In this paper, the dispersive properties and switching state of three-dimensional (3D) photonic crystals (PCs) with diamond lattices, which are composed of the core isotropic dielectric spheres with surrounded by the epsilon-negative (ENG) materials shells inserted in the isotropic dielectric background (air), are theoretically investigated in detail based on a modified plane wave expansion method. The wavelength division multiplexer can be realized easily by tuning the switching state of such PCs. The equations for computing band structures for such 3D PCs are presented. Our analysis shows that the proposed double-shell structures can obtain the complete photonic band gaps (PBGs) which can be realized optical switching with on or off states by manipulating the radius of core dielectric sphere, the relative dielectric constant of background, the dielectric constant of ENG materials and the electronic plasma frequency, respectively. However, the thickness of the ENG materials shell cannot change the switching state as the radius of core dielectric sphere is certain. Numerical simulations also show that a flatbands region, and the stop band gaps (SBGs) in (1 0 0) and (1 1 1) directions which are above the flatbands region can be achieved. The SBGs in (1 0 0) and (1 1 1) directions can also be tuned by the parameters as mentioned above. There also exists a threshold value for the thickness of ENG material shell, which can make the band structures for the 3D PCs with double-shell structures similar to those obtained from the same structure containing the pure ENG materials spheres. In this case, the dielectric function of inserted core sphere will not affect the band structures. It means that we can achieve the PBGs by replacing the pure ENG materials spheres with such double-shell structures to make fabricate easily and save the material in the realization. It is also noticed that the flatband region is determined by the existence of surface plasmon modes, and the upper edge of flatband region does not depend on the topology of lattice. Such presented 3D PCs with double-shell structures offer a novel way to realize the wavelength division multiplexers.

In time-modulated antenna arrays (TMAAs), as a result of periodical switch-on and switch-off of the antenna elements, including operating frequency (termed as center frequency) signal, sideband signals are appeared at either sides of the center frequency in integer multiples of the modulation frequency. In this paper, it is shown that without using phase shifters, just by suitably controlling the on-time instants (OTIs)and on-time durations (OTDs) of a timemodulated linear antenna array (TMLAA) elements, simultaneously, along with a pencil beam pattern at the operating frequency, a shaped beam pattern can be obtained at both the first positive and negative harmonics of the time-modulation frequency. The important advantage of such a technique is that realization of multi-beam pattern in conventional antenna array (CAA) system generally requires complex feed network, whereas by using simple radio frequency (RF) switching circuit in the feed network of TMLAA, by virtue of the properties of harmonic radiations, synthesis of a shaped pattern at either (positive or negative) harmonic results in generating the same pattern in its opposite harmonic, and the synthesized patterns at different harmonics can be simultaneously used as independent communication channels. By employing a differential evolution (DE) based optimization method, numerical results for a 16-element TMLAA with uniform excitation show that in conjunction with a pencil beam pattern at the center frequency, a flat-top or a cosec square pattern at first positive and negative sidebands of side-lobe levels (SLL) -20 dB can be synthesized by suppressing the higher sideband level (SBL) to below -10 dB.

The focusing of a magnetic field, at low frequencies, in the very near field is difficult as flux lines naturally tend to disperse. It is not possible to use antenna array techniques due to large wavelengths at low frequencies. A method for synthesizing a concentrated magnetic field in a large air gap between two magnetic poles is presented. The focusing effect is brought about by the inclusion of side poles, adjacent to each of the main poles. Through the correct dimensioning of the side poles' reluctances and relative magneto-motive forces it is possible to focus the field in the center of the gap. General design curves for normalized parameters, determined via finite element modelling, are presented. A scale model is experimentally verified.

