In order to design high current devices, there are many factors to be considered namely the compatibility of these devices with the internal and external propagation as well as ensuring the generation of low-frequency and high-frequency disturbances within electromagnetic environments. This contribution reports the simulation and measurement results of the electromagnetic interference (EMI) due to the fields inside and outside a Current Injection Transformer (CIT) and its control system during short circuit tests. This paper will also push the state of the art by proposing a synthetic algorithm based on a channel coding technique for error free EMI shielding to increase the performance level of the CIT against the unpredictable events or probable transient states accompanying EMI which may result in malfunctioning of the control system and data exchanges through the connectors.
Here a photonic crystal plate polarizer (with periodic air gaps), operating over a broad wavelength range extending from 1000nm to 1770nm and with a wide angular field of 16o measured in air, is suggested. The polarizer has an average degree of polarization equal to 0.9999, and a high extinction ratio (>8.308×104) in transmitted light. Since the plate polarizer does not require optical cements, it is most suitable for use with high power laser systems. It is also smaller in size as compared with multilayered cube polarizers.
This paper presents the exact analytical formulation of the three components of the magnetic field created by a radially magnetized tile permanent magnet. These expressions take both the magnetic pole surface densities and the magnetic pole volume density into account. So, this means that the tile magnet curvature is completely taken into account. Moreover, the magnetic field can be calculated exactly in any point of the space, should it be outside the tile magnet or inside it. Consequently, we have obtained an accurate 3D magnetic field as no simplifying assumptions have been used for calculating these three magnetic components. Thus, this result is really interesting. Furthermore, the azimuthal component of the field can be determined without any special functions. In consequence, its computational cost is very low which is useful for optimization purposes. Besides, all the other expressions obtained are based on elliptic functions or special functions whose numerical calculation is fast and robust and this allows us to realize parametric studies easily. Eventually, we show the interest of this formulation by applying it to one example: the calculation and the optimization of alternate magnetization magnet devices. Such devices are commonly used in various application fields: sensors, motors, couplings, etc. The point is that the total field is calculated by using the superposition theorem and summing the contribution to the field of each tile magnet in any point of the space. This approach is a good alternative to a finite element method because the calculation of the magnetic field is done without any simplifying assumption.
This paper presents a printed slot antenna using the printed structure in order to improve its dual-band and compact size performances. The printed slot structure is used as additional resonators to produce dual-band operation for covering the worldwide interoperability for microwave access (WiMAX) and the 5.2-GHz wireless local area network (WLAN) bands. In order to achieve wideband and multi-band operation, the slot antennas with a slotted structure and an inverted-L slot structure for covering the wireless communication operations are developed. Finally, we propose a novel and compact printed slot antenna with mixing slot structures to obtain and cover for the 2.4-GHz WLAN (2.4--2.484 GHz), the WiMAX (IEEE 802.16e in the Taiwan: 2.5--2.69/3.5--3.65 GHz), and the 5-GHz WLAN (5.15--5.35/5.725--5.825 GHz). Several properties of the proposed antennas for dual- and multi-band characterize radiation performances such as impedance bandwidth and radiation pattern. Measured gain has been confirmed experimentally for the multi-band wireless communication systems.
A 35 GHz alternating current (AC) direct detection receiver for passive imaging has been studied and presented. The Monolithic Microwave Integrated Circuits (MMIC) Low Noise Amplifiers (LNAs) with high gain and wide band are cascaded to provide enough gain for high sensitivity in the receiver. On basic of discussing the structure and mechanical chopping modulation, the signal model and compensation mechanism is emphatically analyzed. Finally, the imaging result is given.
A new set of higher order hierarchical basis functions based on curvilinear triangular patch is proposed for expansion of the current in electrical field integral equations (EFIE) solved by method of moments (MoM). The multilevel fast multipole method (MLFMM) is used to accelerate matrix-vector product. An improved sparse approximate inverse (SAI) preconditioner in the higher order hierarchical MLFMM context is constructed based on the near-field matrix of the EFIE. The quality of the SAI preconditioner can be greatly improved by use of information from higher order hierarchical MLFMM implementation. Numerical experiments with a few electromagnetic scattering problems for open structures are given to show the validity and efficiency of the proposed SAI preconditioner.
