This paper presents a new dual-band, dual-polarized 1 x 4 antenna array design for telecommunication base station. One of the bands covers global system for mobile communication (GSM) band, while the other covers both digital communication system (DCS) and universal mobile telecommunication system (UMTS) bands. The antenna is based upon an aperture stacked patch layout and incorporates a simple and novel dual-layered feeding technique to achieve dual polarized radiation. For feeding the array elements, a corporate feed network is used. In order to achieve appropriate matching in both bands, a three-section Chebyshev transformer has been designed. The proposed antenna shows good port decoupling, less than -30 dB for dual linear polarization over its operating bands. Peak antenna gains about 11 dBi and 11.6 dBi have been obtained for lower and upper bands, respectively. The effort was directed toward the design of a single standalone dual-polarized antenna to cover all three bands.
Planar waveguide gratings have shown great potential for the application of the wavelength division multiplexing (WDM) functionality in optical communications due to their compactness and high spectral finesse. Planar gratings based on silicon nanowire technology have high light confinements and consequently very high integration density, which is 1--2 orders of magnitude smaller than conventional silica based devices. In the present paper, we will simulate the silicon nanowire based planar grating multiplexer with total-internal-reflection facets using a boundary integral method. The polarization dependent characteristics of the device are analyzed. In addition, the planar grating multiplexer with 1 nm spacing is fabricated and characterized. Compared with measured values, the numerical results show that the sidewall roughness in the grating facets can result in a large insertion loss for the device.
The imaging problem of spotlight synthetic aperture radar (SAR) in the presence of azimuth spectrum folding phenomenon can be resolved by adopting the azimuth deramping-based technique and traditional stripmap SAR imaging algorithm, and this method is the so-called two-step processing approach. However, when the spotlight SAR operates on squinted mode, the echo two-dimensional (2D) spectrum is shifted and skewed due to the squint angle. In such case, the original two-step processing approach is not suitable anymore. This paper presents a novel imaging algorithm using the deramping-based technique and azimuth nonlinear chirp scaling (ANLCS) technique. First, the problem of azimuth spectrum folding phenomenon in squinted spotlight SAR is analyzed. Subsequently, based on the analysis results, the linear range walk correction (LRWC) is applied for removing the squint angle impacts on signal azimuth coarse focusing. At last, a modified azimuth NLCS algorithm is proposed for overcoming the depth of focus (DOF) limitation problem that induced by the LRWC preprocessing. Point targets simulation results are presented to validate the effectiveness of the proposed algorithm to process squinted spotlight SAR data with azimuth spectrum folding phenomenon.
In distributed satellite synthetic aperture radar (DS-SAR), along-track and cross-track baselines couple with each other and change dynamically due to formation flying, which makes it difficult to estimate interferometric baseline accurately. To solve the problem, a novel high-precision baseline estimation approach based on interferometric phase is proposed. By modeling accurate relationship between coupling baselines and two-dimensional (azimuth and range) inteferometric fringe frequency under the ellipsoid earth model, the along-track and cross-track baseline can be estimated separately by interferometric phase decoupling. By selecting several segments from interferometric phase during the whole data-take time and estimating instantaneous baseline of each segment, the dynamic baseline can be obtained via a linear filtering. Besides, to improve the baseline estimation accuracy, Semi-Newton iterative method is applied to acquire high-precision fringe frequency estimation, which can make the baseline estimation achieve centimeter level precision. The simulation validates the approach.
We present a tool to aid the design of periodical structures, such as subwavelength grating (SWG) structures. It is based on the Fourier Eigenmode Expansion Method and includes the Floquet modes theory. Besides, the most interesting implemented functionalities to ease the design of photonic devices are detailed. The tool capabilities are shown using it to analyse and design {three} different SWG devices.
A comprehensive facet model for bistatic synthetic aperture radar (Bis-SAR) imagery of dynamic ocean scene is presented in this paper. An efficient facet scattering model is developed to calculate the radar cross section (RCS) of the ocean surface for Bis-SAR firstly. Further more, this facet model is combined with a bistatic velocity bunching ($VB$) modulation of long ocean waves to obtain the Bis-SAR intensity expression in image plane of ocean scene. The displacement of the scatter elements in the image plane and the degradation of radar resolution in azimuth direction are quantificationally analyzed. Finally, Bis-SAR imagery simulations of ocean surface are illustrated, proving the validity and practicability of the presented algorithms.