We present a robust multiple-channel vector-matching localization approach (MCVM) based on signal strength difference (SSD) fingerprinting of ZigBee Network. Compared with some existing algorithms, our presented approach has threefold advantages: firstly, far fewer numbers of received signal strength(RSS) measurements and reference nodes are needed; secondly, it shows more robustness to the fluctuation of RSS; thirdly, it requires low time-consuming signal strength collection surveys in the location space. We demonstrate the performances of our algorithm experimentally using different numbers of channels, reference nodes and training points. The Cramer-Rao Low Bound(CRLB) of SSD is derived in order to compare the performance of the different localization methods addressed. The experiment results show the efficacy of our proposed approach.

In this paper, a broadband class-F^-1 power amplifier (PA) that can be integrated into compact-sized micro-radio units is introduced. This PA utilizes a multi-harmonic impedance merging technique at harmonic frequencies so that the circuit areas of matching networks can be minimized. As well, in order to maximize the bandwidth of high efficiency, circuit configuration was optimized by the first order differentiation of the fundamental-frequency impedance. For the sake of verification, a 10 W inverse class-F PA operating at 1.9 GHz was designed with a commercial GaN transistor. It exhibited a 39.2% size reduction as compared to conventional PAs of the similar power. In addition, it exhibited a bandwidth of 600 MHz (1.6 ~ 2.2 GHz) at an efficiency greater than 60%, a peak efficiency of 83.9%, and an output power of 42.2 dBm.

A novel (2x2) high-gain circularly-polarized cylindrical dielectric resonator antenna array integrated with helical exciter is proposed. The array offers a maximum gain of 13.8 dBi at the operating frequency. The circular polarization is obtained by incorporating helical exciter in the array structure. A prototype of the proposed configuration integrated with helical exciter has been fabricated, tested and the idea has been verified. A good agreement has been obtained between the measured and the simulated results.

Polarization and incident angle independent metamaterial-based absorber (MA) which acts as a strong dual-band resonator is designed and constructed. Besides, a method to design single/dual-band MA is presented in detail. The proposed model is based on isotropic ring resonator with gaps and octa-star strip (OSS) which allows maximization in the absorption because of the characteristic features of the structure. Reflection and absorption responses are obtained both numerically and experimentally and compared to each other. Two maxima in the absorption are experimentally obtained around 90% at 4.42 GHz for the first band and 99.7% at 5.62 GHz for the second band which are in good agreement with the numerical simulations (95.6% and 99.9%, respectively). The numerical studies verify that the dual-band MA can provide perfect absorption at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves. The proposed model can easily be used in many potential application areas such as security systems, sensors, medical imaging technology.

Inductive-coupling scheme for microstrip bandpass filters with quarter-wavelength stepped-impedance resonators is proposed. This is realized by a short-end stub which behaves as a K-inverter. It is investigated that the coupling coefficient of the resonators can be easily controlled by the length of the short-end stub. The filter has a compact size and good stopband rejection by employing the quarter-wavelength stepped-impedance resonators. The design procedure of this kind of filter is provided. Two filters working at 2.4 GHz are designed and fabricated to demonstrate the proposed method.

Recently researchers have great interest in using multi-core processors for applications requiring intensive parallel computing. In this paper, an approach for the implementation of hybrid parallel Gravitational Search Algorithm (GSA) and Nelder-Mead (NM) algorithm using open Multi-Processing (OPEN-MP) on multi-core processors is proposed for beam-forming applications. The proposed parallel GSA-NM algorithm is used to optimize the complex excitations, amplitudes and phases, of the adaptive array elements to synthesize the array beam-pattern. The array consists of 24-elements uniformly distributed in a circular configuration. To measure the performance of the proposed approach, the results are compared with those obtained using parallel hybrid CFO-NM, and PSO-NM Algorithms.

