A new compact and simple design of UWB antenna with triple band-notched characteristic is proposed in this paper. The first band notch for 3.3-3.8 GHz (WiMAX) is created by cutting a line slot in the radiating patch. The second band rejection for 5.1-5.8 GHz (WLAN) is achieved by etching out an elliptical split ring resonator (ESRR) from the patch placed just above the feed line and patch junction. And the third notch for 7.25 GHz-7.75 GHz (X-band satellite downlink frequency) is created using rectangular split ring resonator (RSRR) in the feed line. Each notch can be adjusted without disturbing the others. A 10 dB return loss wide bandwidth (3.1-10.6 GHz) and VSWR>2 for the stopbands has been measured.

This paper presents a microwave imaging for brain tumour detection utilizing Forward-Backward Time-Stepping (FBTS) inverse scattering technique. This technique is applied to solve electromagnetic scattered signals. It is proven that this technique is able to detect the presence of tumour in the breast. The application is now extended to brain imaging. Two types of results are presented in this paper; FBTS and FBTS integrated with image segmentation as a pre-processing step to form a focusing reconstruction. The results show that the latter technique has improved the reconstructions compared to the primary technique. Integration of the image segmentation step helps to reduce the variation of the estimated dielectric properties of the head tissues. It is also found that the optimal frequency used for microwave brain imaging is at 2 GHz and able to detect a tumour as small as 5 mm in diameter. The numerical simulations show that the integration of image segmentation with FBTS has the potential to provide useful quantitative information on the head internal composition.

The spatial resolution of an imaging system is a key factor, which steers its performance for complex target detection, characterization and recognition. Active electromagnetic imaging systems with limited frequency bandwidth and synthetic aperture may fail to discriminate important details during the imaging process, due to their insufficient resolution properties. Spectral estimation methods may be used to overcome such limitations through dedicated signal processing techniques. This study proposes a new signal processing chain, which is able to cope with near-field and wide-band configurations, to significantly improve 2-D resolution, using classical spectral estimation methods. This work is based on an efficient handling and compensation of critical signal properties, such as near-field and wide bandwidths, which make the proposed technique able to deal with very general imaging configurations, such as near/far-ranges, narrow/wide-beamwidths and -bandwidths, very short aperture... Experimental results obtained at millimeter-wave are shown to demonstrate the performance and versatility of the proposed approach.

In this paper, an efficient broadcasting technique for digital-video and audio broadcasting (DVB/DAB) is proposed using High-Altitude Platforms (HAP) and a new adaptive beamforming technique. The proposed beamforming technique uses two cascaded weighting functions to generate uniform flat footprint with improved link performance compared to terrestrial systems. These two weighting functions include flattening and smoothing coefficients to generate flat power distribution with lower sidelobe levels. Simulation results show that the generated coverage beam pattern has low sidelobe levels that is more than 40 dB below the main coverage level with less than 1 dB variation over the main coverage lobe level. Also, an almost uniform bit-energy to noise power spectral density can be achieved over the coverage area with minor variations due to the changing slant distance over the coverage area of broadcasting HAP.

Linear-to-circular polarizers operating from roughly 17 to 65 GHz, and angles of incidence up to 60° are reported. These polarizers convert incident, linearly polarized radiation into circular polarization upon transmission. First, previous designs inspired by the optics community using cascaded waveplates are scaled down to mm-wave frequencies. The naturally occurring anisotropic crystals that the optics community employed are replaced here with metamaterials. The range of incidence angles is improved by utilizing biaxial, artificial dielectrics whose permittivity in the $x$, $y$ and $z$ directions are all engineered. Next, an ultra-wideband linear-to-circular polarizer consisting of cascaded sheet impedances is reported. The cascaded sheet impedance polarizer utilizes a combination of meanderline and metallic patch geometries. The principal axes of each patterned metallic sheet are oriented at an optimized angle, which increases the design degrees of freedom and performance. This polarizer has the advantages of being thinner and easier to fabricate than the polarizer utilizing cascaded waveplates, but is more difficult to design. Both polarizers rely heavily on genetic algorithm optimization in the design process to realize multiple octaves of bandwidths and robust performance at wide angles of incidence. The polarizers are fabricated with commercial printed-circuit-boards, and then experimentally characterized.

