This paper presents a design approach for dual-band Wilkinson power dividers. Two pairs of parallel coupled-lines are used to replace the quarter-wavelength transformers in the conventional Wilkinson power divider to obtain dual-band operation. Using even- and odd-mode analysis, the closed-form design equations are derived for design parameters and design procedures of the proposed dual-band power divider are given. For verification purpose, a practical power divider, which operates at 1 GHz and 2.1 GHz with 3 dB power dividing ratio, is designed, fabricated and tested. The simulated and measured results are in good agreement.

Effects on the communication signals caused by the time-varying plasma sheath surrounding hypersonic vehicles are investigated. Using computational fluid dynamics (CFD) technique, Demetriades's plasma turbulence model and finite-difference time-domain (FDTD) algorithm, amplitude variation and phase fluctuation induced by plasma electron density turbulence are obtained, and their statistical properties are analyzed and characterized. Furthermore, a finite-state Markov channel (FSMC) model is proposed, to represent the dynamical effects on electromagnetic wave propagation through plasma sheath. With high accuracy and greatly reduced complexity, the FMSC model could be very useful to develop novel communication techniques for alleviating the radio blackout problem.

While Archimedean spiral antennas were invented a half-century ago, only self-complementary impedance can be evaluated directly from the Babinet's principle. This paper examines the effects of metal width and arm spacing on printed spiral's input impedance. A model is proposed based on examination by decomposition of planar spiral. A closed-form expression for the input impedance of Archimedean spiral antenna is obtained by evaluating the proposed model with conformal mapping techniques. Full-wave numerical simulations, Babinet's principle, and a fabricated antenna demonstrate the accuracy of the proposed model. The expression in this work can be used to find the impedance of a variety of spiral complementary structures analytically. The examination and discussion on the effects of other parameters and features in addition to the spiral itself are also provided through numerical simulation.

A small patch antenna is associated with passive (reactively loaded) elements (varactors) in order to auto adjust the resonant frequency in a single-channel multi-frequency configuration appropriate for biomedical applications. As a supplementary study of the authors in the field of detection of temperature abnormalities in human tissue phantom using microwave radiometry, this paper adds a contribution to frequency readjustment when a shift occur due to the fact that the human body is a complex and stratified dielectric object. The optimization of the array is performed using a Genetic Algorithm (GA) tool as a method of choice. The adjustment in the measurement frequency is performed by altering the values of the passive elements according to the shift needed.

In this paper, we present a novel 3rd filtering power divider with high in-band isolation. The proposed device employs six quarter-wavelength resonators and six internal isolation resistors symmetrically arranged to require the power division and filtering function. Based on the circuit topology, the multiple resistors can be integrated to obtain a good isolation and port impedance matching. Compared to the conventional power divider with bandpass response, the new device is easy to realize a high-order design with a good isolation. For demonstration, a prototype operating at 1.5 GHz with more than 20 dB in-band isolation is implemented. Simulated and experimental results agree well, validating the proposed methodologies.

The performance of smart antenna greatly relies on the efficient use of direction-of-arrival (DOA) estimation techniques for both coherent and non-coherent signals. In practice, DOA estimation problems and difficulties increase when the signals in multipath propagation environments are highly correlated or coherent. Therefore, exploring an algorithm which is capable of estimating coherent signals is of great importance. To overcome this problem, a new high-resolution modified virtual singular value decomposition (MV-SVD) algorithm for DOA estimation of coherent signals is proposed. It is based on the hybrid combination of the virtual array extension, singular value decomposition (SVD), and modified MUSIC algorithms. The proposed algorithm provides many features such as: decorrelation of the coherence between the signals without reducing the rank of the covariance matrix or losing the array aperture size; high-resolution and more stability especially at low SNR values; and an increase in the maximal number of detectable signals to M-1, where M is the number of antenna elements.

An improved method of quality guided phase unwrapping (QGPU) is proposed in this work. It extracts the quality map via a median filtered phase derivative variance (MFPDV) that applies a twodimensional median filter on the phase derivative variance (PDV) map, in order to reduce the effect of noise in the background area. In addition, we employed the Indexed Interwoven Linked List (I2L2) structure to store the orderly adjoin list more efficiently and the Two Section Guided Strategy (TSGS) to reduce comparison frequency. The experiments demonstrate that the normalized L1 norm of MFPDV of a brain MR image is only 0.0827, less than that of PDV method at 0.0923. Besides, the computation time of QGPU with I2L2 technique is only 30% of that with sequence structure, and the computation time of QGPU with TSGS is only 65% of that without TSGS. In total, the proposed MFPDV upwrap phase images better than conventional PDV map, and I2L2 and TSGS are efficient strategies to reduce computation time.