A method for decreasing the loss in substrate integrated waveguide (SIW) structures is introduced. In this method, the dielectric substrate is partially removed. Accordingly, dielectric loss reduction has been explicated analytically. Its equivalence to the rectangular waveguide of solid walls which is partially filled with dielectric has been identified. A novel topology for demonstrating the idea is established and a low loss three port substrate integrated waveguide power divider is presented. This SIW power divider shows lower loss than conventional SIW power dividers. Proper TRL standards are realized for removing the effect of transition and/or matching sections in measurement process. For a low-loss three-port PSIW power divider, the return loss below 10 dB and transmission coefficients between -3 dB to -3.5 dB from 8.75 GHz to 10 GHz have been achieved. The measured amplitude imbalance is less than ±0.2 dB, and the measured phase difference between <S₂₁ and <S₃₁ is about 40 in the same frequency band.

With the development of nano-optic technology, the optical nano-antenna has been widely used in the fields of novel light sources, high-sensitive biological sensors, nanometer lithography, and nano-optical imaging. The relationship between the structural parameters of the antenna and the Purcell factor is very important for engineering applications. The electric near field profile of the antenna was calculated and analyzed by using the finite-difference time-domain (FDTD) method, and the influence of the structural parameters on the Purcell factor and the electric field was thoroughly investigated. A careful comparison of bowtie antenna radiation characteristics with different structural parameters was carried out. The results show that the thickness, the length and the curvature radius have great effects on the Purcell factor and the optical antenna's electric near field. These findings are promising for improving the performance of the optical bowtie nano-antenna.

This paper presents the development of a novel‘maximum entropy'-based numerical methodology for the solution of electromagnetic problems, where the inputs and system parameters vary statistically. The application of this methodology to the problem of a plane wave impinging on an array of cylindrical conducting rods with stochastic variations in its parameters is then presented. To address this problem, a statistically significant number of replicas of this array of conductors are constructed. The current profiles in these coupled conductors are estimated by using the Method of Moments (MoM). Upon estimation of the current profiles on the conductors, the monostaticradar cross-section is estimated for each replica of the array. The probability density function isthen constructed through the estimation of a finite number of moments from the available output data subject to the constraint of maximum entropy. The methodology is very general in its scope and its application to scatterers with other geometries such as spheres, spheroids and ellipsoids as well as to other application areas would form the basis of our future work.

In this article, the parametric analysis of the slot-loaded microstrip line feed patch antenna is investigated using artificial neural network model. The bandwidths of the proposed antenna obtained at TM₀₁, TM₀₂, and TM₀₃ frequency modes are 10.2 GHz, 13.6 GHz, and 17.2 GHz, respectively. The performance of the proposed antenna is analysed using artificial neural network model. The changes obtained in bandwidth due to the position of slot length and slot width are reported. The antenna parameters such as return loss, VSWR, gain and efficiency are also calculated. The simulated results obtained with the help of IE3D simulation software are trained and tested using ANN. Theoretical results are compared with simulated and experimental ones, and they are in close agreement.

In this paper, a novel concept for ultra-wideband simultaneous switching noise (SSN) mitigation in high-speed printed circuit boards (PCBs) is proposed. Using complementary spiral resonators (CSRs) etched on only a single layer of the power plane and cascaded co-centrically around the noise port, ultra-wideband SSN suppression by 30 dB is achieved in a frequency span ranging from 340 MHz to beyond 10 GHz. By placing a slit in the co-centric rings, lower cut-off frequency is reduced to 150 MHz, keeping the rest of the structure unaltered. Finally, the power plane structure with modified complementary spiral resonators (MCSRs) is designed, fabricated, and evaluated experimentally. Measurement and simulation results are in well-agreement.

A closely spaced dual-band notched UWB MIMO antenna is proposed in this paper. A traditional semi-circular monopole with ultra-wideband operation is chosen as an element of the proposed MIMO antenna. When two of the UWB monopoles are put together closely, the mutual coupling between them is apparently strong. To reduce the coupling between the antenna elements, a T-shaped branch is inserted between them, which reduces the mutual coupling obviously over the entire operating band. Also, the T-shaped branch can perform as a compensating radiator which can lower the operating frequencies of the proposed antenna. In order to achieve dual band-notched characteristics, meandering slots are cut in the patches, and symmetrical C-shape strips are nearly placed to the monopoles' feed-lines. The meandering slot is for lower band notch (WiMAX, 3.3-3.7 GHz) while the C-shape strips are for upper band (WLAN, 5.15-5.825 GHz). The measured radiation efficiencies, peak gains and radiation patterns are illustrated and show good agreement as anticipated.