This study presents new Wilkinson power dividers using compact stepped-impedance structures and capacitive loads to achieve the required power splitting. This approach can produce additional transmission zeros and effectively suppress the desired stopbands because shunt open stubs realize capacitive loads. This study proposes two equal-split dividers and two unequal-split dividers. For the first equal-split case, one shunt open stub forms the needed capacitor in each transmission path, creating one additional transmission zero in each path. To obtain one more transmission zero in each transmission path, the second Wilkinson power divider uses two shunt open stubs in each path to achieve the same capacitor value as the first divider. This study also tests unequal-split dividers with one and two transmission zeros in each path to confirm that compact stepped-impedance transmission lines and shunt to-ground capacitors can be utilized in unequal power division.
A feasible simulator, of which formulation and mechanism should be simple and time saving, is developed in this paper to overcome the difficulties of prediction on the EM scattering from three-dimensional (3-D) electrically very large ship-sea models. The work in this paper is twofold. First, the sea surfaces are supposed to be a combination of many locally-tilted slightly rough facets with two-scale profiles. The radar return from each local facet is associated to a semi-deterministic scheme which is established by combining the geometric optics limit of Kirchhoff Approximation (KA-GO) with the Bragg components of Bass-Fuks' two-scale model (BFTSM). Furthermore, we associate the complex reflective function of the respective facet by a so-called Phase-modified Facet Model (PMFM), in which the facet's phase is treated approximately as a combination of inherent part that follows a homogeneous random distribution and coherent part associated with the relative path-delay. Second, in companion with the semi-deterministic treatment of the sea scattering model, a hybrid approximate algorithm is proposed to deal with the composite scattering of electrically large ship-sea model, which is entirely evolved through facets (for the sea surface) and wedges (for the ship target). The method of equivalent currents (MEC) and a hybrid frame which combines the four path model (FPM) with the quasi-image method (QIM) are employed to calculate the scattering characteristics of the ship-like target and ship-sea interactions, respectively. The entire simulator is of comparatively significant computational efficiency, and suitable for providing a preliminary prediction on the instantaneous complex reflective functions and normalized radar cross sections (NRCS) mean levels for electrically very large ship-sea model.
new circuit structure is proposed for design of dual-band bandpass filters with a wide upper stopband. The unit cell of the circuit consists of two two-port networks in shunt connection; one is a coupled-line section of λ/4 long followed by a transmission line segment of identical length, and the other has the same elements but cascaded in reverse order, where λ/4 is the wavelength at arithmetic mean frequency of the two passbands. Higher-order circuits can be obtained by directly cascading two or more such cells and show improved frequency selectivity. In addition to on both sides of the passbands, transmission zeros are also created in the rejection bands. Analysis of the unit cell circuit is formulated by the transmission line theory, and design curves for one- and two-cell circuits are provided. In realization, interdigital capacitors are incorporated with the λ/4 coupled sections for compensating the effect of unequal modal phase velocities on the filter performance in the rejection band. Two circuits are fabricated and measured to validate the analysis.
The wire-ground electromagnetic coupling structures are quite common in avionics system electromagnetic compatibility (EMC) analysis. The increasing complexities of physical structures make electromagnetic modeling an increasingly tough task, and computational efficiency is desirable. In this paper, a novel selective mesh approach is presented for partial element equivalent circuit (PEEC) modeling where intense coupling parts are meshed while the remaining parts are eliminated. With the proposed approach, the meshed ground plane is dependent on the length and height of the above wires. Relevant compact formulae for determining mesh boundaries are deduced, and a procedure of general mesh generation is also given. A numerical example is presented, and a validation check is accomplished, showing that the approach leads to a significant reduction in unknowns and thus computation time and consumed memories, while preserving the sufficient precision. This approach is especially useful for modeling the electromagnetic coupling of wires and reference ground, and it may also be beneficial for other equivalent circuit modeling techniques.
