In order to eliminate the negative influence of the rotational phase component (RPC) of target prominent scattering centres on the performance of Doppler centroid tracking (DCT) method, a coherent phase compensation method is proposed. The coherence of echo pulses sampled directly in intermediate frequency (IF) is firstly analyzed and proved. Based on the coherence property, the proposed approach improves the translational phase component (TPC) estimation accuracy of DCT. Compared to the modified Doppler centroid tracking (MDCT) algorithm, the proposed method achieves better phase compensation performance with simpler operations. Both the theoretical analysis and experimental results based on the real ISAR data prove the effectiveness and efficiency of the presented strategy.

A new method for broadening the impedance and the axial-ratio (AR) bandwidths of circular polarized microstrip antennas (CPMAs) is proposed. It has improved the bandwidths of a reference antenna greatly without enlarging the antenna size or deteriorating circular polarized radiation characteristics by placing four sequentially rotated parasitic split-ring resonators (SRRs) around the patch of the reference antenna and embedding four defeated ground structure (DGS) elements on the ground plane. Improvements of 51.3% and 49.8% in the impedance and the axial-ratio bandwidths of the antenna are achieved in simulation, respectively. The simulated -10dB impedance and 3dB axial-ratio bandwidths of the antenna have been improved from 101.1 MHz (4.12%) to 153.0 MHz (6.26%) and from 25.1 MHz (1.02%) to 37.6 MHz (1.54%).

In this paper, a dual-mode dual-band microstrip bandpass filter utilizing asymmetric square loop resonators is proposed. A pair of bent open-circuited stubs is installed to the loop as perturbation stubs. By stretching the perturbation stubs more than half-wavelength of the loop, the degenerated modes in a loop are split for dual-band operation. Two asymmetric resonators are cascaded to form two bands. Even- and odd-mode analysis method is used to deduce the resonant frequencies of two bands. Based on the transmission line theory, resonant frequencies of the two resonances are derived. According to the resonant conditions, a kind of dual-mode dual-band bandpass filter can be easily designed. Finally, a dual-band filter with two bands centering at 1.9 GHz and 2.6 GHz is designed in a comprehensive way. Measured results of experimental circuit show good agreement with simulated responses.

In this paper, a novel dual-band bandpass filter with a tunable passband is proposed. Based on two quarter-wavelength resonators and one half-wavelength resonator, dual-band character is designed by introducing two independent coupling paths. The filter structure is designed and can be divided into two parts. The Transmission Zeros (TZs) are derived through simulation. By varying the reverse bias voltage applied to the varactor diodes which are connected to the resonators, the first passband can be independently tuned. The second passband can be easily controlled by the width of the half-resonator. Finally, simulation results show a first tunable passband with a constant fractional-bandwidth of 3.9 ± 0.3 %, a center frequency of 1.472-1.886 GHz, and the second passband almost remains constant with a fractional-bandwidth 2.4% at frequency range 2.24 GHz. The measurement of the fabricated example shows good agreement with the simulation.

Small phased-array antennas can be combined with dielectric lenses or planar lens-arrays to form directive beam-steering system. The use of the lens increases the size of the radiating aperture and enhances the directivity of the phased array, but it also reduces its scan field of view. However, the effect can be controlled by properly designing the phase delay profile across the lens. This paper presents the formulation and methodology for designing modified lenses that can allow the desired scan angle. The utility and limitations of the proposed approach will be illustrated by considering several design examples. Simulations suggest that a directivity enhancement of > 2 dB and wide scan field of view (up to 45° off boresight) can be obtained for compact radiation systems employing small lenses and short separations between the lens and phased array. Larger directivity improvements in the range of tens of dB's are possible in systems with limited scanning capability by employing large lenses and greater phased array-lens separation. Ease of implementation and the ability of the proposed topology to adapt to the system requirements make this topology an interesting candidate for various millimeter-wave radio applications.

A compact printed antenna for WWAN tablet computer application is proposed in this article. The designed antenna occupies a small area of 35×12 mm², which is small enough to be incorporated in a tablet computer, and is placed close to the edge of the shielding wall with a distance of 10 mm. The antenna has a simple structure of comprising a long coupling strip and a feeding strip to capacitively excite the long coupling strip. In this scheme, a chip inductor (L = 25 nH) is loaded on one branch of the feeding strip, which can form a parallel resonant structure to enhance the bandwidth of the lower band. As a result, two wide operating bands to cover GSM850/900 and GSM1800/1900/UMTS2100 operation are obtained with desired 3:1 VSWR. The proposed antenna is an all-printing structure with low production cost, which is especially suited for the thin-profile tablet computers.

