A miniaturized self-matched negative group delay (NGD) microwave circuit without the need for external matching networks is proposed. The NGD circuit is based on a modified parallel-type RLC resonator, in which lumped elements (capacitors and inductors) are implemented by microstrip gaps and high-impedance and short-circuited microstrip lines. To verify the design concept, an NGD circuit with the size of 0.21λ_g×0.29λ_g is designed and fabricated. From the measurement results, the NGD time of -5.9 ns at the center frequency of 1.532 GHz is obtained with insertion loss of less than 12.5 dB, return losses of more than 25 dB and the NGD bandwidth of 45 MHz.

In order to analyze the influence of three-phase asymmetrical operation of a generator on its stable operation, firstly, taking a 24-MW bulb turbine generator as an example, the 2-D transient electromagnetic field model is established. Through the comparison analysis of the experimental results and simulation data, the correctness of the model is verified. Secondly, the values of air gap flux density, torque and loss in different conditions are obtained by using the finite element method. The effects of asymmetric three-phase current on air gap flux density, torque and loss are determined. Thirdly, the corresponding relationships between the three-phase current unbalance degree and torque ripple, eddy current loss are established, and the variations of torque ripple and eddy current loss are given when the three-phase current unbalance degree is changed. The result shows that the asymmetry three-phase current makes the torque ripple and eddy current loss increase dramatically, which seriously threaten the safe and stable operation of the generator. Finally, the further study on the torque ripple and eddy current loss of the generator under different current distributions and the same three-phase unbalance degree identifies that the content of negative sequence current is a key factor to affect the torque ripple and eddy current loss.

A new design of wideband directional couplers using a semi-elliptical edge-coupled structure is presented. This structure consists of two semi-elliptical patches on the top layer and an elliptical defected ground plane on the bottom layer to increase the coupling coefficient and operating bandwidth. Even and odd mode analysis is performed, and sets of design graphs are formulated to facilitate the design of the coupler on substrate with dielectric constants of 2.2 and 3.38. The operating frequency and coupling are controlled by the dimensions of the elliptical patch and the size of the air gap. Compared to the conventional parallel-microstrip coupler which requires extremely narrow air gap to achieve tighter coupling factor, the semi-elliptical coupler allows for wider air gap to be used, and it reduces fabrication difficulty. Both simulation and measurement results show that the proposed design exhibits wideband characteristic with a bandwidth ratio of more than 2.4 with acoupling deviation of ±1 dB.

When deriving a range-Doppler image or a time-frequency image of a fast-maneuvering target at long range, existing range alignment methods yield poor results due to the large numbers of range profiles (RPs) and range bins that are required for this task. This paper proposes a three-step range alignment method to overcome the problems of these existing methods and to yield focused images: (1) coarse alignment using the interpolated center of mass of each RP, (2) fine alignment with an integer step using an entropy cost function, and (3) fine-tuning using particle swarm optimization. Compared to existing methods, the proposed method is computationally more efficient and provides better image focus.

In this paper, a new high performance slotted waveguide antenna incorporated with negative refractive index metamaterial structure is proposed, designed and experimentally demonstrated. The metamaterial structure is constructed from a multilayer two-directional structure of electrically split ring resonator which exhibits negative refractive index in direction of the radiated wave propagation when it is placed in front of the slotted waveguide antenna. As a result, the radiation beams of the slotted waveguide antenna are focused in both E and H planes, and hence the directivity and the gain are improved, while the beam area is reduced. The proposed antenna and the metamaterial structure operating at 10 GHz are designed, optimized and numerically simulated by using CST software. The effective parameters of the eSRR structure are extracted by Nicolson Ross Weir (NRW) algorithm from the s-parameters. For experimental verification, a proposed antenna operating at 10 GHz is fabricated using both wet etching microwave integrated circuit technique (for the metamaterial structure) and milling technique (for the slotted waveguide antenna). The measurements are carried out in an anechoic chamber. The measured results show that the E plane gain of the proposed slotted waveguide antenna is improved from 6.5 dB to 11 dB as compared to a conventional slotted waveguide antenna. Also, the E plane beamwidth is reduced from 94.1 degrees to about 50 degrees. The antenna return loss and bandwidth are slightly changed. Furthermore, the proposed antenna offers easier fabrication processes with a high gain than the horn antenna, particularly if the proposed antenna is scaled down in dimensionality to work in the THz regime.

This paper proposes an optimization method to improve the efficiency of air core inductors, which are frequently employed in near field communication, wireless power transfer, and power conversion systems. We propose a modification to the PEEC based method, which aims at further reducing the computational complexity associated with complex 3D topologies. The main idea is to optimize 3D structures based on a 2D analysis. The device low frequency behavior is estimated based on the full 3D topology, while corrections resulting from high frequency effects are estimated based on a 2D approximation. As a result, since 2D formulations are used to estimate the high frequency effects, it is possible to obtain small mesh sizes, and hence to decrease the computational load, enabling a fast iterative design process. In addition, the proposed method requires no special commercial software, and can be easily implemented in Matlab. Results are compared to a standard commercial FEM tool, CST EM studio, and the results match well.