We use a gradient-based material distribution approach to design conductive parts of microstrip antennas in an efficient way. The approach is based on solutions of the 3D Maxwell's equation computed by the finite-difference time-domain (FDTD) method. Given a set of incoming waves, our objective is to maximize the received energy by determining the conductivity on each Yee-edge in the design domain. The objective function gradient is computed by the adjoint-field method. A microstrip antenna is designed to operate at 1.5 GHz with 0.3 GHz bandwidth. We present two design cases. In the first case, the radiating patch and the finite ground plane are designed in two separate phases, whereas in the second case, the radiating patch and the ground plane are simultaneously designed. We use more than 58,000 design variables and the algorithm converges in less than 150 iterations. The optimized designs have impedance bandwidths of 13% and 36% for the first and second design case, respectively.

A dual-band circularly polarized antenna is presented in this paper. A rectangular patch antenna with gap-feeding structure is firstly designed, and 3-dB axial-ratio bandwidth from 2.35 to 2.48 GHz is obtained. A parasitic square ring is placed on the rear of the rectangular patch as a band-notch unit operating around 2.4 GHz. Then an original wide circularly polarized band is split into two bands from 2.25 to 2.31 GHz and from 2.46 to 2.53 GHz. By adopting differential feeding, symmetrical patterns are achieved. Measurement results show that two 3-dB axial-ratio bands of 2.6% (2.25-2.31 GHz) and 2.0% (2.51-2.56 GHz) are obtained with a small frequency ratio of 1.11.

In this paper, a bi-layer twisted split-ring structure asymmetric chiral metamaterial was proposed, which could achieve circularly polarized (giant circular dichroism effect) wave with dual bands and linear polarization transformation (giant optical activity)with asymmetric transmission wave emissions simultaneously from linearly polarized incident wave at microwave frequencies. Experiment and simulation calculations are in good agreement, indicating that the dual-band circular polarizer features high conversion efficiency around 5.32 GHz and 6.6 GHz in addition to large polarization extinction ratio of more than 16 dB, while cross linear polarization transformation with asymmetric transmission is observed around 10.52GHz. The transformation behavior for both circular and linear polarizations could be further illustrated by simulated surface current and electric field distributions. The proposed asymmetric chiral metamaterial structure could be useful in designing novel EM or optical devices, as well as polarization control devices.

The microwave polarimetric scattering from two-dimensional (2-D) wind fetch- and water depth-limited nearshore sea surface is investigated by using the second-order small-slope approximation (SSA-II). The sea waves are simulated by taking into account the influences of fetch and depth. Based on this, the joint influence of fetch and depth on the normalized radar cross section (NRCS) of sea surfaces for both co-polarizations and cross-polarization in different wind directions is mainly studied. Monostatic and bistatic numerical results both indicate that in the marine environment of small depth and large fetch, the nonlinear interactions among waves become more intense, which has a greater impact on NRCSs for co-polarizations than their cross-polarized counterparts. Comparison of the results for different wind directions also reflects that the backscattered echoes along wind direction have much greater strength, regardless of the magnitude of wind fetch and water depth.

The flux and torque of switched reluctance motor (SRM) have a highly nonlinear functional relationship with rotor position and phase current, as a consequence of the double-salient structure of the stator and rotor pole and highly magnetic saturation, which is difficult to build an accurate analytic model. In order to achieve the SRM high-performance control, it is necessary to build an accurate nonlinear model for SRM. On the basis of the adequate and precise sample data, by taking advantage of neural network that has outstanding nonlinear mapping capability, this paper adopts the Back Propagation (BP) based on Levenberg-Marquardt (LM) algorithm and Radial Basis Function (RBF) neural networkto build offline models for SRM respectively. Under different requirements of model accuracy, two kinds of network are studied and compared with each other on accuracy, scale and other aspects. The research results indicate that the network scale built as SRM nonlinear model by BP neural network based on LM algorithm is smaller than the one built by RBF. Additionally, the model accuracy is higher. In terms of the Switched Reluctance Drive (SRD) which requires real-time controller, reducing the network scale will be beneficial to the online real-time control of the system.

To reduce the complexity of classifier design in radar automatic target recognition (RATR), a novel RATR method for high range resolution profile(HRRP) is proposed. Linearly separable features are extracted with sequential vanishing component analysis (SVCA) which is implemented by finding the generators of each approximately vanishing polynomial set, and target classification is implemented with linear classifiers. Experiments are carried out on simulated vehicle target data and MSTAR database, and the results demonstrate the efficiency of the proposed method.

