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%.

The aim of this paper is to present a frequency domain method for synthetic aperture radar (SAR) imaging. By using two consecutive linear mappings along Doppler and frequency domains, an azimuth-dependent SAR transfer function has been discovered. Based on this new transfer function, the SAR image can be reconstructed by the proposed azimuth stacking algorithm. The new algorithm can form SAR image at each azimuth position without DFT wrap around errors. If Chirp z-transform (CZT) is applied to carry out the two consecutive mappings (since they are linear mappings), the proposed algorithm will not require interpolations and thus its reconstructed image would be free of truncation errors. The new algorithm has been validated using both simulated and experimental ultrawideband/widebeam (UWB/WB) SAR data.

We design, characterize, and analyze a new kind of metamaterial (MTM) absorber (MA) in different frequency regions for the solar cell applications. This MTM based structure is particularly presented in a range of the solar spectrum in order to utilize the solar energy effectively. The proposed MTM based solar cell provides perfect absorption for both infrared and visible frequency ranges and can be used for the realization of more efficient new solar cells. The structure is also tested in terms of the polarization angle independency. The suggested MA has a simple configuration which introduces flexibility to adjust its MTM properties to be used in solar cells and can easily be re-scaled for other frequency ranges. Our experimental results in microwave frequencies confirm the perfect absorption for the resonance frequency and agree with the simulation results. This means that the developed MA for solar cells will offer perfect absorption in infrared and even in visible frequencies.

This paper presents a unified analysis of the three-parameter aperture distributions for both sum and difference antenna patterns, suitable for communications or telemetry applications with either a stationary or tracking antenna, and with the parameters automatically determined by Particle-Swarm Optimization (PSO). These distributions can be created, for example, by reflector, phased array, or other antenna systems. The optimizations involve multiple objectives, for which Pareto efficiency concepts apply, and are accelerated by compact, analytical closed-form equations for key metrics of the distributions, including the far-field radiation pattern and detection slope of the difference pattern. The limiting cases of the threeparameter distributions are discussed and shown to generalize other distributions in the literature. A derivation of the generalized vector far fields provides the background for the distribution study and helps clarify the definition of cross-polarization in the far-field. Examples are given to show that the three-parameter (3P) distributions meet a range of system-level constraints for various applications, including a sidelobe mask for satellite ground stations and maximizing pointing error detection sensitivity while minimizing clutter from sidelobes for tracking applications. The equations for the relative angle sensitivity for the difference pattern are derived. A study of the sensitivity of the 3P parameter values is presented.

A new spiral antenna is proposed in this paper. The developed antenna has improved axial ratio (AR) and shorted arm length. The function of the new spiral is given. The developed spiral antenna combines the low frequency property of power spiral antenna and high frequency property of Archimedean spiral antenna. That is, the growth rate of radial distance at large winding angle is close to power spiral for improved AR in low frequencies, and the growth rate at small winding angle is close to Archimedean spiral for good AR in high frequencies. The results reveal that the developed spiral antenna has noticeable improved axial ratio at low frequencies compared with Archimedean spiral antenna, and the problem of axial ratio degradation of power spiral antenna was also solved. The arm length is shorted by 46.2% compared to conventional Archimedean spiral antenna, and 63.5% compared to power spiral antenna.

A polarimetric radar system measures the complete scattering matrix of a target in the backscattered field that includes magnitudes of linearly polarized scattering amplitudes and the co-polarised and cross-polarised phase angles. Apart from backscattering intensity, the co-polarization phase difference (CPD) calculated from polarimetric synthetic aperture radar (SAR) data produces important information about target physical, geometrical and dielectric properties. In the present work, the distribution of CPD in C-band polarimetric SAR data corresponding to major kharif and rabi crops (denoting the monsoon and the winter season) and other land cover features have been studied over Central State Farm, Hisar, Haryana. The probability density functions (PDF) of CPD have been compared with dominant scattering contributions from these targets as obtained from polarimetric target decompositions. The results show that crops and other land cover features show characteristic CPD distributions, which relates well with crop physical and geometrical properties. An intuition of the rate of growth and plant vigour is indicative from the temporal PDF pattern.

In this paper, a dual-band high-gain antenna based on the split ring resonators (SRRs) and corrugated plate is presented. By combining the SRRs and corrugated plate, the presented antenna resonating at different frequencies with high performance is easily achieved based on the superposition of the electric fields radiated by the SRRs and the grooves. Both the simulated and measured results show that the gain is improved by 6 dB at 12.7 GHz and 6.5 dB at 14.2 GHz respectively compared with the conventional flat antenna without grooves. Moreover, half-power beam width (HPBW) of E-plane is reduced by more than 100 degrees at 12.7 GHz and 14.2 GHz.

In this paper, a simulation of ground penetrating radar ``GPR'' system on lossy and dispersive soil is investigated. The capability of the GPR system to detect buried targets is examined by evaluating and comparing the electromagnetic coupling between the transmitting and receiving antennas in two cases: (i) when the system is placed over an empty ground and(ii) when it is placed over a ground inside which a practical target is buried at a proper depth. Simulation software based on the finite difference time domain ``XFDTD'' is used for the electromagnetic simulations. The results concerning the coupling between the transmitting and receiving antennas are presented considering various practical parameters such as the operating frequency, the electric properties of the ground soil and the buried target, and the location at which the receiving element is placed. It is shown that the target detectability is strongly dependent on all of the above parameters. Also, the capability of target shape extraction and recognition are demonstrated through polarimetric ground penetrating radar.

In this article, a compact tri-band microstrip bandpass filter (BPF) using asymmetric stepped-impedance resonators (SIRs) is proposed. Only one set of asymmetric SIRs are used in designing this filter to achieve triple passband response with high selectivity and band-to-band isolation level. By properly selecting the impedance and electrical length ratios of the asymmetric SIRs, the tri-band BPF is designed. By using a cross-coupled configuration and 0˚ feed structure, high selectivity frequency responses with six transmission zeros are achieved. The three bands of the proposed tri-band filter are located at 1.57/3.9/7 GHz, respectively, and the circuit size is much smaller in comparison with previous works using the same substrate. Measured results are in good agreement with electromagnetic (EM) simulation.