This paper presents a flexible and generic broadband RF predistortion linearizer designed using backward reflection topology that can correct for the dualinflection point type compression characteristics usually encountered in the gain profile of metal semiconductor field effect transistor (MESFET) based power amplifiers. It employs circuit configuration of two parallel Schottky diodes with one p-intrinsic-n (PIN) diode in parallel, connected at two ports of a 90°hybrid coupler. The Schottky diodes are coupled via a quarter wave transmission line segment which generates dual inflection points in the gain characteristics of the linearizer. The incorporation of a PIN diode helps in improving the achievable range in the gain and phase characteristics of the linearizer. Overall, the linearizer is capable of linearizing various types of power amplifiers owing to the flexible control on the linearizer's parameters and eventually the gain and phase characteristics of the linearizer. The proposed linearizer can be employed in the frequency range of 1.4-2.8 GHz and can simultaneously improve the third- and fifth-order intermodulation distortions. The measurements carried out on a commercial ZHL-4240 gallium arsenide field effect transistor (GaAs FET) based power amplifier demonstrates the broadband functionality of the proposed linearizer.

The Moment Method is used to estimate the error induced by a compact measuring probe in the near-field. A crossed-dipole is used as a compact near-field measuring probe of a waveguide radiator in an infinite ground plane, since it measures both co-pole and cross-pole components simultaneously. However, due to multiple reflections between radiator and probe, in addition, mutual coupling effects between the poles, near-field values are changed. The relative sampled electric field pattern (without the probe) is compared to the relative sampled co-pole voltage pattern in the scan plane and the induced error is computed. The radiating waveguide's reflection coefficient is altered with respect to the reflection coefficient when there is no probe in the near-field. The numerical results concerning the reflection coefficient without the probe are compared to the measured values, and good agreement is observed.

Application of multi-dimensional Cauchy approximation and coarse-discretization electromagnetic (EM) models to surrogate-based optimization of microwave structures is discussed. Space mapping is used as an optimization engine with the surrogate model constructed as a Cauchy approximation of the coarsely discretized device EM model. The proposed approach allows us to perform computationally efficient optimization of microwave structures without using circuit-equivalent coarse models traditionally exploited by space mapping algorithms. We demonstrate our technique through design of a range of microwave devices, including filters, antennas, and transitions. Comprehensive numerical verification of the proposed methodology is carried out with satisfactory designs obtained --- for all considered devices --- at a computational cost corresponding to a few fullwave simulations.

The spectral switch phenomenon of light induced by scattering from a collection of particles is, to the best of our knowledge, reported for the first time. It is shown that when a spatially coherent light wave with a spectrum of Gaussian distribution is scattered from a collection of particles, the rapidly transition of the spectrum of the scattered field from red shift to blue shift (i.e., spectral switch) can be observed. It is also found that the spectrum of the scattered field will experience several spectral switches with the increase of the scattering angle.

We apply the linear embedding via Green's operators (LEGO) method to the scattering by large finite dielectric bodies which contain metallic or penetrable inclusions. After modelling the body by means of LEGO bricks, we formulate the problem via an integral equation for the total incident currents over the boundaries of the bricks. This equation is turned into a weak form by means of the Method of Moments (MoM) and sub-domain basis functions. Then, to handle possibly large MoM matrices, we employ an order-reduction strategy based on: i) compression of the off-diagonal sub-blocks of the system matrix by the adaptive cross approximation algorithm and ii) subsequent compression of the whole matrix by using a basis of orthonormal entire-domain functions generated through the Arnoldi iteration algorithm. The latter leads to a comparatively small upper Hessenberg matrix easily inverted by direct solvers. We validate our approach and discuss the properties of the Arnoldi basis functions through selected numerical examples.

This paper presents a closed-form analysis of composite right/left handed transmission lines. The ladder network structure of the transmission line allows to obtain a rational form of any twoport network representation. As a consequence of the rational form of the transfer functions, poles and residues are easily computed and the dominant ones selected leading to an efficient time-domain macromodel. The numerical results confirm the robustness and the accuracy of the proposed method in capturing the physics of composite right/left handed transmission lines.

A modified microstrip combline array antenna (MMCA) is designed to obtain wide beamwidth (≈90°) in E-Plane radiation pattern and therefore the better coverage for using in the radio controller systems for avionic application. Beside wide beamwidth, wide bandwidth can be obtained by designing of MMCA in travelling wave mode. Moreover, as will be seen in the paper, to achieve a better performance we need the low sidelobe level and tilted radiation pattern, which can be obtained by suitable tapering the amplitudes of array elements and adjustment the phase difference between them, respectively.

In this paper, a frequency reconfigurable active array antenna (RAA) system, which can be reconfigurable at three different frequency bands, is proposed. The proposed RAA system is designed with a novel frequency reconfigurable front-end amplifiers (RFA) designed with the simple reconfigurable impedance matching circuits (RMC) with the MEMS switches. With the MEMS switch, the RFA is realized without any performance sacrifice especially linear characteristic. The proposed RMC is composed of a series transmission line and a shunt capacitor, and an arbitrary impedance can be transformed to any other impedance value with single switch control for a desired frequency band. The proposed RAA antenna system is composed of the RMC, RFA with the RMC, 2×2 array of reconfigurable antenna elements (RAE), as well as a reconfiguration control board (RCB) for MEMS switch control, and the validity of the proposed RMC, RFA, as well as RAA system, which is presented with the experimental results.