A profile reconstruction method using a surface inverse currents technique implemented on GPU is presented. The method makes use of the internal fields radiated by an equivalent currents distribution retrieved from scattered field information that is collected from multiple incident fields. Its main advantage over other inverse source-based techniques is the use of surface formulation for the inverse problem, which reduces the problem dimensionality thus decreasing the computational cost. In addition, the GPU implementation drastically reduces the calculation time, enabling the development of real time and accurate geometry reconstruction at a low cost.

In this paper we explore electromagnetic behavior of arbitrarily oriented biaxially anisotropic media; specifically with respect to reflection and transmission. The reflection and transmission of electromagnetic waves incident upon half-space and two-layer interfaces are investigated. The waves may be incident from either the isotropic region or the biaxial region. The biaxial medium considered may be aligned with the principal coordinate system or may be arbitrarily oriented. Critical angle and Brewster angle effects are also analyzed.

Superdirective beamforming can highly reduce the aperture size of high-frequency receive array. At the same time, the closely spaced elements of a small aperture array can make it low efficiency and sensitivity to the array uncertainty, which limit its application in practice. Using a parameter called sensitivity factor, we found that array efficiency and robustness against array error could be considered simultaneously. On that basis, we derive a novel superdirective beamforming criterion based on a constrained sensitivity factor for the HF circular receive array. New method is analytical and computationally inexpensive. Through making the directive gain with a given sensitivity factor maximum, we calculate the optimal weights of the array elements. To illustrate the proposed method can increase the acceptance of HF superdirective receive arrays in practice, several numerical results are provided.

A 2D finite element electromagnetic model that permits the simulation of a cage induction machine, involving the effects of eddy currents and coupling the field equation with the stator field-circuit equation, has been presented in this paper. Transformation matrix has been derived to incorporate specialized stator winding scheme called the bridge configured winding (BCW) in the coupled field circuit equation. The bridge configured winding scheme is capable of producing controllable transverse force by deliberately imparting asymmetric flux distribution in the machine air-gap. Steady state stator currents have been calculated using the time-stepping scheme with the rotor motion at constant speed allowing the FE model to take into account the harmonics due to the eccentricity (static) of the rotor. This work has furnished us with the 2D magnetic flux distribution in the whole finite element domain as well as sets out an electromagnetic model to study the electromechanical interaction between the eccentric rotor motion and the electromagnetic field. The results, in terms of variation of terminal currents (phase and bridge) and unbalanced magnetic pull (UMP) due to rotor eccentricity as well as asymmetric field (deliberately imparted by exciting the bridge), obtained from the simulation have been compared with analytical formulations as well as already published experimental results.

A novel side-feed quasi-Yagi type antenna capable of triple-frequency operation at about 1900, 2400 and 3600 MHz is presented in this paper. The antenna is composed of a folded quasi-Yagi element and a modified CPW-to-CPS transition. The proposed antenna can be mounted perpendicularly to the feed circuit board of an array antenna so that it offers a novel design with a free degree of feed point so as to save device space, and its folded quasi-Yagi element can result in a low profile to the system. The experimental results demonstrate that the proposed antenna can operate over three frequency bands, with -10 dB reflection coefficient bandwidths of 200 MHz, 200 MHz, and 400 MHz at the central frequencies of 1.9, 2.4, and 3.6 GHz, respectively. Moreover, in the whole working bands, the antenna basically keeps the same radiation pattern and the gain is over 2.6 dBi.

A general design procedure of decoupling networks, between two coupled antennas, is proposed using a single transmission line connected between the input ports of the antennas at a specified distance. A rigorous analysis for the decoupling circuit is introduced considering the return loss of the antennas into calculations. Furthermore, using numerical optimization, enhancement of decoupling between the antenna ports achieved. Full-wave analysis and measurements are provided to verify the proposed technique.

In this paper, a novel dual-band bandpass filter (BPF) based on a single short-ended dual-mode resonator (SEDMR) is presented. According to the voltage distribution of the resonator, two pairs of loaded open stubs, inside and outside of the resonator, are utilized to tune the center frequency and the external quality factor of the first passband respectively, while there is no influence on the second passband. Meanwhile, source-load coupling is introduced to produce transmission zeros to improve the passband selectivity and band-to-band isolation. For demonstration, a dual-band filter working at 1.52 GHz for GPS and 3.5 GHz for WiMax is designed, fabricated and measured with insertion losses of 1.47 and 0.95 dB. In addition, two transmission zeros, introduced by source-load coupling, located at 2.19 and 2.67 GHz between the first and second passband improve passband selectivity and band-to-band isolation better than 50 dB.

