This paper proposes a newly designed compact coplanar-waveguide-fed wideband circularly polarized (CP) printed square slot antenna (PSSA), in the square slot of which are a halberd-shaped feeding signal line and a square ring patch. By placing a specially designed metal reflector behind the bidirectional CP PSSA, one can obtain unidirectional CP patterns with a associated 3-dB axial-ratio bandwidth (ARBW) almost the same as that of the bidirectional antenna. The bidirectional L- and S-band PSSAs designed on FR4 substrates have 3-dB ARBWs as large as 25.3% and 29.1%, respectively. For the L-band antennas, the unidirectional design yields a 3-dB ARBW of 25.7% and a gain of about 3 dB higher than that of the bidirectional counterpart. In all these 3-dB axial-ratio bands, impedance matching with VSWR ≤ 2 is also achieved. Most importantly, the design concepts, procedures, and rules for the proposed antenna are presented in detail.
A compact wideband dual-frequency microstrip antenna is proposed in this paper. By employing an offset microstrip-fed line and a strip close to the radiating edges in the circular slot patch, an antenna operating at dual frequency with the impedance bandwidth of 26.2% and 22.2% respectively is presented. By attaching a strip to the radiating edges opposite to the microstrip-fed line, this alters the current distribution and radiation on the antenna at the second resonant frequency. The second frequency is also tunable by varying the lengths of the microstrip-fed line. It is demonstrated that the proposed antenna covers the widebands of UHF and microwave for RFID application. A good agreement is obtained between the simulated and experimental results.
In this paper, we propose a simplified particle probability hypothesis density (PHD) filter and its hardware implementation for multiple-target tracking (MTT). In the proposed algorithm, the update step of particle PHD filter is simplified and the time-varying number of measurements is arranged in combination series/parallel mode. This may result in fixed hardware architecture and therefore present a convenient hardware implementation of particle PHD filter. Simulation results indicate that for the MTT problems, this proposed simplified algorithm shows similar performance with the standard particle PHD filter but has faster processing rate. Experiment study shows that the proposed simplified algorithm can be efficiently implemented in hardware and can effectively solve the MTT problems.
In the final step of any filter design process, the desired center frequency, coupling factor and external quality factor (Qext) are used to determine the physical parameters of the filter. Although in the most cases the physical dimensions of a single resonator for a given center frequency are determined using exact analytical or simple approximate equations, usually such simple equations cannot be found to easily relate the required coupling factor and Qext to the physical parameters of the filter. Analytical calculation of coupling factor and Qext versus dimensions are usually complicated due to the geometrical complexities or in some cases such as microstrip resonators due to the lack of exact solution for the field distribution. Therefore coupling factor and Qext of various kinds of resonators, especially microstrip resonators, are related to the physical parameters of the structure by the use of time consuming full wave simulations. In this paper a surprisingly fast and completely general approach based on a soft computing pattern-based processing technique, called active learning method (ALM) is proposed to overcome the time consuming process of coupling factor and Qext determination. At first the ALM technique and the steps of modeling are generally described, then as an example and in order to show the ability of the method this modeling approach is implemented to model the coupling factor and Qext surfaces of microstrip open-loop resonators versus physical parameters of the structure. Using the ALM-based extracted surfaces for coupling factor and Qext, two four pole Chebychev bandpass filters are designed and fabricated. Good agreement between the measured and simulated results validates the accuracy of the proposed approach.
A convergence study of a non-standard Schwarz domain decomposition method for finite element mesh truncation in electromagnetics is carried out. The original infinite domain is divided into two overlapping domains. The interior finite domain is modeled by finite elements and the exterior infinite domain by an integral equation representation of the field. A numerical study of the spectrum of the iteration matrix for non-convex mesh truncation boundaries is performed. The projection of the error between two consecutive iterations onto the eigenvector space of the iteration matrix is performed. The numerical results explain the observed convergence behavior of the Schwarz iterations.
