In this paper, an efficient time domain simulation algorithm is proposed to analyze the electromagnetic scattering and radiation problems. The algorithm is based on discontinuous Galerkin time domain (DGTD) method and parallelization acceleration technique using the graphics processing units (GPU), which offers the capability for accelerating the computational electromagnetics analyses. The bottlenecks using the GPU DGTD acceleration for electromagnetic analyses are investigated, and potential strategies to alleviate the bottlenecks are proposed. We first discuss the efficient parallelization strategies handling the local-element differentiation, surface integrals, RK time-integration assembly on the GPU platforms, and then, we explore how to implement the DGTD method on the Compute Unified Device Architecture (CUDA). The accuracy and performance of the DGTD method are analyzed through illustrated benchmarks. We demonstrate that the DGTD method is better suitable for GPUs to achieve significant speedup improvement over modern multi-core CPUs.

This paper presents a Complementary Split Ring Loaded Resonator (CLSRR) based compact, wideband, waveguide bandpass filter. Three identical CLSRRs were fabricated and placed on the transverse plane of a standard WR-90 waveguide at a quarter wavelength distance to form the filter. The proposed filter was initially simulated using Ansoft HFSS (version 14) and then fabricated and measured. The measured result shows a fractional bandwidth of 18.80% at 10.05 GHz. Total length of the filter is only 20.33 mm which is compact enough. Detailed design procedure has been presented along with the equivalent circuit of the filter. A table has been provided to compare the performance of the proposed filter with those already available in the literatures. The table shows that the proposed filter is compact and has higher bandwidth, lower insertion loss and higher return loss.

A conformal patch array antenna with omnidirectional pattern in the azimuth plane at S-band is presented. A theoretical study of the generated ripple in the omnidirectional radiation pattern according to the number of faces that conform the array has been computed. A six-faced regular prism 3D structure has been chosen following a maximum 3 dB ripple criteria in the omnidirectional radiation pattern. A rectangular microstrip patch fed by a microstrip line has been designed as single radiating element. An equal power divider has been designed as feeding network in microstrip technology to feed each radiating element. Several prototypes have been manufactured and measured to validate the theoretical and simulated results. The entire conformal array has been assembled on a hexagonal regular prism manufactured in PolyLactic Acid (PLA) material using a 3D printer. In spite of the complexity of the proposed antenna structure, the used manufacturing processes, such as microstrip and 3D printing, allows to perform a low cost, low weight and compact final antenna. A higher radiated field ripple than the expected one is generated due to small deviations between experimental and theoretical critical parameters such as the feeding network performance or the 3 dB beam-width of the single element radiation pattern. A maximum ripple value of 4 dB has been experimentally obtained in the omnidirectional radiating pattern.

A symmetrical open-circuited λ/4 trans-directional (TRD) coupled line is proposed to replace the 3λ/4 reference line of an existing 90° Schiffman phase shifter for miniaturization. The coupling factor of the TRD coupled line can be used to control input matching and phase ripple, which adds an additional optimization variable to the design of a Schiffman phase shifter. There are two transmission zeros near the operational frequency band, which can be used to suppress adjacent frequency interferences and accompanies two phase leaps so that the realizable bandwidth is about 28~42%. Simulated and measured results are given to verify the proposed method.

Statistical moments of the spatial power spectrum of multiple scattered ordinary and extraordinary waves in the turbulent collision magnetized plasma with aligned anisotropic electron density irregularities are investigated using modify smooth perturbation method taking into account diffraction effects. Correlation function and variances of the phase fluctuations are obtained for arbitrary correlation function of the electron density fluctuations. ``Double-humped Effect'' is investigated analytically and numerically using the anisotropic Gaussian spectral function of electron density irregularities for the polar ionospheric F-region applying the experimental data.

