW-fed PCMA features an over 150 % VSWR=2 fractional bandwidth (0.81-5.87 GHz) and promises satisfactory radiation characteristics over the entire band. The proposed PCMA is poised for applications in wideband/ultra-wideband communication systems.

In this paper, the conformal finite-difference time-domain (CFDTD) method using PSO optimization is applied to design a compact directive balanced antipodal Vivaldi antenna for ultra-wideband (UWB) applications. This paper demonstrates miniaturized antipodal Vivaldi antenna (32 × 35 × 1.6 mm³), having low-cross polarization levels and reasonable gain from 3.1 to 10.6 GHz. The antenna peak gain is 5.25 dBi in the specified band. The simulated and experimental results of return loss, far field patterns and gain are presented.

We provide here a theoretical description of electromagnetic scattering by multi-wall carbon nanotubes based on an effective-boundary condition derived previously using a phenomenological quantum model. We present the basic analytical solution, extending it then to include the electromangetic interaction between multiple concentric tubes in the general multi-wall carbon nanotube case.

The design, simulation and performance enhancement of a new structure for X-band high-power, low-loss, low-bias, triangular-ferrite waveguide circulator are presented. Dual circulation property is obtained by triangular shape of ferrite post. The effects of circulator's structure parameters, such as ferrite parameters and magnetic DC bias, on isolation, insertion loss and return loss of circulator are discussed. The HFSS software is used for simulating the circulators. Final dual band designs with 20 dB return loss, 20 dB isolation and 0:1 dB insertion loss in dual frequency in X-band (8:2 GHz and 10:4 GHz) with only a magnetic bias of 10 Oe are obtained.

Multiple-input multiple-output (MIMO) systems play a vital role in fourth generation wireless systems to provide advanced data rate. In this paper, a better performance and reduced complexity channel estimation method is proposed for MIMO systems based on matrix factorization. This technique is applied on training based least squares (LS) channel estimation for performance improvement. Experimentation results indicate that the proposed method not only alleviates the performance of MIMO channel estimation but also significantly reduces the complexity caused by matrix inversion. The performance evaluations are validated through computer simulations using MATLAB® 7.0 in terms of bit error rate (BER). Simulation results show that the BER performance and complexity of the proposed method clearly outperforms the conventional LS channel estimation method.

We report fast and accurate simulations of metamaterial structures constructed with large numbers of unit cells containing split-ring resonators and thin wires. Scattering problems involving various metamaterial walls are formulated rigorously using the electric-field integral equation, discretized with the Rao-Wilton-Glisson basis functions. Resulting dense matrix equations are solved iteratively, where the matrix-vector multiplications are performed efficiently with the multilevel fast multipole algorithm. For rapid solutions at resonance frequencies, convergence of the iterations is accelerated by using robust preconditioning techniques, such as the sparse-approximate-inverse preconditioner. Without resorting to homogenization approximations and periodicity assumptions, we are able to obtain accurate solutions of realistic metamaterial problems discretized with millions of unknowns.

In the present paper notch loaded shorted microstrip patch antenna has been analysed using cavity model. The proposed antenna shows dual band operation which depends on notch dimensions as well as shorting wall. The frequency ratio is found to be 1.5278 for the notch loaded rectangular patch, while in notch loaded shorted patch, the frequency ratio varies from 2.9764 to 2.725 for increasing value of notch width and it is almost invariant with notch depth. Further a slot loaded shorted patch antenna shows the dual frequency nature with the frequency ratio1.7. The theoretical results are compared with IE3D simulation as well as reported experimental results.

By employing Microelectromechanical system (MEMS) technology, Fabry Perot Optical Tunable Filter (FPOTF) with hybrid tuning mechanism, varying d and altering incident angle is presented. The proposed structure consists of a floating dual membrane FPOTF with capability to be tuned at different light incident angles. Three electrostatic cavities have been designed to perform this task independently. This technique is capable to increase the tuning range up to 2/3 of capacitance gap with additional doubly range of incident angle. Optic, mechanic and electrostatic analysis of the proposed structure has been validated by simulation. Analysis in optical performance shows the tuning range enhancement is about 1.92% for +/-2^o mirror tilting at 6^o initial angle compared to conventional dual beam MEMS FPOTF. This analysis validates the principle of hybrid tuning method.

Nowadays, through wall imaging (TWI) is a emerging topic of research in which one of the most important tasks is to minimize the clutter through which detection accuracy can be improved. Clutter in TWI is due to many reasons like wall coupling, antenna coupling, multiple reflections etc. To analyze the clutter reduction techniques, firstly we indigenously assembled a TWI system (i.e. step frequency continuous wave radar (SFCW)) in UWB range (freq. 3.95 GHz to 5.85 GHz), and different observations have been taken. We have considered metallic plate and one more material with low dielectric constant (Teflon) as a target and kept them behind the plywood wall. A-scan and B-scan observations have been carried out. The observed data are preprocessed for imaging and then different types of clutter reduction techniques like Principal Component Analysis (PCA), Independent Component Analysis (ICA), Factor Analysis (FA) and Singular Value Decomposition (SVD) have been applied, and results were analyzed. Signal to noise ratio (SNR) of the final images (i.e., after clutter removal with different techniques) has been computed to compare the results and know the effectiveness of individual clutter removal techniques. It is observed that ICA has better capability to remove the clutter in comparison to other applied techniques; especially it is found that ICA has a capability to distinguish the difference between clutter and low dielectric target whereas other clutter removal techniques are not showing significant result.