A planar substrate integrated waveguide leaky wave antenna with cross slots is proposed in the frequency range of 10 GHz-15.5 GHz. Moreover, the symmetrical version of the structure is designed and analyzed in terms of the simulated S parameters and E field distribution which shows the existence of the open stopband in the frequency range (12.91 GHz-14 GHz), consequently degrading the radiation beam at broadside. Therefore, asymmetry is introduced in the unit cell design with respect to the position of the cross slots to achieve the continuous beam scanning in the desired frequency range. Unit cell is analyzed with the help of dispersion relation and Bloch impedance for predicting the beam scanning and matching of the proposed LWA respectively. This leaky TL is fabricated by the standard printed-circuit board process. Measured results are almost consistent with the simulation ones with a continuous beam scanning from of -40° to 16° with gain varying from 8.5 dBi to 11 dBi.

In this paper, a simple dual-band compact slotted square ring patch antenna has been used as hyperthermia applicators in the treatment of cancerous human cells at superficial depths inside the body. The proposed antenna has the advantages of dual-band (f₁=434 MHz and f₂=915 MHz) operation and more compact size (124×124 mm²) than the current state-of-the-art designs without significant frequency detuning or impedance mismatch which makes it a more suitable choice for local hyperthermia. The proposed antenna provides a suitable specific absorption rate (SAR) penetration profile and shows a good resonance at two designed frequencies. We have optimized the structure so that the SAR level performed by the structure is sufficiently enough so as to meet the IEEE standard requirements for medical applications including hyperthermia. We have simulated and measured the structure with a low-profile substrate (i.e., FR4 substrate with ε_r=4.4 and thickness of 1.6 mm). During the design process, the simplified planar tri-layered tissue model interfaced with a water bolus is used to incorporate the main electrical effects on the antenna. The results validate the proposed antenna design.

An innovative idea of shuffled structure of two quarter wavelength plates is proposed in this paper, which is supported by the numerical simulation results obtained through the application of the method of characteristics (MOC). In contrast to traditional anti-reflective coatings techniques, the proposed structure is a shuffled arrangement of two quarter wavelength slabs which are in theory evenly divided into N+1 and N pieces and then stacked up alternatively. These slabs are made of non-magnetic (μ_r = 1) dielectric (ε_r > 1) materials respectively characterized by dielectric constants ε_r1 and ε_r2 having the relation of ε_r2 =(ε_r1)² to allow maximum transmission. These 2N+1 pieces are assembled such that there is always an ε_r2 piece between two ε_r1 pieces. Therefore, the proposed structure has the advantages of simple components and easy assembly. In the present simulation, the integer number N ranges from one to ten. The computational results are demonstrated in both time and frequency domains exhibiting that the proposed structure functions as a frequency selector.

Statistical moments of a scattered field are calculated in the first and second approximations using modified smooth perturbation method. Analytical expressions of both the variance and correlation function are obtained in the principle plane containing wave vector of an incident wave and external magnetic field. Observation points are spaced apart at small distances taking into account diffraction effects. Numerical calculations are carried out for the anisotropic Gaussian spectral function containing both anisotropic factor and the angle of inclination of elongated anisotropic plasma irregularities using the experimental data. It was shown that 3D surface of the correlation function of the phase fluctuation oscillate and these variations are decreased increasing characteristic spatial scale of plasma irregularities. New peculiarities of the ``Double-humped Effect'' are revealed in the collisionless magnetized plasma. It was shown that spatial scale and the inclination angle of elongated anisotropic plasma irregularities play important role in formation of a gap in the spatial power spectrum. Varying the magneto-ionospheric plasma parameters and values of characteristic spatial scales of anisotropic irregularities the depth of a dip increases and oscillates.

A novel artificial magnetic conductor (AMC) structure for realizing gain enhancement of a double-T monopole antenna for 2.4/5.6 GHz dual-band WLAN operation is presented. First, an initial AMC unit cell is proposed, and a 2x5 array of this unit cell is placed behind a double-T monopole antenna as a ground plane, then the AMC structure is modified and improved to achieve better performance. Briefly, more than 4 dB gain improvement and other desirable characteristics including suitable radiation patterns and adequate bandwidths are reported from the simulation results of the final designed structure, and the simulation is performed by CST MWS 2014 in any of the mentioned frequencies. Finally, the validity and applicability of this design are demonstrated through experimental results of the fabricated antenna.

Wideband collocated antennas for multiple input multiple output (MIMO) systems are proposed. The structure is disposed on two substrate layers. On the first top substrate, a disc monopole is etched. The top of the second substrate contains a tapered slot antenna in a form of a Vivaldi antenna and two reflector elements in the form of half disc. The designed antenna can switch among five radiation patterns which radiate in different directions of space with only two excitation ports. All antennas have a relative bandwidth at least 23%. The antenna elements exhibit a low mutual coupling since they are around -17 dB over the considered bandwidths. This performance is believed because the disc monopole mainly has a broadside radiation while the Vivaldi antenna radiates in end-fire directions. With an overall length of about a half guided wavelength, the proposed structure is believed suitable for applications needing radiation pattern diversity.