This paper presents a closed form solution for the electrical potential perturbation of a perfectly insulating flat circular disc embedded in a homogeneous half-space in a uniform primary electric field. It is an adaptation of Weber's method for the potential around a charged conducting disk. It yields closed form analytic solutions for the electric and magnetic fields and, by straightforward numerical integration, an easily evaluated numerical solution for the electric potential, and an explicit solution for the electrical resistivity of a composite material consisting of a dilute concentration of such embedded disks in an otherwise uniform conductor.
An innovative method for antenna arrays beam configuration is presented. In the proposed method, every element of the array is connected to its feed through a switch, so that it can be active or passive, depending on the switch position. Pattern reconfigurability is achieved by appropriately switching on or off the array elements. The optimal configuration of the switches for each of the radiated patterns, as well the common voltages of the active elements, is calculated by using a genetic algorithm. For each configuration, the currents in the driven and parasitic elements are determined, via their self and mutual impedances, by inversion of the impedance matrix. In the presented examples, the method has been applied to both linear and planar arrays of parallel dipoles that switch the power pattern from a pencil to a flat-topped beam (linear array) or to a footprint pattern (planar array).
This paper propose a new multiple-input multiple-output (MIMO) signal processing scheme that combines optimum transmit and receive beamforming with the Alamouti space-time block code (STBC) transmission and modifies the decoding process. The scheme uses double antenna array groups to achieve stable performance regardless of direction of arrived (DOA) and angular spread (AS). In a multiuser MIMO communications scenario, the beamforming suppresses co-channel interference (CCI) by maximizing the uplink signal-to-noise-plus-interference-ratio (SINR) and suppress CCI independently while preserving orthogonality of the MIMO channel. It is shown that the beamforming process provides array gain by increasing the bit-error-rate (BER) performance and maximizes the available uplink channel capacity for each user in the presence of CCI.
This paper presents an investigation for the electromagnetic scattering characteristic of the 2-D infinitely long target located above two-layered 1-D rough surfaces. A finite-difference time-domain (FDTD) approach is used in this study, and the uniaxial perfectly matched layer (UPML) medium is adopted for truncation of FDTD lattices, in which the finite-difference equations can be used for the total computation domain by properly choosing the uniaxial parameters. The upper and lower interfaces are characterized with Gaussian statistics for the height and the autocorrelation function. For the composite scattering of infinitely long cylinder and underlying single-layered rough surfaces as an example, the angular distribution of scattering coefficient with different incident angles is calculated and it shows good agreement with the numerical result by the conventional method of moments. And the influence of some parameters related to the twolayered rough surfaces and target on composite scattering coefficient is investigated and discussed in detail.
Blind direction of arrival (DOA) estimation algorithms of coherent sources using multi-invariance property is presented in this paper. ESPRIT-like algorithm in [23] can estimate DOA of coherent signal, but its performance is without satisfaction. We reconstruct the received signal to form data model with multi-invariance property, and then multi-invariance ESPRIT and multi-invariance MUSIC algorithms for coherent DOA estimation are proposed in this paper. Our proposed algorithms can resolve the DOAs of coherent signals. They have much better DOA estimation performance than ESPRITlike algorithm. Meanwhile they identify more DOAs than ESPRIT-like algorithm. The simulation results demonstrate their validity.
This paper presents a formulization of time domain (TD) discrete electromagnetic (EM) solution to provide an effective analysis over a variety of EM problems. This procedure first represents the time responses of EM fields in terms of a set of selected basis functions. Their coefficients are then employed to create matrix-form Maxwell's equations with forms analogous to frequency domain (FD) Maxwell's equations, which allows one to formulate TD solutions via utilizing their corresponding FD solutions that are existing and generally much mature. This work provides general characteristics with parts previously described in the discrete-time EM theory [20, 21] and, most importantly, provides rigorous theoretical derivations in formulating the TD solutions.
In this paper, we improve the Ge-Esselle's (GE's) method and apply it to calculate the multilayered Green's functions in the shielded structures. In the improved GE's method, 1) the poles are first extracted using a recursively contour integration method [1]; 2) then the general pencil-of-function (GPOF) [2] is performed to approximate the part of the spectral-domain Green's functions (with the poles contributions being extracted) just along the real axis of kρ plane instead of the rooftop shaped path defined in [3]; 3) Subsequently, the GE's analytical method is employed to obtain the spatial-domain Green's functions. In step 2), a smoothing procedure is also performed here to eliminate the abrupt peak of the sampled spectral-domain Green's function caused by the finite machine accuracy of the poles locations. The numerical results in this paper show that the improved GE's method can accurately and efficiently calculate the Green's functions in the shielded multilayered structure.