A compact, ultra-broadband coplanar-waveguide (CPW) bandpass filter (BPF) is demonstrated. The proposed CPW-BPF is essentially designed by exploiting CPW short-stub and open-stub structures. Technically, the proposed filter comprises shunt short-stub and series open-stub structures that are connected in a cascade topology. The higher and lower cutoff frequencies are mainly related to the electrical length of the shunt short stub and the series open stub, respectively. In addition, the stopband rejection is enhanced through an incorporation of CPW bandstop structures. The proposed filter design is verified through experimental demonstration. The corresponding lumped equivalent and transmission-line equivalent circuits are provided for circuit design purpose. Compared with the classical CPW-BPFs, the proposed filter is of a relatively simple and compact configuration. The demonstrated CPW-BPF has about 110% 3-dB fractional bandwidth, sharp selectivity, and great stopband rejection.

In this paper, Enhanced Practical Swarm Optimization (EPSO) algorithm is proposed to be applied to pattern synthesis of linear arrays. Updating formulas of global best particle position and velocity are modified to improve the convergence accuracy of classical Practical Swarm Optimization. The developed EPSO is tested and compared with a standard benchmark to be validated as an efficient optimization tool for beamforming applications. Different numerical examples are presented to illustrate the capability of EPSO for pattern synthesis with a prescribed wide nulls locations and depths. Collective multiple deep nulls approach and direct weights perturbations approach are considered to obtain adaptive wide null steering subject to peak side lobe level and minimum main beam width constraints. Starting from initial chebyshev pattern, single or multiple wide nulls are achieved by optimum perturbations of elements current amplitude or complex weights to have either symmetric or asymmetric nulls about the main beam. Proper formation of the cost function is presented for all case studies as a key factor to include the pattern constraints in the optimization process.

Ray-tracing exercise and full-wave analysis were performed to validate the performance of a type of cloak composed of isotropic metamaterials. It is shown that objects inside the 'folded region' of this cloak appear invisible to the incoming light from a ray tracing exercise, but exhibit magnified and shifted scattering under a plane wave illumination from a full wave analysis. Gaussian beams are introduced to resolve this interesting paradox resulted from these two methods. We show that at the time-harmonic state, small energy can be diffracted into the folded region and contribute to the resonant state even when the Gaussian beam is steered away from the cloak with an object inside. A scattering pattern identical to that scattered from the image of the object will be formed, which agrees well with the phenomenon in the plane wave incidence case.

A novel fractal tag antenna constructed with Hilbert-curve and self-complementary configuration is proposed for UHF RFID applications. The main aim of this paper is to merge the meander line and meandered-slot structure of the RFID tag antenna in order to obtain a good performance of compact, broadband, circular polarization and conjugate impedance matching. The tunable inductive and broadband (-10 dB BW = 115 MHz) characteristics of frequency responses and directivity (1.62 dBi) as well as circular polarization (-3dB AR BW = 315 MHz) of radiation patterns for 900 MHz are studied and presented.

In this paper, a triple-band printed dipole tag antenna is proposed for Radio Frequency Identification (RFID). The triple-band printed dipole antenna is designed to operate at 0.92 GHz, 2.45 GHz and 5.8 GHz using Computer Simulation Technology (CST) software. In order to achieve triple-band operation, the proposed antenna contains two branch elements, which act as an additional resonator. The designed antenna is fabricated using Taconic RF-35 substrate with a dielectric constant (ε_r) of 3.5 and thickness (d) of 0.508 mm. The antenna's parameters for triple-band operation are investigated and discussed. Then, this fabricated antenna is integrated with a UHF microchip to become a passive UHF tag. This tag is tested by measuring the reading distance and it is found that the proposed tag can be used for RFID application.

In this paper, a new kind of 3D transition and power divider based on half mode substrate integrated circular cavity (HSICC) is proposed. This novel HSICC transition and power divider can be easily integrated into microwave and millimeter-wave multilayer circuits using LTCC technology. What is more, it can reduce nearly half size of normal SICC resonator and has the advantages of high flexibility, low insertion loss and amplitude imbalance. Two different 3D simulation tools are employed to validate the design method of this novel structure.

The passing center swing back grids (PCSBG) technique, in conjunction with the method of characteristics (MOC), was proposed to model electromagnetic problems featured with rotating objects. The drive of this proposal lays mainly on the fact that MOC defines all field components in the center of grid cell. Its practicability was validated by exhibiting the radiated EM fields from a rotating cylinder which carries surface currents with Gaussian profile and flowing in the axial direction. To clearly demonstrate that the cylinder is rotating and radiating EM fields simultaneously, the following arrangements were made. The cylinder may be equally sliced into an even number of segments that are with and without currents alternatively since a rotating circular cylinder yields no relativistic effects. The computational results showed that the radiated electromagnetic fields bear vortex structures as the cause of rotating cylinder, which serves as the evidences that PCSBG works properly.

μThe surface wave modes in the chiral negative refraction grounded slab waveguides in which the slab or cladding consists of chiral negative refraction metamaterial are investigated. The dispersion relations, electromagnetic fields, energy flow distribution and the total power of surface wave modes are presented. Some novel features have been found. The energy flow of surface wave mode is in opposite directions in the core and cladding. The total power is negative (corresponds to backward wave) in the grounded chiral negative refraction metamaterial slab waveguides.