The voltage on a single-turn loop inside an enclosure characterizes the enclosure shielding effectiveness against a lightning insult. In this paper, the maximum induced voltage on a singleturn loop inside an enclosure from lightning coupling to a metal enclosure wall is expressed in terms of two multiplicative factors: (A) the normalized enclosure wall peak penetration ratio (i.e., ratio of the peak interior electric field multiplied by the sheet conductance to the exterior magnetic field) and (B) the DC voltage on an ideal optimum coupling loop assuming the ideal penetration ratio of one. As a result of the decomposition, the variation of the peak penetration ratio (A) for different coupling mechanisms is found to be small; the difference in the maximum voltage hence arises from the DC voltage on the optimum coupling loop (B). Maximum voltages on an optimum coupling loop inside a finite cylinder enclosure for direct attachment and a lightning line source at different distances from the enclosure are given in Table 3.

This paper proposes some approaches to model Ultra Wideband (UWB) antenna arrays. Based on the array factor, often stipulated as not adapted for the description of the properties of UWB arrays in the literature, an analytical expression of the beampattern is developed. The achieved results are coherent with other formulations and empiric studies proposed in the literature. Furthermore, a time-frequency modeling of UWB antenna arrays is proposed using the concept of array factor and antenna effective length.

Imaging is a valuable tool for solving inverse source problems. The achievable image quality is determined by the imaging system. Its performance can be evaluated by using the concept of point spread functions (PSFs). It is common to compute the PSFs using a numerical algorithm. However, in some cases the PSFs can be derived analytically. In this work, new analytical PSFs are presented. The results apply to scalar and dyadic scenarios in 3D originating from acoustics and electromagnetics. Data sets with narrow angular acquisition or complete spherical coverage are considered, where broadband and narrowband frequency domain data is supported. Several visualizations accompany the resulting formulas. Finally, the analytical PSFs are verified using a numerical implementation of the imaging process.

In this paper, two types of reconfigurable Dielectric Resonator Antennas (DRAs) are presented. The designs are based on rotating a Dielectric Resonator (DR), placed on the patch of the antenna, using a DC stepper motor connected to the DR to reconfigure the notch frequency, in the first, and the resonance frequency in the second design. The attained results are a UWB DRA with a reconfigurable notch in the 3.2-5.1 GHz range that prevents interference to many narrowband systems in this range, and a DRA with a reconfigurable resonance frequency suitable for microwave and WiMAX applications. The characteristics of the designed antennas are investigated using HFSS and experimentally verified. The computed and measured results are in good agreement, and the antennas meet their design criteria.

In an effort to improve the bandwidth of the single layer reflectarray, this paper investigates the use of double concentric circular ring elements arranged in a range of sub-wavelength grids on a single layer of substrate. Compared to the traditional λ/2 grid arrangements, when the radiating elements are arranged in grids less than λ/2, the reflected phase is more uniform over a wider frequency bands when radiating elements' parameters are varied; albeit with a reduced reflected phase range. The double concentric circular ring elements used here also allow an additional degree-of-freedom to improve the bandwidth. A comprehensive investigation on reflectarrays' performance with various grid spacings is conducted and the trade-off between the reflectarray gain and bandwidth is also discussed. Based on the concentric ring element, four offset-fed 0.43 m×0.43 m reflectarrays centered at 10 GHz with various element periodicities, namely λ/2, λ/3, λ/4 and λ/5 grids, are designed and developed. The measured results show that among the four reflectarrays, the one with λ/4 grid spacing achieves the broadest 2-dB gain bandwidth of 33% with an aperture efficiency of 36.2%.