The diffraction by a finite sinusoidal grating is analyzed for the H-polarized plane wave incidence using the Wiener-Hopf technique combined with the perturbation method. Assuming the depth of the grating to be small compared with the wavelength and approximating the boundary condition on the grating surface, the problem is reduced to the diffraction problem involving a flat strip with a certain mixed boundary condition. Introducing the Fourier transform for the unknown scattered field and applying an approximate boundary condition together with a perturbation series expansion for the scattered field, the problem is formulated in terms of the zero-order and first-order Wiener-Hopf equations. The Wiener-Hopf equations are solved via the factorization and decomposition procedure leading to the exact and asymptotic solutions. Taking the inverse Fourier transform and applying the saddle point method, the scattered field expression is explicitly derived. Scattering characteristics of the grating are discussed in detail via numerical examples of the far field intensity.

Theory, numerical simulation, and experiment on the interaction of electromagnetic wave with suddenly created periodic plasma layers are presented. In the experiment, frequency-downshifted signals of considerably large spectral width and enhanced spectral intensity were detected. Numerical simulation of the experiment, that the plasma has a finite periodic structure and is created much faster than its decay, shows that the frequency downshifted waves have a broad power spectrum and are trapped in this plasma crystal until the plasma frequency drops to become less than the wave frequency. The spectral power increases exponentially with the frequency of the frequency downshifted wave, consistent with the experiment. The simulation reveals that wave trapping results in accumulating the frequency-downshifted waves generated in the finite transition period of plasma creation and decay. Though frequency-upshifted signals were missing in the experimental measurement, it might be attributed to the collision damping of the plasma.

The method of a T-shaped antenna loading T-shaped slots for multiple band operation is presented in this paper. Inspired by the fractal antenna, the proposed method is intended to be used for designing multiple band antennas. Through loading T-shaped slots in the terminals of a T-shaped antenna, dual or triple operating bands can be achieved. In order to validate the feasibility of this method, this type of antenna is designed and simulated. The antennas are respectively fed by two different feeding transmission lines (microstrip transmission line and coplanar waveguide (CPW) transmission line) for the purpose of identifying the method that can be commonly used. The parametric analysis in detail has been given to explain the effects of the key parameter variations. For WLAN and WiMAX applications, the antennas are fabricated and measured. Both simulated and measured results are presented to demonstrate the feasibility of these designs.

This paper presents a general method to isolate the compact dual-element antenna for mobile radio communications. The basic concept to cancel the coupling current is proposed, and two individual implemental solutions, connecting the transmission lines and the antenna elements, are illustrated respectively. Two examples targeted at 2.4 GHz ISM band have been implemented for the practical cellular phone environment. The antennas are well designed followed by the proposed principle. The result shows that the magnitude of S₂₁ between two ports can be no higher than -10 dB in the interested bandwidth after applying the proposed methods. Good agreements are observed between measurements and simulations. It is suitable for application to mobile terminals due to its relatively low profile and good MIMO performance.

The traditional coplanar electromagnetic bandgap (EBG) structure is analyzed. The method is studied to lower the center frequency and broaden the bandwidth in this paper. A novel structure of U-bridged EBG power plane is proposed. The simulation and test results show that the bandwidth of the new structure is 4.32 GHz, and the lower side cutoff frequency is at 380 MHz with stopband depth at -40 dB. The elimination of simultaneous switching noise (SSN) as this kind of U-bridged coplanar EBG structure is more effective below 1 GHz. In addition, the eye diagram of the structure is analyzed. The degradation of the maximum eye open and the maximum eye width on the structure is about 1.2% and 5.7% respectively. Finally, the IR-drop and dc resistance is accurately investigated through 3-D simulations.