The influence of semi-planar chiral metamaterial (CMM) structures on the important characteristics of circularly polarized (CP) antennas is investigated in this paper. Based on this idea, CP planar two-arm Archimedean spiral (ARSPL) antenna and helical antenna are designed and the effects of chiral covers on their gain (or directivity), axial-ratio (AR), and return loss are considered. The results demonstrate that this method is greatly effective and the addition of a semi-planar CMM cover at an optimized distance over the CP antenna, significantly improves its gain and axial ratio.
The plasma sheath communication blackout issue for hypersonic or reentry vehicles is addressed from a channel characteristic perspective. Different from previous research, this paper emphasizes the importance of plasma sheath channel in the study of plasma communication blackout, and the discussion on transmission and phase shift characteristic of plasma sheath channel and their effect on communication performance was made with detail. A mathematical plasma sheath channel model is proposed and following the roadmap about how to obtain channel characteristic parameter is given. Flow field simulation of a blunt conical body physical was made, and the electron density and collision frequency profile got from flow field result under different incident angle at Mach 10-20 are presented thoroughly. The performance for QPSK based communication system under the established plasma channel is evaluated finally. It is indicated in our research that channel attenuation feature variation regularity is consistent with that of incident wave or Mach number, but the phase shift variation regularity with incident frequency or Mach number appears fall into chaos because of multiple 360 degree removal of original phase shift from communication view and complicated ratio relationships among incident wave, plasma frequency and collision frequency. Communication simulations result show that bit error rate agree with phase shift chaos well and phase shift exert large influence on present typical racking, telemetry, and command system. Some useful implications obtained from this study to improve communication performance include high frequency, high power and further rapid acquisition/tracing phase-locked loop compensating large phase shift.
In this paper, a modified iterative fourier technique (MIFT) for thinning uniformly spaced linear arrays featuring a minimum sidelobe level as well as narrow beam is presented. Since IFT is a thinning procedure which has to be performed many trial times with different initial element distributions to get the optimum solution, it is, to some extent, time consuming. Moreover, in each trial of IFT, the number of iterations is usually low, which makes the method tend to be trapped in local solution even with a large number of trials. Therefore, the similar procedures for both MIFT and IFT are to derive the element excitations from the prescribed array factor using successive forward and backward Fourier transforms, and array thinning is accomplished by setting the amplitudes of a predetermined number of the largest element excitations to unity while the others to zero during each iteration cycle. Furthermore, in MIFT, based on the idea of gradual thinning which is inspired by perturbation theory, an adaptively changed fill factor is proposed to modify IFT with the purpose of accelerating computational speed and facilitating convergence. The immediate result caused by this modified fill factor can be embodied in two points. One point is that unlike the random number of iterations contained in different trials of IFT, the number of iterations in all trials of MIFT is a fixed value and only predetermined by the array inherent features (symmetrical or asymmetrical) and fill factor. Therefore, sufficient iterations are ensured in each trial to effectively help the algorithm avoid trapping. The other point is that when MIFT is performed, the array elements are gradually truncated, which maintains the most useful element excitations while maximally excludes the bad excitations, so that the optimum solution could be obtained through only a small number of trials and thereby substantially save computational cost. The effectiveness of MIFT will be demonstrated for various linear arrays and compared with the published reports.
This work presents a novel approach in building a multidimensional approximator which is used as a linear operator for mapping the vector of detuned filter characteristic to the vector of deviations of tuning elements. This has been done for the purpose of using it in postproduction filter tuning algorithm. With the use of collected sets of deviations of tuning elements and filter characteristics corresponding to them, the least squares method (LSM) is applied to determine the matrix which realizes the linear mapping between these vectors. The matrix found in this method approximates the vectors of both spaces (filter characteristics and corresponding deviations of tuning elements). In tuning process this matrix is used to determine the vector of tuning element deviations for a given detuned filter characteristic read from Vector Network Analyzer. To increase the ``quality'' of linear operator filter characteristics are transformed with the use of Karhunen-Loeve transform (Principal Component Analysis). In contrast to non-linear artificial intelligence approximators used in filter tuning and published to-date, this method does not require a time-consuming training process. Filter tuning experiments have been performed and proved the correctness of the presented approach.