Generalized band structure equation for photonic crystals which containing dielectric rods in metals medium was derived by using the plane wave expansion method. From the band structure, we can study band gap of photonic crystals in both E and H polarizations. Since metals are frequency-dependant materials, modification needs to be done on the plane wave expansion equation to calculate the metallic photonic crystals containing dielectric constant rods. To ease the calculation, simple Drude model for metals are used. In this model, the equation is without damping constant. We have plotted the band structure for photonic crystals in metals medium. Then, we studied the ffective plasma frequency of the structure from the band graph in E polarization mode (TM). We found that effective plasma frequency can be tailored as we want. Detailed results are presented with different sizes of radius. Comparison is made for different background materials.

Guided-wave propagation in chiral H-guides is analyzed, using a building-block approach. In a first stage, a 2D chiral parallel-plate waveguide is studied using a frequency dispersion model for the optically active medium, where the constitutive chiral parameter is assumed to be dependent on the gyrotropic parameter. In the second stage, the mode matching technique and the transverse resonance method are used to characterize the 3D structure. A full parametric study is presented for a fixed frequency. The operational and dispersion diagrams for the chiral H-guide are presented. By replacing the common isotropic slab with a chiral slab, chirality provides an extra degree of freedom in the design of new devices.

The modular toroidal coil (MTC) is composed of several solenoidal coils (SCs) connected in series and distributed in toroidal and symmetrical forms. In this paper, we present an accurate approach for calculation of the mutual and self-inductance between all the SCs of MTC with any arbitrary section. We use Biot-Savart's and Neumann's equations to calculate the self- and mutual inductance between two filamentary circular rings with inclined axes that lie in the same plane, respectively. Their centers are either displaced along the axis of one coil or displaced along one axis of the first coil and then displaced sideways. We use the extended three-point Gaussian algorithm to solve the numerical analysis of the integrations resulting from these equations. Additionally, we apply the filament method to calculate the inductance of the MTC coil. Moreover, the finite element method (FEM) is employed to obtain SC inductance. The results obtained using the FEM confirms the analytical and empirical results. Furthermore, the comparison of the behavior of SC inductance, when the dimensional parameters of the SC are changed, with the FEM results shows an error of less than 0.2%. In this approach, we clarify how the presented equations have to be used for different coil combinations in the filament treatment. Thus, the presented approach can be easily used to calculate the mutual and self-inductance of a MTC between any two MTC rings in three dimensions.

Two different approaches for compensating the probe positioning errors in a near-field-far-field transformation with cylindrical scanning using a nonredundant number of measurements are presented and experimentally validated in this paper. In order to evaluate the uniformly distributed samples from the irregularly spaced ones, the former makes use of the singular value decomposition method, whereas the latter employs an iterative technique. In both the cases, the near-field data needed by a standard nearfield-far-field transformation are efficiently evaluated via an optimal sampling interpolation algorithm.

A simple field analysis was developed for helical slow-wave structure symmetrically supported by rectangular shaped discrete dielectric support rods partially embedded in the metal segments projecting radially inward from a metal envelope for wideband traveling-wave tubes. The tape helix model was used for the prediction of the dispersion relation and the interaction impedance characteristics. The closed form simplified expressions are obtained by combining the tape model dispersion relation for free-space helix and the dielectric loading factor obtained for the loaded helix in the sheath model. The dispersion characteristics and the interaction impedance characteristics obtained by the present analysis were compared with other more involved analytical method reported in the literature for the similar helical slow-wave structure and found to be in close agreement. The present analytical results were also validated against HFSS simulation with an agreement within 5% for both the characteristics for a wide range of structure parameters. An appropriate choice of the structure parameters (helix thickness, height of the metal segments, material of the dielectric support rods, wedge segments angle and helix pitch) provided the phase velocity varying with frequency corresponding to flat to negative structure dispersion with an appreciable interaction impedance values over a wide frequency band. The present analysis enjoys simplicity and establishes the potential of theproposed helical interaction structure for its employment in wideband traveling-wave tubes.

Intelligent compression is important to image transmission in real time over bandlimited channels for synthetic aperture radar (SAR) payloads deployed on unmanned aerial vehicles (UAV), where target areas are encoded with high fidelity, while background data are encoded with lesser fidelity. A target-aided SAR image intelligent compression (TAIC)system is presented in this paper, which utilizes robust fixed-rate trellis-coded quantization (FRTCQ) to encode target sequences and FRTCQ to encode background sequences. Multiresolution constant false alarm rate (CFAR) detector in wavelet domain using db4 based on the multiscale model of target is embedded. Generic region of interest (ROI) mask is created. In order to achieve better quality of target areas decoded, ROI mask is modified. The improved performance using TAIC system by compressing target chips from training set and testing set in Moving and Stationary Target Acquisition and Recognition (MSTAR) database is demonstrated.