An analytical model based on the Bethe's theory of diffraction by small holes is presented to predict the shielding effectiveness (SE) of metallic rectangular enclosure with electrically large aperture under plane wave illumination over a wide frequency range (0~3 GHz). In this model, the aperture is represented as electric and magnetic dipoles located at the center of the aperture, and the coupling relation between external plane wave and electromagnetic field inside the enclosure is established. The approximate solution of electromagnetic field distribution inside the enclosure is obtained in terms of the integrals of the electric and magnetic dynamic Green function. Finally, the influence of enclosure thickness on SE is calculated by introducing thickness attenuation coefficient. The model considers the effect of the thickness on the calculation results and is simple with low computation complex and high estimation accuracy. Besides, the effects of parameters like enclosure and aperture dimensions, aperture and observation point positions, incident and polarization direction of the plane wave on SE can be analyzed comprehensively based on the model. Simulation results of the proposed model are in accord with that of the TLM method, which verifies the accuracy and reliability of the model.

This paper describes a highly robust and efficient parallel computing method for the transient simulation of low-frequency electromagnetics with nonlinear materials and/or permanent magnets. In this method, time subdivisions are introduced to control the memory usage and nonlinear convergence. A direct block triangular matrix solver is applied to solve the formulated block matrix for each subdivision. This method has been implemented using the Message Passing Interface (MPI) for distributed memory parallel processing. Depending on the number of available MPI processes and physical memory, the entire nonlinear transient simulation can be divided into several subdivisions along the time-axis such that each MPI process handles only the computation for one time-step. Application examples are presented to demonstrate that this method can achieve excellent scalability of speedup.

There is no doubt that electrified vehicles are superseding internal combustion engine vehicles for road transportation. Among them, electric vehicles (EVs) have been identified as the greenest road transportation while hybrid EVs have been tagged as the super ultra-low emission vehicles. In this paper, the definition, classification, merits and demerits of electric and hybrid vehicles are first introduced. Then, after revealing their multidisciplinary technologies and development trends, the state-of-the-art electromagnetics research in electric and hybrid vehicles are discussed, with emphasis on electric motors for electric propulsion, electric machine systems for hybrid propulsion, wireless power transfer technologies for park-and-charge a well as move-and-charge, electromagnetic interference and compatibility issues in EVs, electromechanical flywheels for energy storage and magnetic sensors for EV operation. Meanwhile, the development trend of these research areas is revealed.

In this paper, the AC interference produced by an overhead power transmission line on a buried metallic pipeline is estimated using a circuital method based on the well-known Carson's formulae and a two-dimensional finite element numerical code. The finite element formulation used in this paper implicitly takes into account the mutual inductive coupling between all the considered conductors, and it allows a more detailed analysis in cases where a nonhomogeneous soil is present. The FEM approach includes a procedure which has been developed to enforce that the sum of the currents flowing through the soil, pipeline and eventual overhead ground wire is equal to zero. A case study has been identified, and the results obtained by the two approaches have been compared and discussed

Quantitative microwave holography is a recent imaging methodology that shows promise in medical diagnostics. It is a real-time direct inversion algorithm that reconstructs the complex permittivity from S-parameter measurements on an acquisition surface outside of the imaged object. It is recognized that this imaging method suers from limitations in tissue imaging due to a forward model which linearizes a highly nonlinear scattering problem. It is therefore important to study its limitations when reconstruction is aided by certain pre- and post-processing filters which are known to improve the image quality. The impact of ltering on the quantitative result is particularly important. In this work, the reconstruction equations of quantitative microwave holography are derived from rst principles. The implementation of two linearizations strategies, Born's approximation and Rytov's approximation, is explained in detail in the case of a scattering model formulated in terms of S-parameters. Furthermore, real-space and Fourier-space lters are developed to achieve the best performance for the given linearized model of scattering. Simulated and experimental results demonstrate the limitations of the method and the necessity of ltering. The two approximations are also compared in experimental tissue reconstructions.