The composite backscattering of the ship model on sea surface is investigated with the spilling breaking waves and ship bow waves. The spilling breakers are approximately modeled with the wedge-like waves, and the ship bow waves are simulated based on the Kelvin model. With the modified four-path model, each scattering component is evaluated with the high frequency approximation methods for the total composite scattering. Due to the volume scattering, the composite scattering at large incidence angles is strongly enhanced by the non-Bragg scattering. The relationship of the composite scattering and the ship motion is analyzed. The numerical results of sea surface scattering agree with the measured data well, and the complex physical mechanism of the low-grazing-angle composite scattering is explicitly evaluated in this paper.
According to the uniqueness theorem, the far field radiation pattern of radiators such as antennas can be determined from the measured tangential electric or magnetic field components over an arbitrary Huygens' surface enclosing the radiator. In this paper, a method using the spherical electric field measurement is developed to calculate the far field radiation. Following the Schelkunoff's field equivalence principle, a spherical region surrounding the radiator is assumed and its internal space is filled up with the perfect electric conductor (PEC). The radiated field from the Huygens' equivalent electric current is zero. Referring to the Ohm-Rayleigh method and the scattering wave superposition, the dyadic Green's function (DGF) with the presence of a PEC sphere is expanded by a series of spherical vector wave functions. Based on the DGF and the measured tangential electric field, the radiation behavior of the radiator can be directly predicted without involving the uncertainty from the inverse process. The robustness and accuracy of the proposed method are verified through several canonical antenna benchmarks.
A novel perturbation technique is formulated that enables the efficient calculation of current on surfaces undergoing time-varying mechanical deformations. The technique computes the current on the perturbed surface using as its starting point the solution for a related static case. This is initially derived using a standard analytical or numerical technique. The key advantage of this approach is that only an initial (computationally expensive) electromagnetic characterisation of the static problem is required. The surface current perturbation terms (and hence the radiated fields) are then directly computed from the static problem with a very low computational overhead.
The electromagnetic radiation of a handset antenna to a human head model is rigorously analyzed by a new hybrid approach. In the analysis, human head is modeled by a double layered prolate spheroid with complex permittivity. A hybrid Null Field Method/Method of Moments (NFM/MoM) approach is proposed for the first time. The method is general and capable of dealing with multiple scatterers and radiators. By means of the hybrid approach, the NFM is used to model the scattering problem of the head model, and the MoM is applied to a handset antenna. The electromagnetic coupling between the head model and an antenna is taken into account by a fast convergent iteration process. Numerical results of electric field near and inside the head model and the input impedance of the antenna are calculated by the proposed hybrid approach and commercial full wave EM software. Very good agreement is obtained, which demonstrates the accuracy and efficiency of the proposed approach.
Redundant flux-switching permanent-magnet (R-FSPM) motor is a new fault-tolerant machine having PMs in the stator, offering high efficiency, high reliability, and robust structure. This paper proposes two remedial control strategies for fault-tolerant operations of the R-FSPM motor drive in the single-channel (SC) mode. First, by doubling the healthy-channel currents, the reduced torque due to one channel loss can be remedied, the so-called remedial brushless AC (BLAC) operation mode. Second, by injecting harmonic current (IHC) considering harmonic back-EMF effect, the reduced torque can also be smoothly remedied, the so-called remedial IHC operation mode. Finally, both of the proposed remedial control strategies are verified by co-simulation and experimentation, hence confirming the validity of the proposed fault-tolerant R-FSPM motor drive.
This article is devoted to the construction and investigation of a class of polarization-invariant directional cloaks by concatenation of cloaking medium components via transformation optics. It improves the construction of the first polarization-invariant directional cloak, introduced by Agarwal et al. [1]. The main ingredient is to construct a capsuloid transformed metamaterial consisting of an lp-cylindrical transformation map and two half lp--spherical transformation maps. Numerical investigation is carried out to test the performances of the cloaks under different polarized incoming waves. A salient feature of our cloaks is compact-sizedness, namely the geometrical size is no longer dependent on the regularization parameter ρ under the non-uniform map. In particular, we study the cloaking effect with respect to the regularization parameter ρ and the incident direction.