In this paper, we propose several array topologies to achieve good power-combining characteristics for the open slot antenna. By utilizing an appropriate feeding structure and injecting in-phase or out-of-phase signals, power-combining radiation patterns can be derived. Simulated surface current distributions of several antenna structures are presented to explain radiation mechanism. From the results of radiation performance, the advantages of gain enhancement and pattern reconfiguration are shown. By varying the phase difference of two injected signals of the open slot antenna array, two-dimensional beam-scanning radiation patterns are successfully demonstrated.
In this paper we present the three-dimensional finite element time domain model of the human eye exposed to pulsed holmium: YAG laser radiation used in thermokeratoplasty procedure. The model is based on the Pennes' bioheat transfer equation and takes into account the focusing action of the lens. The absorption of laser energy inside the eye tissues is modeled using the Lambert-Beer's law. Model takes into account the pulse temporal profile. The maximum temperature values obtained from steady state and transient analysis are compared against those reported from other papers. Finally, sensitivity analysis of several parameters on the calculated temperature field is carried out.
A fast method for electromagnetic imaging from monostatic full rotational near-field scattering is proposed in this paper. It is based on circular spectrum theory which exploits the Fourier decomposition of the targets distribution instead of point by point imaging in earlier works. The novelty of the proposed method is that it simplifies the relationship between the spatial frequency domain and the scattering field. The near-field scattering is analyzed by expanding the distance to Taylor series at the centre of the targets zone. The near-field focus function is then transformed to spatial frequency domain and evaluated by the method of stationary phase. The imaging result is given by two-dimensional inverse Fourier transformation from spatial frequency domain of targets. The proposed method is validated by comparing the simulation results of distributed targets with the tomographic imaging. The dynamic range of imaging result is derived by distributed targets with different reflection coefficient. Furthermore, the experiment is also conducted in microwave chamber at Ku band with target placed on the turntable.
Radome has strong effects on the radiation performances of the antenna in millimeter wave band. In this paper, the aperture integration-surface integration (AI-SI) method is adopted to analyze the electrically large antenna-radome system. The fast multipole method (FMM) is proposed to accelerate the aperture integration and inner surface integration in the AI-SI method. An electrically large antenna-radome system at W band is analyzed and measured. The radiation patterns of the system calculated using the AI-SI method with and without the fast multipole acceleration and the measured patterns are compared. The calculated patterns agree very well with each other, and both have the same agreement with the experimental results. However, the computational time of the proposed analysis with the fast multipole acceleration is reduced significantly.
A novel approach for the design and optimization of spherical lens antennas (SLAs) including practical feed model (PFM) is proposed. The vector spherical wave function expansions (VSWE) combined with differential evolution (DE) algorithm is adopted for the optimal design of SLAs. Moreover, the near-field aperture distributions of a Ku band dielectric loaded horn feed and a Ka band corrugated horn feed were obtained using the full wave simulation and were then taken into account in the DE optimization. The performances of the optimized 2-layer design are compared with previous works, higher directivity is obtained. Additionally, the radiation characteristics of an optimized SLA are presented, and numerical results of a 650 mm diameter 2-layer hemispherical lens antenna (HLA) with ground plane are compared to the experimental results, and good agreements are obtained. An investigation of the influence of the various lens-to-feed distances as well as aperture sizes of SLA on the aperture efficiency for a 2-layer design is also proposed.
There are many applications of beam quality and beam shape in turbulent atmosphere. Because M2 factor and kurtosis parameters are often used to descripe beam quality and intensity flatness, the evolution of these two parameters of Hermite-Gaussian beam in turbulent atmosphere have been studied in both theory and numerical calculation. Results show that the spectrum of refractive index fluctuations has a strong effect on these two parameters. For some spectral models, these two parameters are very sensitive to some factors of turbulence. But for other spectral models, the factor is very insensitive to these factors. For example, when the exponent of the spectrum is very small, M2 factor is very insensitive to the outer scale of turbulence. But when the exponent of the spectrum is very large, the M2 factor is very insensitive to the inner scale. In addition, we also found that there are many differences between the kurtosis parameters under different conditions. For example, the kurtosis parameters may be very large during propagation. Namely, beam shape may be very sharp under some conditions. When the effects of turbulence is very large or very small, beam shape is very flat.