This paper describes a study on RF attenuation path loss behavior in suburban coverage within Cyberjaya and Putrajaya areas, located in Selangor State in Malaysia. The objective of this study is to develop and optimize a path loss model based on the existing Hata path loss model and outdoor measurement using frequency range from 400 MHz to 1800 MHz. The optimized model had been used and validated at places within Putrajaya area to find the relative error in order to assess its performance. The values for modified empirical parameters of Hata model were developed and presented in this paper. From the simulation result, the optimized model is found to best fit into the base station located at Putrajaya with smaller mean relative error. The smaller mean error shows that the optimization has been done successfully and thus, this optimized model can be useful to telecommunication providers in Malaysia in order to improve their service for mobile user satisfaction.

In this paper, two-dimensional time-stepping finite-element (TSFE) method is performed for modeling and analyzing of a salient pole synchronous generator with different degree of dynamic eccentricity (DE) fault. TSFE analysis is used to describe the influence of DE fault on the flux distribution within the generator and no-load voltage profiles at low and high field current is obtained for healthy and faulty cases. Comparing the magnetic flux distribution of healthy and faulty generators helps to detect the influence of DE fault. Also, it can be seen at no-load condition with low excitation current, the effect of the eccentricity is considerable compared to that of the rated excitation current. Since the calculation of inductances of the machine is the most important step for fault analysis and diagnosis, the self- and mutual-inductances of the stator phases and rotor windings are calculated in the eccentric generator. Double periodic phenomenon is observed in inductances profile of stator phases due to the DE fault. Finally, spectrum analysis of stator current of two generators with different design parameters is used to diagnosis the significant harmonics in the presence of DE fault.

In this paper, a novel microstrip structure is developed to realize a dual-band bandpass filter. The proposed bandpass structure uses a microstrip resonator with two independently controlled resonance frequencies producing two frequency bands of interest controlled by adjusting the dimensions of the resonator. Parametric analysis is performed on the structure to determine the optimum dimensions to obtain the desired frequency response and is explained in the paper. The dual-band bandpass filter developed in this paper exhibits dual operating frequencies at 1390 MHz and 2520 MHz with 9.85% and 9.92% fractional bandwidths respectively. We achieved a compact second-order dual-band bandpass filter with controllable resonance frequencies and low insertion losses in the passband with high selectivity. The measured results are in good agreement with simulated results. Additionally, it can be easily fabricated and can be used in applications where miniaturization and compatibility with microstrip technology are of primary concern.

This paper presents an approach to the design of a novel dual-band power divider with variable power dividing ratio. To achieve dual-band operation, a novel dual-band quarter-wave length transformer based on coupled-lines is proposed, which is used to replace the quarter-wave length transformer in Wilkinson power divider. The proposed dual-band power divider features a simple compact planar structure with wide bandwidth performance for small frequency ratio. Closed-form design equations with one degree of design freedom are derived using even- and odd-mode analysis and transmission line theory. For verification purpose, power dividers operating at 2.4/3.8 GHz with dividing ratios of 2:1 and 1:1 are designed, simulated and measured. The simulated and measured results are in good agreement.

In this paper, a novel double-printed trapezoidal patch dipole antenna suitable for UWB applications with band-notched characteristic is presented and investigated. The band -notched characteristic is achieved by inserting T-shape slots on the trapezoidal radiating patches. The impedance characteristic, radiation patterns and the transfer function are studied. Experimental results show that the proposed antenna covers the entire UWB band (3.1-10.6 GHz) while it has a notched band for the IEEE 802.11a frequency band (5.15-5.825 GHz). Measured group delay, transmission characteristics and Time domain characteristics indicate that the proposed antenna satisfies the requirement of the current wireless communications systems.

In this paper, the designed of triple-band printed dipole antennas are incorporated with single-band artificial magnetic conductor (AMC). The single-band AMCs are designed to resonate at 0.92 GHz, 2.45 GHz and 5.8 GHz using TLC-32 dielectric substrate. The four important parameters in AMC high impedance surface (HIS) design are also described in this paper. By simulating a unit cell of the AMC structure using a transient solver in Computer Simulation Technology (CST) software, the characteristic of the AMC can be characterized. The AMC condition is characterized by the frequency or frequencies where the magnitude of the reflection coefficient is +1 and its phase is 0°. It has high surface impedance (Z_s) and it reflects the external electromagnetic waves without the phase reversal. This characteristic of AMC enables the printed dipole to work properly when the antenna with AMC ground plane (GP) is directly attached to the metal object. The performances of the antenna with and without AMC structure as a ground plane to the antenna such as return loss, realized gain, radiation efficiency, radiation pattern and directivity are studied. Reported results show that the performances of the antenna are improved. Hence, the designed dipole tag antenna can be used for metal object identifications when the AMC structure is introduced as a ground to the antenna. The properties of the antenna are also remained well when the size of metal plate attached to them is increased.