This study respectively uses two optimizers, iterative Taguchi's method and particle swarm optimization, combined with the method of moments to optimize a logotype planar antenna for multiband applications. The proposed antenna consists of four metal letters, NCNU, which is the abbreviation of the authors' university name. This antenna can be used for university logo or advertisement applications. The antenna also serves as an example to compare the optimization performance of these two optimizers. Optimization results show that Taguchi's method achieves much better optimization performance than particle swarm optimization. This study also investigates the electromagnetic characteristics of the proposed antenna by parametric study using simulation. The presented optimization methods could be applied to designing similar logotype antennas.
Three notched bands are generated, at selected frequencies, in an extremely wideband base antenna to support multiple communication systems while avoiding inference from other existing narrowband systems. The design of a fully printed extremely wideband antenna and creating triple band-notched functions are addressed in this paper. Measurements demonstrate that the proposed printed base antenna has an extremely wide 2:1 VSWR bandwidth from 0.72 GHz, to 25 GHz with a ratio bandwidth of 34:1. The antenna has a simple structure and can be fabricated at low cost for multi-band and wideband wireless communication devices. Besides, this paper presents a technique to form three notched bands within the operating frequency range of the base antenna. By introducing a half-wavelength U-shaped defected ground structure (DGS) and a pair of quarter-wavelength open arc-shaped slots to the radiating patch, three notched bands are created to prevent interference from WLAN (2.4-2.484 GHz and 5.15-5.85 GHz) systems and downlinks of X-band satellite communication (7.25-7.75 GHz) systems.
A two-layer dual-waveguide probe measurement geometry is proposed to nondestructively measure the complex permittivity and permeability of planar materials. The new measurement structure consists of two rectangular waveguides attached to a PEC flange plate that is placed against the material under test, followed by a known material layer backed by a PEC. The purpose for this new measurement geometry is to improve the permittivity results obtained using the existing dual-waveguide probe geometries, namely, the PEC-backed and free-space-backed geometries, by permitting a larger electric field into the material under test and increasing the field coupling between the two rectangular waveguide apertures. The theoretical development of the technique is presented extending the existing single-layer PEC-backed method to the proposed two-layer dual-waveguide probe method. The new measurement structure is theoretically analyzed by replacing the waveguide apertures with equivalent magnetic currents as stipulated by Love's equivalence theorem. Making use of the magnetic-current-excited two-layer parallel-plate Green's function and enforcing the continuity of the transverse magnetic fields over the waveguide apertures results in a system of coupled magnetic field integral equations. These coupled magnetic field integral equations are then solved for the theoretical reflection and transmission coefficients using the Method of Moments. The desired complex permittivity and permeability of the material under test are found by minimizing the root-mean-square difference between the theoretical and measured reflection and transmission coefficients, i.e., numerical inversion. Last, experimental results utilizing the new two-layer technique are presented for two magnetic shielding materials and subsequently compared to the existing PEC-backed and free-space-backed dual-waveguide probe geometries.
The shooting and bouncing rays (SBR) method has been widely used to predict the radar cross section (RCS) of electrically large and complex targets. SBR computation time rapidly increases as the size and the complexity of a target increase. The angular division algorithm (ADA) can be applied to reduce the number of intersection tests in SBR, which facilitates faster RCS prediction. However, ADA has an error in its table construction step, resulting in incorrect prediction for multiple scattered fields. In this paper, the error is described, and the modified ADA (MADA) is proposed to correct the error and to enhance accuracy. Numerical results show that MADA can achieve good RCS prediction accuracy.