Compared with the backscattering configuration, the bistatic scattering echoes can provide multidimensional information on land surface. Based on the Michigan Microwave Canopy Scattering (MIMICS) model, a first-order microwave bistatic scattering model for vegetations is developed in this paper. The dominant scattering mechanism for wheat and soybean in the L and C bands is analyzed by simulating the bistatic scattering echoes in multiple viewpoints, which can help us understand the interaction between incident wave and vegetation parameters. The influence of crop height, leaf size and moisture of vegetations and down layer soil on the scattering echoes is fully investigated. The simulations show that the bistatic scattering echoes are more sensitive to the vegetation parameters than that in backscattering configuration. There exist optimal scattering angles, in specular direction and in direction perpendicular to the incident plane, to improve the retrieval accuracy of vegetation parameters and moisture of soil surface. Moreover, the simulations demonstrate that bistatic scattering echoes in high frequency (C band) are a good choice to retrieve the vegetation parameters, and the echoes in low frequency (L band) are preferred to retrieve the soil parameters. This research can be used to provide reference for crop monitoring and future bistatic system design.

This paper presents a high-gain cavity resonant antenna (CRA), consisting of an FSS layer placed above an aperture coupled microstrip patch antenna (ACMPA). Geometry of the proposed FSS superstrate is highly reflective with |Γ>0.9|. Ray-tracing method has been employed for determining the resonant condition of the antenna. ACMPA operating at S-band is serving as a feeding source. The coupling aperture of the antenna is of novel design, and several figures of merit have been presented for the proposed coupling aperture. Analysis of CRA has been carried out with the design parameters of the CRA. HFSS-13 has been utilized as simulation tool. Measured results are in good agreement with the simulated ones.

Magnetodielectric substrate gives a new dimension for reducing the size of the planar antennas. In this article, the patch size is reduced by taking a substrate with nano-sized nickel ferrite inclusions in LDPE polymer matrix. The antenna is made to operate in X- and Ku-bands by engraving T slots along the resonant length of the patch. Structural modification of the substrate geometry as a step profile is incorporated along the slotted patch edges to enhance performance. The T-slots, on both the radiating edges with the magnetodielectric stepped substrate show four resonant frequencies in both the X- and Ku-bands with S₁₁ < -15 dB and a maximum -10 dB bandwidth of 22.4%. A miniaturization factor of 2.97 is obtained.

The bandwidth of artificial magnetic conductor structures based on the square patch geometry has been significantly increased by using composite ferrite particles. These magnetic composites are non-conducting materials which achieve extraordinarily high values of magnetic permeability in the VHF and UHF range. Two AMC designs are presented for two different bands: the lower VHF and the VHF/UHF bands. To realize the ultra-high bandwidth for those ranges two particular materials were considered; nickel zinc and bismuth strontium titanate based ferrites. The AMCs were designed and modeled via numerical simulations using real material parameters as reported in literature. A cross-dipole radiator was integrated with the AMC to create a wideband directive antenna for SATCOM applications.

The principal purpose of this work is the simulation of the ship wake in Synthetic Aperture Radar (SAR) imaging based on a facet scattering model. The hydrodynamic model of the surface waves mainly considers the Kelvin wake waves and the wind driven waves. For the prediction of radar returns from the composite surface, the semi-deterministic facet scattering model (SDFSM) is proposed, which is verified to have good performance through a comparison with the experiment by SASS-II. Then, the distributions of backscattering normalized radar cross section (NRCS) of facets are investigated for both VV and HH polarizations and characteristics of the wake pattern are shown with good visibility. On the basis of these, an application of velocity bunching (VB) imaging model is presented in detail for the simulation of SAR imaging of sea surface waves with Kelvin wake. Finally, several numerical results provide states of the effects of ship speed, wind speed and the ship sailing direction on the characteristics of Kelvin wake in SAR images. Thus, this simulation may enable us to provide a theoretical basis to the detection of ship wakes.