A coplanar waveguide (CPW)-fed Archimedean spiral antenna with band notched characteristics is presented for ultra-wideband (UWB) applications. The proposed antenna consists of a two-arm spiral fed by a CPW line. The novelty of this design is integrating three inverted U-shaped slots within the feeding line of the spiral antenna to introduce frequency band notched characteristics at 5.8 GHz. This antenna covers the frequency range from 3.1 GHz to 10.6 GHz with VSWR less than 2, except at a band rejection frequency of 5.8 GHz. Simulated and measured data are presented to verify the proposed design.

A new configuration of Yagi antenna is proposed, which can improve the forward/backward ratio (f/b) significantly while maintaining a high gain. This configuration involves the addition of one radiating element (dipole) to the original Yagi array which produces a controllable pattern used for cancellation of back lobe. This additional element may arrange on parallel (side-by-side) or collinear to a radiating dipole of the original Yagi antenna. It is shown here that the technique is most effective for collinear configuration (exhibits smaller mutual effects) and that there then exists an optimum length and position for the added element. The amplitude of the excitation of the additional element determines the angular location of the back lobe reduction. To demonstrate the major benefits, comparisons are made among the proposed and conventional Yagi configurations. Numerical and measured results of our design show more than 20 dB front to back ratio at 2.4 GHz. To the author's knowledge, this is the first printed Yagi antenna presented that has a high gain and a high f/b ratio designed using simple technique. Moreover, the proposed array represents a simple and valuable alternative to the stack Yagi antennas as the obtainable radiation characteristics are satisfactory in terms of both forward and backward gain.

This paper presents a frequency domain technique for reconstructing the constitutive parameters of inhomogeneous planar layered chiral media based on an optimization approach. The measured co- and cross-reflection and transmission coefficients are used to extract profiles of electromagnetic parameters of the inhomogeneous chiral media. To identify the functions of constitutive parameters of the chiral media, Fourier series expansions and Genetic Algorithm (GA) are utilized. Since the optimization problem is highly non-linear, enhanced GA in which a fuzzy system is used for improving the speed and accuracy of GA. The performance and feasibility of the proposed reconstruction method is proven using two typical examples.

In this paper, the fast Fourier transform (FFT) to perform spatial convolutions of the time domain discrete Green's functions (DGF) method related to the analysis of the antenna with more than one dimension has been proposed. For this aim, the discrete Green's functions and the currents on the antenna have been appropriately defined periodic so as to use the zero padded fast Fourier transform. The computational complexity of this approach is O(N_wN_xN_yN_z log(N_xNyN_z)), contrary to O(N_wN_x²N_y²N_z²)for direct implementation of the convolutions. Simulation results demonstrate the great efficiency of the FFTbased spatial convolutions in the modeling of planar antennas.

This paper considers an electromagnetic waveguide composed of two periodic, perfectly conducting, rippled surfaces. This periodic system has a band structure given by a dispersion relation that allows us characterize eigenmodes of the system. We considered the cases of both smooth and rough surfaces, using an integral numerical method to calculate field intensities corresponding to eigenmodes over a wide frequency range. Under certain conditions, the system presents disordered patterns of field intensities with smooth surfaces. We believe that the explanation of disordered patterns is the following: for smooth surfaces, the phenomenon of electromagnetic chaos; and for rough surfaces, the speckle phenomenon. Since it is well known that the surfaces of materials always have a certain degree of roughness, it can be concluded that both chaos and speckle contribute to the presence of disordered field patterns.

This work deals with the behavior of a patch antenna equipped with squared electromagnetic bandgap (EBG) structures and subjected to various mechanical deformations (twisting and bending deformations). The EBG structures have a stop band frequency (rejection) feature, allowing the coupling and the undesired electromagnetic interferences to be reduced. The influences of the deformations on the mutual coupling and radiation patterns of an antenna equipped of those EBG elements are experimentally studied.

In this paper, we show that the solution of linear coupled mode equations (LCME) is a good approximation to that of the nonlinear coupled mode equations (NLCME) for small times, provided that the nonlinearity is weak. We bound the difference between the two solutions using energy estimates. We illustrate our findings in numerical examples.