The permittivity of extra thin silk cloth is usually measured through some complex methods in the past. Here we propose a convenient and flexible method to measure the permittivity of extra thin silk cloth using resonant metamaterial structures. The metamaterial structures used here are symmetric split ring resonators (SRRs). The principle is that the resonant frequency of the SRRs is very sensitive to the permittivity of the surrounding medium. Therefore, the relative permittivity of an extra thin medium as silk cloth can be determined. Our experimental measurement shows that the relative permittivity of the silk cloth is 4.5. A piece of printing paper is also measured with a relative permeability of 1.4. The effectiveness of the method in determining the permittivity of a solid medium is very useful in future applications.
Conjugately characteristic-impedance transmission lines (CCITLs) are a class of transmission lines possessing conjugately characteristic impedances (Z0±) for waves propagating in the opposite direction. A typical Z0 uniform transmission line is a special case of CCITLs whose argument of Z0± is equal to 0o. This paper aims to generalize the CCITL system by demonstrating a theoretical study of CCITLs and their applications in the microwave transistor amplifier design. It is found that the bilinear transformation plays an important role in transforming circles in the reflection coefficient Г0-plane in the Z0 system to the Г-plane in the CCITL system. In addition, Meta-Smith charts, a graphical tool developed for solving problems in the CCITL system, are employed to design matching networks to achieve desired amplifier properties. Results show that stability regions on Meta-Smith charts can be determined, and source and load reflection coefficients can be selected properly to obtain desired operating power gain. In addition, an example shows that Meta-Smith charts offer a simple approach for matching network design using open-circuited single-stub shunt tuners.
A dual-core photonic crystal fiber (DC-PCF) is proposed, and bending characteristics of the DC-PCF are investigated. Two fiber cores are employed in the cross-section of the DC-PCF, which result in a mode coupling between the two fiber cores when the light propagates inside the DC-PCF. The mode coupling between two fiber cores of the DC-PCF is sensitive to the directional bending of the DC-PCF which essentially provides a method to achieve bending sensing. A DC-PCF-based bending sensor is proposed by injecting a broadband light into one fiber core of the DC-PCF on one side and detecting output spectrum from another fiber core of the DC-PCF on the other side. In our simulations, a parabola curve which shows the relationship between the wavelength shift of the transmission spectrum of the DC-PCF-based bending sensor and the bending curvature of the DC-PCF is presented.
In a previous paper, we proposed and tested a robust and efficient three-dimensional (3-D) subgridding algorithm for the FDTD solution method of the Maxwell's curl PDEs system. Its characteristic feature is the straight, non-recursive, embedding of Yee grids - refined by factors of 3, 5, 7 and even larger - within coarser ones. There, the algorithm's implementation was described with the traditional serial programming approach. In the present paper, we propose and test its parallel programming implementation. The goal is to make it suitable and efficient for large scale electromagnetic simulations.
A slotted-ground-plane meandered-slot resonator with multi-resonance characteristics and a compact lowpass filter (LPF) by using the resonator are demonstrated in this paper. The meandered slot provides a wideband resonator with low insertion loss and very sharp cutoff frequency response. Unlike conventional design of cascading bandstop slotted-ground-plane resonators in the literature, the introduced LPF is presented, which consists of a modified-meander slot in the ground plane, a spurred C-like slot, and a uniform microstrip transmission line with constant characteristics impedance. Two rectangular-head slots, giving an increase in the inductance, are added at the two terminals of the meandered slot for purpose of frequency reduction. An arm aperture is embedded to form another resonant path so that an additional transmission zero could be generated. In order to increase rejection capability, the slot width of one section of the meandered-slot resonator is widened. Meanwhile, a C-like slot with a spur slit is also etched inside the meandered slot to improve rejection performance. The measured insertion loss at a passband is below 0.7 dB, and the rejection band over 20 dB is from 2.9 to 12.0 GHz.