Recently, researchers were interested in neural algorithms for optimization problems for several communication systems. This paper shows a novel algorithm based on neural technique presented to enhance the performance analysis of beam-forming in smart antenna technology using N elements for Uniform Circular Array (UCA) and Concentric Circular Array (CCA) geometries. To demonstrate the effectiveness and reliability of the proposed approach, simulation results are carried out in MATLAB. The radiators are considered isotropic, and hence mutual coupling effects are ignored. The proposed array shows a considerable improvement against the existing structures in terms of 3-D scanning, size, directivity, HPBW and SLL reduction. The results show that multilayer feed-forward neural networks are robust and can solve complex antenna problems. However, artificial neural network (ANN) is able to generate very fast the results of synthesis by using generalization with early stopping method. Important gain in the running time and memory used is obtained using this latter method for improving generalization (called early stopping). To validate this work, several examples are shown.

A slim tri-port antenna with polarization diversity and pattern diversity characteristics is presented for 2.45 GHz WLAN router applications. By compositing a J-pole antenna and two perpendicularly crossed dipoles, the proposed antenna achieves available vertical and horizontal polarizations covering the whole horizontal plane. Besides, the two crossed dipoles generate two orthogonal radiation patterns, making it an attractive solution for pattern diversity applications. The three antennas are integrated by sharing the bottom structure of J-pole antenna and the top structure of dipoles, resulting in a slim and compact structure. The proposed antenna is made by copper, with overall volume of only 25.5×25.5×126.5 mm³. Measure results show that return losses of three ports are all better than 10 dB and isolations between each two ports are better than 20 dB from 2.39 GHz to 2.49 GHz. Besides, simple structure, slim size, and light weight make it easy to install vertically on the WLAN routers.

A modified technique to design directional ultra-wideband (UWB) antenna with slotted ground structure approach on the ground plane has been presented for applications in C- and X-bands. Initially, elliptical slot is inserted into ground and thereafter, the axis of ellipse is rotated 45 degrees in direction of the substrate. Minor axis of the ellipse is optimized to locate it symmetrically around the circular patch in order to obtain the full C- and X-band operations and also to enhance directivity. Thereafter, for further improvement in the directivity as well as gain, an elliptical slot in circular patch has also been introduced. The impedance bandwidth approximates about 95% covering the frequency ranging from 4.18-11.50 GHz. The return losses (S₁₁) are -38 dB and -43 dB through simulation, which are -24 dB and -32 dB by measurement at 6.3 GHz, 9.3 GHz resonant frequencies, respectively. Simulated gain and half power beam width (HPBW) are 2.5-8.4 dB and 49-22 degrees in 4.18-11.50 GHz band, respectively. Gain and half power beam width (HPBW) of the proposed antenna improves by 1-2 dB and 5-10 degrees, respectively compared with previously designed antennas. Simulation of the antenna has been carried out on Computer Simulation Technology (CST) software on an FR-4 substrate having dielectric constant 4.3 of thickness 1.6 mm. The measured results show good agreement with equivalent circuit model and CST simulation.

Gain reduction on measurement of distance and on sizes of test and probe antennas are discussed. We consider only the case of linear antenna with uniform field distribution. The analysis is based on time-domain (TD) physical optics (PO) method of field calculation [1]. We show that in determining the level of the side lobe there are two competing effects: (i) the decrease in the amplitude of the signal in the direction of the side lobe and (ii) reducing the maximum signal level in the direction of zero-angle. We show the optimal measurement distance with respect to the acceptable small errors of antenna gain. It is shown that optimal relation β=b/a is about ~0.4 (a and b are the sizes of the antenna under test and the probe antenna). For this optimal relation, the well-known far-field distance criterion R₀=2D²/λ can be reduced by 2 times (D is the diameters of the antenna under test and λ is wavelength). Note that when b is optimal, the errors in determining of the sidelobe levels are also small and do not exceed 0.5 dB.

A circular sector patch antenna loaded with a periodic metamaterial topology is presented. Several shapes of the circular sector patch are analyzed, and the input impedances and radiation patterns are compared. The topology reveals a nearly constant resonant frequency at zeroth-order resonance (ZOR) while the radiation performance approaches the one of the ZOR full circular patch antenna. Compared with rectangular and circular patch antennas, the sector patch offers more tuning possibilities. A matching network can be easily introduced to enhance the impedance bandwidth. Apart from the ZOR characteristics, this topology can also support a quasi-monopolar pattern at multiple modes. A semicircular patch operating at 4.1 GHz together with an impedance matching network and a dual-band semicircular patch antenna are fabricated and measured.