Efficiency often constitutes the main goal in the design of a power system because the minimization of power losses in the magnetic components implies better and safer working conditions. The primary source of losses in a magnetic power component is usually associated with the current driven by the wire, which ranges from low to medium frequencies. New power system tendencies involve increasing working frequencies in order to reduce the size of devices, thus reducing costs. However, optimal design procedures involve increasingly complex solutions for improving system performance. For instance, using litz-type multi-stranded wires which have an internal structure to uniformly share the current between electrically equivalent strands, reducing the total power losses in the windings. The power losses in multi-stranded wires are generally classified into conduction losses and proximity losses due to currents induced by a magnetic field external to the strand. Both sources of loss have usually been analyzed independently, assuming certain conditions in order to simplify the derivation of expressions for calculating the correct values. In this paper, a unified analysis is performed given that both power losses are originated by the electromagnetic fields arising from external sources where the wire is immersed applying the decomposition into transversal magnetic (TM) and transversal electric (TE) components. The classical power losses, the so called conduction and proximity losses, can be calculated considering the TM modes under certain conditions. In addition, a new proximity loss contribution emerges from the TE modes under similar conditions.
In this paper a theoretical investigation of electromagnetic field transmission through dielectric plano convex lens placed in chiral medium is analyzed. The chiral medium is described electromagnetically by the constitutive relations D = ε(E+γ∇×E) and B = μ(H+γ∇×H). Transmission's coefficients for chiral-dielectric and dielectric-chiral interfaces are derived analytically. The analytical field expressions for right circularly polarized (RCP) and left circularly polarized (LCP) waves are obtained using Maslov's method. Numerical computations are made for the field patterns around the caustic region using Mathcad software to observe the effect of chirality parameter.
A printed monopole ultra wideband (UWB) antenna with frequency band-notched characteristics is proposed and investigated. The antenna consists of a half-disk shaped structure combined with an inverted isosceles trapezoid structure. To achieve the frequency band notched characteristics, an open-ended thin slit with a length of about one quarter guided wavelength is inserted on the radiator. Multiple slits can be employed to realize multiple frequency band notched characteristics. To validate the concept, two prototypes are designed, fabricated and tested. The first is a single band notched UWB antenna whereas the second is a dual band notched UWB antenna. The simulated and measured results of both antennas are presented shown a reasonable agreement between them. The results also confirm the proposed UWB antenna design can achieve superior dual band-notch performance at desired frequency bands.
The design and analysis of a high-power wideband sheet-beam coupled-cavity traveling-wave tube operating at V-band is presented. The interaction circuit employs three-slot doubly periodic staggered-ladder coupled-cavity slow-wave structure, and a 5 : 1 aspect-ratio sheet electron beam is used to interact with the circuit. Combined with design of the well-matched input and output couplers, a 3-D particle-in-cell model of the sheet-beam coupled-cavity traveling-wave tube is constructed. The electromagnetic characteristics and the beam-wave interaction of the tube are investigated. From our calculations, this tube can produce saturated output power over 630 Watts ranging from 58 GHz to 64 GHz when the cathode voltage and beam current are set to 13.2 kV and 300 mA, respectively. The corresponding saturated gain and electron efficiency can reach over 32.5 dB and 15.9%. Compared with the circular beam devices, the designed sheet-beam TWT has absolute advantage in power capability, and also it is more competitive in bandwidth and electron efficiency.
A generalized equivalent cable bundle method (GECBM) is presented for modeling electromagnetic (EM) compatibility issues of complex cable bundle terminated in arbitrary loads. By introducing a new grouping criterion, complex cable bundles terminated in arbitrary loads can be reasonably simplified through a generalized equivalence procedure. The reduced cable bundle model can be used for modeling electromagnetic immunity, emission and crosstalk problems. The complexity and the computation time for the complete cable bundle modeling has been significantly reduced and fairly good precision is maintained. Numerical simulations are given to validate the efficiency and advantages of the method.
Design of high performance package interconnects using full-wave electromagnetic solvers is necessary due to increased operation speed, miniaturization and vertical 3D integration. Thus the segmented study and optimization is becoming inevitable for designers to improve the signal integrity of IC packaging. This paper addresses alternative methods and optimal designs on several components and structures for package electrical interconnects, including voiding technique, padless via implementation, spiral micro-via stacking and signal/ground layout pin patterns. The simulation results have been presented to demonstrate the improvements of optimized schemes. These methodologies could be treated as handy references and general guidelines applicable to different package designs and could result in significant improvements of overall package signal integrity performance.
Submit