Vivaldi antennas have broad applications in real practice due to the ultra wideband properties. However, their gain and directivity are relatively low. In this paper, a new method is presented to improve the gain and directivity of Vivaldi antennas in a broad band using inhomogeneous and anisotropic (IA) zero-index metamaterials (ZIM). ZIM have the ability to enhance the antenna directivity; anisotropic ZIM with only one component of the permittivity or permeability tensor approaching to zero can make impedance match to improve the radiation efficiency; and IA-ZIM can broaden the frequency bandwidth. Single- and multiple-layered planar IA-ZIM have been analyzed, designed, and fabricated, which can be embedded into the original Vivaldi antenna smoothly and compactly. The IA-ZIM-based Vivaldi antennas have good features of high gain, high directivity, low return loss, and broad bandwidth. Compared to the original Vivaldi antenna, the measurement results show that the gain has been increased by 3 dB and the half-power beam width has been decreased by 20 degrees with the reflection coefficient less than -10 dB from 9.5 GHz to 12.5 GHz after using IA-ZIM.
A computational technique is presented for efficient and accurate time-domain analysis of multiport waveguide structures with arbitrary metallic and dielectric discontinuities using a higher order finite element method (FEM) in the frequency domain. It is demonstrated that with a highly efficient and appropriately designed frequency-domain FEM solver, it is possible to obtain extremely fast and accurate time-domain solutions of microwave passive structures performing computations in the frequency domain along with the discrete Fourier transform (DFT) and its inverse (IDFT). The technique is a higher order large domain Galerkin-type FEM for 3-D analysis of waveguide structures with discontinuities implementing curl-conforming hierarchical polynomial vector basis functions in conjunction with Lagrange-type curved hexahedral finite elements and a simple single-mode boundary condition, coupled with standard DFT and IDFT algorithms. The examples demonstrate excellent numerical properties of the technique, which appears to be the first time-from-frequency-domain FEM solver, primarily due to (i) very small total numbers of unknowns in higher order solutions, (ii) great modeling flexibility using large (homogeneous and continuously inhomogeneous) finite elements, and (iii) extremely fast multifrequency FEM analysis (the global FEM matrix is filled only once and then reused for every subsequent frequency point) needed for the inverse Fourier transform.
A RF directional modulation technique using a switched antenna array is proposed for communication and direction-finding applications. The main idea is that a baseband modulation signal is transmitted by the switched antenna array. The phase center of the transmit signal is moved by the feeding line of each element from the left to the right. In this way, the data information and Doppler frequency shift information are modulated into a transmit signal constellation simultaneously. Therefore, this constellation is a scrambled constellation compared with traditional baseband modulation signal, which varies with the azimuth angle information of the receiver. For the receiver with a single antenna, a differential correlation algorithm is employed to demodulate the data information, and an azimuth angle estimation algorithm is also developed to extract the azimuth angle information from this scrambled constellation. Simulation results show that this RF directional modulation technique offers a comprehensive scheme for communication and direction-finding from the point view of RF modulation technique.
The imaging quality of tomography SAR is limited by the low number of flight tracks and their non-uniform distribution. In this paper, a new 3-D imaging algorithm is proposed for tomography SAR based on the improved interpolated array transform. The key point of the proposed algorithm is the introduction of the projection technique into the interpolated array transform, which can reduce the energy of the interference signal and improve the imaging quality. Performance analysis under different scenarios is carried out via the simulations. And the results demonstrate that the sidelobe performance can be significantly improved by the proposed algorithm.