The analytic expressions for the absorption coefficient (ACF) of a weak electromagnetic wave (EMW) by confined electrons in rectangular quantum wires (RQWs) in the presence of laser radiation modulated by amplitude are calculated by using the quantum kinetic equation for electrons with the electron-optical phonon scattering mechanism. Then, the analytic results are numerically calculated and discussed for GaAs/GaAsAl RQWs. The numerical results show that the ACF of a weak EMW in a RQW can have negative values, which means that in the presence of laser radiation (non-modulated or modulated by amplitude), under proper conditions, the weak EMW is increased. This is different from the similar problem in bulk semiconductors and from the case of the absence of laser radiation. The results also show that in some conditions, when laser radiation is modulated by amplitude, ability to increase a weak EMW can be enhanced in comparison with the use of non-modulated laser radiation.

In a real airborne synthetic aperture radar (SAR), its major phase errors are usually composed of two categories, such as slow-time varying phase errors (less than several cycles of change in phase during synthetic aperture time) and fast-time varying phase errors (otherwise, including wide band random) according to the motion of aircraft. If the fast errors are no more negligible compared to the slow errors, they should be estimated and then compensated accurately to obtain a well focused image. However, it is not proper to estimate all phase errors at the same time like conventional autofocus techniques because the estimation of the fast-time varying phase errors are seriously affected by blurring in image due to the slow-time varying phase errors. In this paper, we presents an accurate hybrid phase estimation technique using two independent estimation stages of sub-aperture and an iterative golden section search method, which has advantages over several existing methods, because of its better estimation accuracy and less sensitive to the quality of extracted range bins as well as requiring less computation time. The performance of our method is illustrated by simulations of point targets and an experiment with real SAR data.

Electromagnetic Interference (EMI) test is an important part for the manufacture of power electronic equipment, which helps us not only analyze the noise characteristics of the Equipment Under Test (EUT) but also design EMI filters. The previous separation method for the Common Mode (CM) and Differential Mode (DM) noise was time consuming or costly. In this paper, a novel measurement system for CM and DM conducted EMI is described showing a good performance. The system consists of two parts, part 1: getting CM noise or DM noise through a current probe; part 2: obtaining another mode noise from a software-based method. A 150w switch mode power supply is measured to verify the proposed measurement system. The noise spectra of CM and DM signal is shown, and the results obtained by software program are compared with those obtained from a current probe measurement showing a good concordance in terms of peak value.

A compact reconfigurable four-feeding microstrip antenna with polarization diversity is presented in this paper. With four triangle-shaped elements as the radiation patch, the proposed antenna can achieve good impedance match for linear polarization (LP), left hand circular polarization (LHCP) and right hand circular polarization (RHCP). A four-way power divider made by three Wilkinson power dividers and interconnected with PIN diodes is designed to feed the four elements. By controlling the states of the diodes, the antenna can produce LP, LHCP and RHCP. By using T-shaped slots on the patch and back to back geometry, a compact size of 0.6λ₀× 0.6λ₀×0.02λ₀ is achieved. The impedance bandwidth of LP is about 80 MHz (3.3%), while the usable bandwidths (overlap of impedance bandwidth and AR bandwidth) of LHCP and RHCP are about 370 MHz (15%) and 250 MHz (10%). The average gain for LP is -2.1 dBi, and that for CP is -3.3 dBi. This reconfigurable patch antenna with switchable polarization has good performance and simple structure, which can be used for 2.4 GHz wireless communication systems.

Maintaining mutual coupling suppressing structure as simple as possible is becoming attractive in the electromagnetic and antenna community. A novel parasitic patch structure that can reduce mutual coupling between cavity-backed slot antenna elements is proposed and studied. The structure consists of only a simple rectangular patch inserted between the antenna elements and it is therefore low cost and straightforward to fabricate. The proposed structure can not only suppress the surface-mode propagation and reduce mutual coupling between slot antennas, but also improve radiation patterns. The features include small occupied area and very simple structure.

An L/C dual-band dual-polarized (DBDP) shared aperture microstrip array is proposed in the paper. In the array, the sandwiched stacked patch is employed for the L-band element to exploit the bandwidth for given element thickness. Several key issues regarding the proposed structure are discussed, including: 1) benefit of proposed L band sandwiched stacked patch; 2) C-band feeding method; 3) radiation performance in both bands. A prototype array of L/C DBDP sandwiched stacked patch is designed and fabricated to verify the feasibility of the proposed structure, where the measured data are presented in the paper.