A novel miniaturized single-feed cross-aperture coupled circularly polarized (CP) microstrip patch antenna loaded by four identical shorting strips is proposed and discussed. Each shorting strip underneath the edges of the radiating patch is connected to the ground plane via an array of three identical and equidistant shorting pins. With the assistance of the capacitance offered by the radiating patch and the shorting strips, and the inductance induced by the shorting pins, the patch size and overall size of the proposed antenna have been significantly reduced by 75% and 69%, respectively, compared with the conventional antenna. An antenna prototype with an overall size of 50 mm×50 mm×7.548 mm (0.317λ₀×0.317λ₀×0.048λ₀) and a patch size of 29.43 mm×27.85 mm (0.186λ₀×0.176λ₀) has been fabricated and measured, which shows a measured 10-dB return loss bandwidth of 92 MHz (4.76%) from 1.886 to 1.978 GHz with a maximum right-handed CP (RHCP) gain of 4.9 dBic. The measured 3-dB axial ratio (AR) bandwidth is 28 MHz (1.46%) from 1.899 to 1.927 GHz with a 3-dB AR beamwidth of more than 140º across the operating bandwidth.

A dual-polarized active frequency selective surface (AFSS) with switch function at LTE-D band is proposed in this paper. Double coupled metallic meandered structures on a one-layer substrate loaded PIN diodes are designed carefully to realize the band-pass characteristic at 2.6 GHz when PINs are OFF and the rejection characteristic when PINs are ON. The proposed model requires no additional biasing lines, and the amount of PINs is acceptable and affordable, which contribute to the simplicity and practicality of this AFSS in real applications. A simple equivalent circuit model (ECM) is given to better understand the design. Through full-wave simulation results, the polarization characteristics under TE and TM are almost the same, and the angle-stability stays well till 45˚. For necessary verification, one finite FSS prototype was fabricated, which was changed to one switchable AFSS by welding PINs and external feeder lines. The measured results of transmission coefficient are obtained by free space test method in the microwave anechoic chamber and agree well with the simulated ones.

The topology of grounding grid is important for diagnosing its status, which plays a critical role in the safety of personnel and stable operation of power system. The electromagnetic field method and derivative of surface magnetic flux density on the line has been used to measure the branch position in case the grid is parallel to the plane of earth surface that in practice is unknown while the node points and connections were not discussed. This paper introduces a method that uses derivative of surface flux density on circles and lines in a systematic order to find the position of the grid in the plane of the earth surface and connecting the nodes to measure the full topology. This method even identifies any angled branch present in the mesh of a grid. Software simulations and experimental tests verify that the method is feasible and can be applied to identify the topology of a grounding grid.

An experimental setup and data reduction method has been developed for noninvasive high frequency electromagnetic impedance measurements of carbon nanotube (CNT)/epoxy nanocomposites. Using time domain reflectometry and parallel plate transmission lines, dielectric properties can be measured with the specimen under tensile loading. Good dispersion and addition of CNTs lead to an increase in high frequency dielectric constant of the nanocomposites. A strong strain dependence of the impedance is observed for the well dispersed nanocomposite while the baseline epoxy showed no strain dependence. A mechanism, based on an increase in CNT-CNT tunneling capacitance with applied tensile strain has been suggested. This research is expected to introduce a noninvasive characterization technique for studying electromagnetic properties of conductive nanocomposites.

In this paper a new method to solve the microwave matching problem of MEMS shunt connected switches is proposed, as an extension of a previously presented approach based on the image parameter formulation. The image phase concept is used to impose the matching condition in the ``on'' state of the device, which is the most critical one. Two different configurations are investigated: a single basic cell and double basic cell topologies. For both of them an analytic modeling procedure is developed, and the equations for the synthesis of the structures are derived. In order to provide some examples, the method has been applied to a previously realized MEMS shunt variable capacitor.