A nonlinear metamaterial composite structure with tunable tunneling frequency is presented. Based on theoretical calculation results, a nonlinear metamaterial sandwich structure constructed by epsilon negative metamaterial (ENM), mu negative metamaterial (MNM) and nonlinear double negative metamaterial (NDNM) is designed, and its nonlinear properties are investigated. The measured results show that the tunneling frequency of the sandwich structure ENM-NDNM-MNM can be controlled conveniently by signal power.

In scattering experiments, incident fields are usually produced by aperture antennas or lasers. Nevertheless, incident plane waves are usually preferred to simplify theoretical analysis. The aim of this paper is the analysis of the electromagnetic scattering from a perfectly electrically conducting polygonal cross-section cylinder when a Gaussian beam impinges upon it. Assuming TM/TE incidence with respect to the cylinder axis, the problem is formulated as electric/magnetic field integral equation in the spectral domain, respectively. The Method of analytical preconditioning is applied in order to guarantee the convergence of the discretization scheme. Moreover, fast convergence is achieved in terms of both computation time and storage requirements by choosing expansion functions reconstructing the behaviour of the fields on the wedges with a closed-form spectral domain counterpart and by means of an analytical asymptotic acceleration technique.

Metasurfaces, due to its designable surface electric and magnetic impedances, have largely enhanced electromagnetic wave manipulation techniques. The conventional approach to realize the surface magnetic impedance requires non-planar structures, such as metallic loops, which is not easy to fabricate, especially at optical frequencies. In this work, we theoretically and rigorously prove that eective surface magnetic and electric impedances can be obtained using parallel electric metasurfaces. A synthesis method is presented which allows independent designs of surface electric and magnetic impedances. Finally, a polarization converter with high energy efficiency is designed using the proposed impedance synthesis method for verification. The proposed synthesis method is favorable for reducing fabrication complexities.

Analytical expressions that include arbitrarily directed fields on all laminate boundaries can be used for calculation of the fields inside the laminate when the boundary fields are known from, e.g., measurements. A linear laminate block could be used in non-destructive testing for comparisons between different laminates. This article contains derivation of Fourier series of harmonically time varying, traveling electromagnetic fields in homogeneous, anisotropic approximations of laminates. The component of the magnetic field strength in the stacking direction is used as a source term in twodimensional Poisson equations for the magnetic field strength in other directions. This approximation is here used in three dimensions under the precondition that the conductivity is much smaller in the laminate stacking direction than in the other directions. Sine interpolation and different choices of types of boundary conditions are discussed. Different alternative subdivisions of the Poisson boundary value problems are treated. Shorted derivations of simple analytical expressions are given for both traveling and standing waves in two dimensions. Results from Fourier series in the three-dimensional case are compared with results from finite element calculations.

An intentional focusing of High-Power Microwave (HPM) energy on microelectronic systems can produce effects that will potentially upset or damage the target. However, the physical mechanisms at work within the device are not often well understood. We provide a detailed understanding of the physical mechanisms involved in a common-source Metal Oxide Semiconductor (MOS) transistor inverter when Pulsed Microwave Excitation (PME) in a frequency range from 10 MHz to 1 GHz is applied on the gate terminal. Our study is based on the measurements of the current waveforms on all transistor access and explains the MOS response with and without the Radio-Frequency (RF) interference.

A compact triple-band monopole antenna covering WLAN/WiMAX bands is investigated in this Paper. The proposed antenna has a compact size of 36 x 25 mm² and consists of a circular ring, a split ring radiator and a trapezoid coplanar waveguide-fed structure. The antenna covers three distinct bands of 2.27-2.55 GHz, 3.23-4.14 GHz, and 5.08-6.03 GHz for WLAN and WiMAX applications. To validate the proposed design, prototype is fabricated, and measurement is carried out. Good performances of gain, radiation pattern and efficiency have also been obtained.

For the purpose of two-dimensional (2-D) imaging in the Terahertz (THz) near field through 2-D synthetic aperture radar technology, Fourier transform (FT) is one of the most popular imaging ways. However, FT-based algorithms would encounter performance loss either when spatial sampling is under Nyquist frequency or there are off-grid scatterers in the scene of interest. Therefore, by exploiting the theory of matrix enhancement and continuous parameter estimation, we propose to use matrix enhancement and matrix pencil (MEMP) method and matched filter to deal with arbitrarily located scatterers when spatial under-sampling is adopted. Through constructing a specifically expanded matrix, the information of the scatterers involved in the small data set can be enhanced. Then, highresolution grid-independence 2-D imaging can be achieved by the combination of MP and matched filter. Simulation results verify the effectiveness of the proposed algorithm.

Influence of surface impedance on radiation fields of spherical antennas excited by radially oriented electric dipole is investigated by using a Green's function for a space outside a spherical scatterer. This approach allows us to obtain analytical expressions for radiation fields of an impedance spherical antenna in the wave zone. The spherical antenna with the scatterer coated with a metamaterial layer is also considered. The surface impedance required for radiomasking of the spherical scatterer of resonant dimensions was estimated by mathematical modeling.