This work is about evaluating radar performance in detection of targets embedded in a clutter following Non centered chi-2 Gamma distribution model. This model, also called NG-distribution model, is able to fit high resolution sea radar clutter. In this paper, NG model is described. The performances of CA-CFAR radar, namely probability of detection and probability of false alarm, are calculated and closed forms of these probabilities are achieved. In order to evaluate the obtained results, simulation and analytical results are compared. Good matching between these results is achieved.
A compact Pi-structure transformer operating arbitrary dual band is proposed in this paper. To achieve the ideal impedance matching, the exact design formulas with no restrictions are obtained. In addition, it is found that there are infinite solutions for this novel transformer considering the fact that three independent variables exist in two equations. And to verify the design formulas, the reflection characteristics in different cases are shown by numerical simulations. The horizontal length of this transformer is half of the Monzon's dual band transformer. The proposed dual band transformer can be used in many compact dual band components design such as antennas, coupler and power dividers.
This paper studies the correlation of a receiving thin dipole with an arbitrary load in both anechoic chamber (AC) and reverberation chamber (RC). In both cases, the method of moments is employed to calculate the current distributions along a thin dipole induced by external fields. In AC, a plane wave with a fixed incident angle and polarization is illuminated on the dipole; whereas in RC, the field is represented by an appropriate superposition of many incident plane waves with stochastic incident angles, polarizations and phases. Numerical results for the current distributions of a thin dipole with different loads and electrical lengths are presented and discussed in both chambers. It is demonstrated that the ratios with respect to current magnitudes at the arbitrary load of the thin dipole between AC and RC are determined by its directivity. In particular, the ratios with respect to current magnitudes along the entire dipole whose electrical length is less than half a wavelength are nearly constants regardless of the terminating load, which indicates that results obtained in both chambers are well correlated.
We present here a new pattern with compact size of Ultra Wideband (UWB) microwave filter. The filter is based on quarter-wave length short-circuited stubs model. We introduced here a new schematic model by extracting all parasitic elements such as T-junction and discontinuity in our new pattern of UWB filter. This new filter has minimal number of vias and improved frequency bandwidth, insertion loss and return loss. It is fabricated on RT Duroid 5880 with 0.508mm of substrate thickness. The final dimension is measured as 21mm×14 mm. It is not only compact, but also delivers excellent scattering parameters with magnitude of insertion loss, |S21| lower than 0.85 dB and return loss better than -11.6 dB. The fractional bandwidth is 109% from 3.06 GHz to 10.43 GHz. In the pass band, the measured group delay varies in between 0.47 ns to 0.32 ns, showing stability with minimum variation of only 0.15 ns.
This paper presents performance analysis of cellular CDMA in presence of beamforming and soft handoff. A stop and wait ARQ scheme has been assumed for data service. Joint effects of beamforming and soft handoff reduce delay, BER and increase throughput significantly. Impact of several parameters of soft handoff and beamforming on data performance has been evaluated. Both the cases of perfect and imperfect beamforming have been investigated. Effects of DOA (Direction of arrival) estimation error have also been indicated on data service.
In our previous works, we have presented one differential method for the efficient calculation of the modal scattering matrix of junctions in rectangular waveguides. The formalism proposed relies on the Maxwell's equations under their covariant form written in a nonorthogonal coordinate system fitted to the structure under study. On the basis of a change of variables, we show in this paper that the curvilinear method and the generalized telegraphist's method lead to the same system of coupled differential equations.
A validation process, in which simulations and measurements are compared, is necessary to have confidence in the results obtained by numerical methods that solve scattering problems. This paper presents Radar Cross Section (RCS) measurements of new targets suitable for electromagnetic software comparison and validation. These measurements can be used as an RCS reference data for testing existing and future codes, as well as for the analysis of the scattering mechanisms.
In this paper, we present a fast method to predict the monostatic Radar Cross Section (RCS) in high-frequency of a cavity, which can be modeled as a succession of bent waveguides of the same cross section and stuffed by a perfectly-conducting termination. Based on a modal analysis combined with the Kirchhoff Approximation, this method allows us to obtain closed-form expressions of the transmission matrix at each discontinuity. In addition, to improve the efficiency, a selective modal scheme is proposed, which selects only the propagating modes contributing to the scattering. Compared to the Iterated Physical Optics (IPO) method and the Multi-Level Fast Multipole Method (MLFMM, generated from the commercial software FEKO), this approach brings good results for cavities with small tilt angles of the bends, typically smaller than 2 degrees.
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