A distinctive connection method in cascaded RF/MW active device system achieving both stability and low gain loss is presented. Unlike traditional methods (isolator and attenuator), the proposed solution introduces an appropriate length of transmission line to change the input impedance at the out-band instable frequency point and uses a narrow-band termination to absorb the instable power without deteriorating in-band signal. Moreover, the reason that instability often occurs in the cascaded system is analysed with S-parameters， and it turns out to be a kind of out-band instability. And then the solution is verified by an adjustable circuit example whose insertion loss is below 0.3 dB.

A novel frequency reconfigurable 4G Multiple-Input Multiple-Output (MIMO) handset antenna is presented and verified with experimental results. Frequency tuning is used to minimize the antenna volume and to compensate for the losses related to user-originated impedance detuning. Both antenna elements are independently frequency reconfigurable and can cover most of the LTE-A bands. The study compares the losses of CMOS- and MEMS-based digitally tunable capacitors (DTC). In addition, two prototypes with total antenna volumes of 1170 and 3900 mm³ have been studied. The results show that the larger antenna structure operates with an efficiency better than 49% across the frequencies of 698-960 MHz and better than 56% across the frequencies of 1430-2690 MHz, when a MEMS-based DTC is used. In addition, a new method is introduced to estimate the suitability of the antenna geometry for frequency tunable antennas.

A capacitor-loaded coupled loop structure is investigated for wireless power transfer at 6.78 MHz for a target transmission distance of 1 m. It is shown that the optimal configuration for this structure occurs when the coupled loops are coplanar. Therefore, by converting thick wires into wide strips, a planarized configuration can be achieved. Simulation results are verified in measurement, which shows a 60% overall power transfer efficiency at 1 m. The contribution of different loss mechanisms is examined. Next, power transfer efficiency in the presence of dielectric materials is investigated in simulation and measurement. Additionally, tuning capabilities that arise from the implementation of variable capacitors are shown. Finally, design space exploration is performed to examine design tradeoffs.

This paper deals with an innovative implementation of a semi-analytical modeling method, called the Distributed Points Source Method (DPSM), in the case of an eddy current problem. The DPSM has already shown great potentialities for the versatile and computationally efficient modeling of complex electrostatic, electromagnetic or ultrasonic problems. In this paper, we report a new implementation of the DPSM, called differential DPSM, which shows interesting prospects for the modeling of complex eddy current problems such as met in the non-destructive imaging of metallic parts. In this paper, the used eddy current imaging device is firstly presented. It is composed of an eddy current (EC) inducer and a magneto optical set-up used to translate the magnetic field distribution appearing at the surface of the imaged part, into a recordable optical image. In this study, the device is implemented for the time-harmonics (900 Hz) imaging of a two-layer aluminum based assembly, featuring surface-breaking and buried defects. Then, the basics of the time-harmonics DPSM modeling are recalled, and the differential approach is presented. It is implemented for the modeling of the interactions of the eddy current imaging device with the considered flawed assembly in the same operating conditions as the experimental implementation. The comparison between experimental and computed data obtained for millimetric surface and buried defects is presented in the form of complex magnetic cartographies and Lissajous plots. The obtained results show good agreement and open the way to the modeling of complex EC problems. Furthermore, the low computational complexity of the differential DPSM modelings makes it promising to consider for the solving of EC inverse problems.