In this paper, a delivery system allowing simultaneous microwave heating and real-time spectrofluorometric measurements in biological systems is proposed and characterized. This system is used to investigate the phase behavior of lipid bilayers from about 15°C to 45°C. The delivery system is based on an open transverse electromagnetic (TEM) cell combined with a spectrofluorometer via an optical cable system. A numerical and experimental dosimetry of the delivery system is conducted. The Specific Absorption Rate (SAR) efficiency of the system is 26.1±2.1 W/kg/W. Spectrofluorometric measurements on Laurdan labeled small unilamellar vesicles (SUVs) are carried out. Generalized polarization (GP) of the SUV' membrane is obtained from the fluorescence intensities measured at two emission wavelengths.

This paper deals with the modeling of the brushed DC motor used as a reinforced starter for a micro-hybrid automotive application. The aim of such a system, also called ``stop-start'', is to stop a combustion engine when the vehicle pulls to a stop, and to restart it when the driver accelerates. A reinforced starter is able to ensure this new function in addition to the classical cold start. Then, its life time has to be widely increased in comparison with a classical starter. They have to be optimized, and more especially their process of commutation in order to minimize commutator and brush wears, and thereby increase the lifetime of the device up to the whole life of the vehicle. The main contribution of the paper is the development of a coupled FE-circuit model taking into account local saturation and arc phenomena. Brush-segment contact resistance introduced in the circuit model has been computed efficiently and compared to measures. The whole model has been validated by experimental measurements which are carried out with specific experimental test benches.

A modified Y-parameters approach is proposed to model the behavior of coupled oscillator arrays (COA's). A coupling network with tunable coupling strength is proposed, which has a near-constant input conductance, to ensure the oscillation condition under different attenuation levels. The parameters of oscillators and the coupling network are derived on the TSMC 0.18 μm technology, and their Y parameters are extracted around 10 GHz for illustration. After being verified with full-circuit simulations and other behavior models, including the Adler's equation and the conventional Y-parameters approach, this method is applied to estimate the maximum allowable number of oscillators that can be coupled together. The inter-element phase shift of a COA is controlled by tuning the free-running frequencies of oscillators at both ends. Injection signals with proper phases are proposed to synchronize multiple COA's into a bigger COA.

In this paper, a novel microstrip-fed compact antenna with triple band-notched characteristics is presented for ultrawideband (UWB) applications. The antenna consists of a circular radiating patch, a 50 Ω microstrip feed line, a partially slotted ground plane, and a pair of modified capacitance loaded loop (MCLL) resonators. The novel resonators are symmetrically located in the vicinity of the feed line to achieve triple band-notched characteristics, such as 3.4-3.7 GHz for WiMAX, 5.15-5.825 GHz for WLAN, 7.25-8.395 GHz for X-band satellite communication. The good performance of triple notched bands, stable gain and omnidirectional radiation patterns in the operating bands make the proposed antenna a good candidate for UWB utilization.

A novel ultra-wideband (UWB) bandpass filter (BPF) with notched band based on microstrip/slotline ring resonators is presented in this paper. The UWB BPF is fabricated with two microstrip ring resonators on the top copper layer and a slotline ring resonator on the bottom ground layer. Thus, an ultra-wide passband can be achieved owing to the coupling effects and microstrip/slotline transitions of these three ring resonators. Then, a notched band which is created at 8.0 GHz for satellite communication system is designed based on loaded short-circuited stubs. Both the simulated and measured results show that this compact UWB BPF has good performances of wide passband and notched band.

A novel coplanar waveguide (CPW)-fed tri-band monopole antenna for WLAN/WiMAX applications is presented. To get a compact antenna size, meandering and coupling technologies are used here. Meanwhile, with the loading method, the higher mode is used to cover the required band. The antenna has a very small size of only 18×28 mm². The measured and simulated results show that the proposed antenna has three separate 10-dB impedance bandwidths of 220 MHz (2.36-2.58 GHz), 470 MHz (3.36-3.83 GHz) and 1460 MHz (4.83-6.29 GHz), which can cover all the 2.4/5.2/5.8 GHz WLAN and 3.5/5.5 GHz WiMAX bands. Good dipole-like radiation characteristics are obtained over the operating bands.

A coupled-line-based planar antenna for single-band and dual-band operation is presented. The well-known uniplanar coupled inverted-L antenna (UCILA) has a simple and specific mechanism to achieve the dual-band ratio that was not described in the past. The UCILA which shunted a short stub in the slotline portion can provide switchable modes among single-low band (3.4% for WLAN 2.44 GHz), single-high band (15% for WLAN 5.2-5.8 GHz band) and dual-band (WLAN 2.44/5-6 GHz) operations.