This study describes the techniques and signal properties of a large, powerful, and linear-scanning 1.5 MHz induction field scanner. The mechanical system is capable of quickly reading the volume of relative large objects, e.g., a test person. The general approach mirrors Magnetic Induction Tomography (MIT), but the details differ considerably from currently-described MIT systems: the setup is asymmetrical, and it operates in gradiometric modalities, either with coaxial excitation with destructive interference or with a single excitation loop and tilted receivers. Following this approach, the primary signals were almost completely nulled, and test objects' real or imaginary imprint was obtained directly. The coaxial gradiometer appeared advantageous: exposure to strong fields was reduced due to destructive interference. Meanwhile, the signals included enhanced components at higher spatial frequencies, thereby obtaining a gradually improved capability for localization. For robust signals, the excitation field can be powered towards the rated limits of human exposure to time-varying magnetic fields. Repeated measurements assessed the important signal integrity, which is affected by the scanner´s imperfections, particularly any motions or respiratory changes in living beings during or between repeated scans. The currently achieved and overall figure of merit for artifacts was 58 dB for inanimate test objects and 44 dB for a test person. Both numbers should be understood as worst case levels: a repeated scan with intermediate breathing and drift/dislocations requires 50 seconds, whereas a single measurement (with respiratory arrest) takes only about 5 seconds.

This letter presents the synthesis of a broadband rat-race consisting of a miniaturized broadband rat-race hybrid and transmission line cascades. This broadband technique involves connecting a cascade of transmission lines with lengths equal to a quarter of the wavelength at the design frequency to each port of a previously proposed rat-race hybrid. Butterworth and Chebyshev performances of the broadband rat-race hybrid are also reported. The broadband rat-race hybrid was implemented on an FR4 substrate using spiral inductors and chip capacitors. For the frequency range of 420-800 MHz, which corresponds to a relative bandwidth of more than 62%, the broadband rat-race hybrid exhibited power splits of -3.8 ± 1.0 dB, return losses of greater than 19 dB, and isolation between output ports of greater than 20 dB. The phase difference between S₂₁ and S₄₁ was 180° ± 3°.

This paper presents a new approach for linear antenna array failure correction using geometry optimization of the failed antenna elements. It is done by changing the length and spacing of failed elements while the spacing and length of remaining elements are fixed. The flower pollination algorithm based on the characteristic of flowering plants has been used to correct the radiation pattern of linear antenna array with desired side lobe level and minimum return loss. Simulations are performed using Matlab. Two examples are given to show the effectiveness of the proposed method. In addition, the obtained results from simulation on Matlab are also validated by the results obtained from FEKO analysis.

In South East Asian countries, particularly in a developed Asian city, open-trench drains systems are prominent due to climatic differences. Open-trench drain structures occupy a great part of the terrain topography in Malaysia, and therefore this project aims to further investigate the impacts that open-trench drain systems have on radio propagation prediction in a low density urban environment. Towards that end, we have engaged an interactive 3D ray-tracing tool to build the environment depicting a low density setting with clusters of low rise building structures oriented far apart from each other. The existence of open-trench drains is incorporated into a mock city model to obtain propagation prediction results for different operating frequencies. One of the primary differences this study in comparison to the existing studies on ray-tracing modeling of an urban city with open-trench drains is that the quantity of building models and open-trench drain structures are generated over a wider area to mimic actual low dense city settings. When such scenarios are considered, the impacts of open-trench drain structures fade away.

This paper presents a study of planar silicon lens antennas with up to three steppedimpedance matching regions. The eective permittivity of the matching regions is tailor-made by etching periodic holes in the silicon substrate. The optimal thickness and permittivity of the matching regions were determined by numerical optimization to obtain the maximum wide-band aperture eciency and smallest side-lobes. We introduce a new geometry for the matching regions, referred to as shifted matching regions. The simulation results indicate that using three shifted matching regions results in twice as large aperture eciency as compared to using three conventional concentric matching regions. By increasing the number of matching regions from one to three, the band-averaged gain is increased by 0.3 dB when using concentric matching regions, and by 3.7 dB when using shifted matching regions, which illustrates the advantage of the proposed shifted matching region design.