Human body communication (HBC) is a promising wireless technology that uses the human body as part of the communication channel. HBC operates in the near-field of the high frequency (HF) band and in the lower frequencies of the very high frequency (VHF) band, where the electromagnetic field has the tendency to be confined inside the human body. Electromagnetic interference poses a serious reliability issue in HBC; consequently, it has been given increasing attention in regard to adapting techniques to curtail its degrading effect. Nevertheless, there is a gap in knowledge on the mechanism of HBC interference that is prompted when the human body is exposed to electromagnetic fields as well as the effect of the human body as an antenna on HBC. This paper narrows the gap by introducing the mechanisms of HBC interference caused by electromagnetic field exposure of human body. We derived analytic expressions for induced total axial current in the body and associated fields in the vicinity of the body when an imperfectly conducting cylindrical antenna model of the human body is illuminated by a vertically polarized plane wave within the 1-200 MHz frequency range. Also, fields in the vicinity of the human body model from an on-body HBC transmitter are calculated. Furthermore, conducted electromagnetic interference on externally embedded HBC receivers is also addressed. The results show that the maximum HBC gain near 50 MHz is due to whole-body resonance, and the maximum at 80 MHz is due to the resonance of the arm. Similarly, the results also suggest that the magnitude of induced axial current in the body due to electromagnetic field exposure of human body is higher near 50 MHz.

An orthogonal beam-forming network (BFN) is proposed for 4G pattern-diversity applications. Different from the traditional Butler beam-forming networks with 2^N orthogonal beams, the orthogonal BFN, composed of three 180° hybrids and a 90° phase shifter, provides three orthogonal beams. Design procedure of the orthogonal BFN based on the factorization of its transmission matrix is derived. Moreover, in order to implement the proposed orthogonal BFN with low insertion loss, a rat-race has been used to realize unequal power distribution between its two output ports. The measured scattering parameters of the orthogonal BFN are compared with the analytical and the simulated scattering parameters, validating the expected behavior. In addition, by varying the output power ratio of the non-equi-amplitude 180° hybrid, the performance of the orthogonal BFN is improved when the proposed orthogonal BFN is used in an antenna array.

A compact microstrip-fed antenna with dual band-notched characteristics for ultrawideband (UWB) applications is presented. By introducing two open-ended inverted L-shaped slots, two sharp notches are achieved at frequencies of 3.16-3.70 GHz and 5.10-5.95 GHz for VSWR < 2. A rectangular slot in the ground plane can improve the impedance bandwidth of the proposed antenna. The prototype occupies a compact area of 22 × 26 mm². The measurement results indicate that the proposed antenna can reject the interference with coexisting worldwide interoperability for microwave access (WiMAX) and wireless local area network (WLAN) systems. The proposed antenna shows relatively omnidirectional radiation patterns in the pass band.

This study proposes a differential-fed microstrip antenna, which is characterized with an ultra-wideband of 120% (3-12 GHz), improved radiation patterns, stable gains, and compact size. Two symmetrical trapezoid shaped slots and four triangle-cut corners on the ground are used to improve the impedance matching over the UWB frequency band. To clarify the improved radiation characteristics, the simulated radiation patterns of the proposed antenna are compared with the conventional single-ended feed UWB antennas. The measured results show that, in the entire frequency band, the designed antenna exhibits a stable radiation patterns and the gain variation is less than 2 dB. Furthermore, the polarization purity are increased compared with the conventional ones, especially in the high frequency band.

Soil density is one of the important parameters to be investigated in civil, geological and agricultural works. Unfortunately, the challenging issue is found on the suitable model in determining accurately the soil density. In this article, a new soil density model based on radio-wave surface reflection method is presented. The development of the model is based on result analysis collected from the experiment. Then, comparisons with related theoretical models, Hallikainen and Topp, are performed. The experiment is performed by using a vector network analyzer (VNA) that generates radar signal and recording return loss (S₁₁) from a horn antenna. In the analysis, two new proposed soil density models have shown good agreement for soil density from 1.1 g/cm³ to 1.7 g/cm³ for sand and silty sand samples. This is verified when the model able to predict real samples as the one used in the experiment and result shows a very small relative error within 0.05% and 6.87%. Additionally, spectrograms in real time were produced in this study in order to observe more on the soil density. By using the proposed developed models, soil density estimation can be easily determined with minimal data input such as soil type, return loss and reflection coefficient by using regular radio-wave devices.