A distortion-less ultra-wideband tapered slot antenna is designed to achieve wide band impedance matching and high gain without requiring coupling liquids. The antenna is embedded in a suitable dielectric material for compact size and performance improvement. The near-field test is simulated by placing several field probes near the antenna to plot the radiation pattern and polarization isolation. The antenna exhibits a highly directive pattern and polarization isolation in near field. The time domain antenna distortion is tested by calculating the fidelity and group delay. The results show low distortion and also show the importance of covering the antenna by dielectric layers for bandwidth increment and distortion reduction. To evaluate the antenna performance in breast cancer detection, three breast phantoms are imaged by using the raster scan imaging method. Two approaches are proposed to detect tumors without the need of breast background data. The approaches based on the effect of the tumor on transmission and reflection parameters on the frequency band allowed for medical applications. The obtained images show the antenna to be a strong candidate for breast imaging as well as in tumor detection for different scenarios that include complex multi-layer phantom and small tumor.

This paper represents the analysis and study of selecting the highest power node in the wireless sensor networks as a cluster head. The study assumes that the sensors are fixed and uniformly distributed, and the position of the sink and the dimensions of the sensor are known. The paper introduced a proposed protocol to prolong the time interval before the death of the first node (stability period), which is critical for many applications. The aim of this paper is also to improve the performance of the network by increasing the overall throughput of the network. The proposed protocol selects the cluster head depending on the power level of the node which is the most important factor of the behavior of the nodes. The simulation is made by MATLAB, and the results are compared with two other protocols, LEACH and SEP. It is found that the selection of the highest power node as a cluster head increases the stability region and throughput of the network compared to other protocols.

We propose a novel absorber by integrating four different-sized pyramidal metamaterials into a unit cell, which leads to a super broadband absorption by properly selecting the geometrical parameters for each pyramid. It is found that in such a design strategy, the high-order modes may be excited and further enhanced by multi-layer overlapping between adjacent unit cells. The as-designed MA, which consists of 13 pairs of alternating metal-dielectric layers with a total thickness of 4.13 mm, shows an absorption of above 90% in the whole frequency range of 7-21.5 GHz. The full width at half maximum is 101.8%, and the ratio of operational bandwidth to thickness achieves 7. The proposed MA is 30% broader and 5.2% thinner than previously reported absorbers working in the same spectral region. Numerical result shows that the proposed absorber is independent of the polarization. The absorption decreases with fluctuations as the incident angle increases but remains quasi-constant up to relatively large angles. Such a design shows great promise for a broad range of applications at microwave frequencies, and the proposed scheme may be extended to the visible, infrared, terahertz spectral regions.

A multiple-input-multiple-output (MIMO) antenna array with eight printed coplanar waveguide (CPW)-fed monopole antennas operating at 3.5 GHz (3.4-3.6 GHz) is presented. Each antenna is an Inverted-L (IL) monopole surrounded by a parasitic IL-shorted stripe and attains compact configuration. Both the IL-monopole and parasitic IL-shorted stripe contribute their fundamental resonant modes to operate in the desired frequency band. The neutralization line (NL) and ground middle slot are used for decoupling the antenna elements in the array. The measurement results for the prototype reasonably agree with electromagnetic simulations. Measured results for the proposed MIMO antenna array demonstrate that it has impedance bandwidth more than 200 MHz with (S₁₁ < 6 dB), and with effective antenna decoupling mechanism the mutual coupling is better than 10 dB for the required band (3.4-3.6 GHz). In addition, envelope correlation coefficient (ECC) for the proposed MIMO antenna array is less than 0.2 for any two antennas to realize independent prorogation path for a channel. The average channel capacity of the proposed MIMO antenna array is approximately 35 to 38 bps/Hz for a reference signal to noise ratio (SNR) of 20 dB.

In this article, a set of closed-form expressions is proposed to predict the resonant frequency, quality factor, input impedance, bandwidth efficiency, directivity and gain for a coax-fed electromagnetically coupled rectangular patch antenna. The computed results obtained with the present model are compared with the experimental and HFSS simulated results. The present model shows less error against the experimental and simulated results.