Fourier transform of discontinuous functions are often encountered in computational electromagnetics. A highly accurate, fast conformal Fourier transform (CFT) algorithm is proposed to evaluate the finite Fourier transform of 2D discontinuous functions. A curved triangular mesh combined with curvilinear coordinate transformation is adopted to flexibly model an arbitrary shape of the discontinuity boundary. This enables us to take full advantages of high order interpolation and Gaussian quadrature methods to achieve highly accurate Fourier integration results with a low sampling density and small computation time. The complexity of the proposed algorithm is similar to the traditional 2D fast Fourier transform algorithm, but with orders of magnitude higher accuracy. Numerical examples illustrate the excellent performance of the proposed CFT method.
In this paper, a novel longitudinally magnetized cylindrical ferrite coupled line (CFCL) junction is proposed. In comparison to planar ferrite coupled line (FCL) configurations, which are well known in literature, in such structure the higher gyromagnetic coupling occurs. This allows to obtain the required in FCL devices Faraday rotation angle π/4 for the ferrite with shorter length and lower value of magnetization. As a result the total insertion losses in the ferrite section can be reduced using the proposed topology. In the analysis of the proposed CFCL junction a hybrid technique combining method of moments and coupled mode method (MoM/CMM) is applied. The results are compared with the ones obtained from commercial software HFSS and a good agreement is obtained.
This paper presents a switched-beam antenna using circumferential-slot on a concentric sectoral cylindrical cavity excited by coupling slots to operate at 5.8 GHz. The advantages of this antenna are conformal structure, high directivity and capable of switched-beam pattern in six directions. The antenna design starts from a single sector which is capable of switching between radiating and non-radiating modes. The L-shaped coupling slots are proposed to accommodate the switching circuit. Each RF switch is made of two PIN diodes connected in a reverse series connection and placed across the slot at the appropriate location. Subsequently, the exciting probe is designed for matching TM01 mode of the circular waveguide. The measured results of the proposed antenna give a gain of 7 dBi and |S11| less than -20 dB at 5.8 GHz. This antenna is suitable for base station applications that require the switched-beam pattern in the azimuthal plane.
This study focuses on the evaluation of the performance of a rectangular waveguide for deep hyperthermia when different antennas are used. Although there are several models of hyperthermia applicators, there are no studies of the advantages of employing different antennas for waveguides used in deep seated tumor treatments. Monopole antennas are the most used radiating elements inside waveguides. Here, the modeling of a monopole and two new proposed antennas, inverted T and plate, in order to find their optimal performance is presented. Parameters like output power, SWR and transmission coefficient generated for each modeled antenna were calculated by using the finite element method. The antennas with the best performance were selected in order to model an applicator-phantom system, which was used to calculate the temperature distributions generated inside the muscle phantom. The models were based on Maxwell and bioheat equations. Finally, thermal distributions were obtained and compared. The results indicate that the plate antenna generated a better focusing. The SWR obtained was 1.25, the output power was 54.71 W of 66 W applied, and the 42°C isotherm had a size of 2 cm x 2 cm.
In the paper, an Illuminating Modes concept is introduced in order to find microstrip antenna parameters - resonant frequency, resonant resistance and radiation pattern. The concept is based on illuminating the rectangular patch by a single normally-incident plane wave. It results in the surface current density induced on the patch which is found by means of two-dimensional Spectral Domain Approach. Then, the resonant frequency, the quality factor, the resonant resistance and the radiation pattern of the analysed antenna are found. Application of Illuminating Mode concept in Spectral Domain Approach effects in analysis simplification and less time consuming calculations with no waste of the accuracy. Exemplary results for several kinds of radiators are presented, showing satisfactory level of agreement with published data.
This paper presents a two-stage optimization method for accurately extracting the coupling matrix (CM) and the unloaded quality factor (unloaded Q) of each resonator from the measured (or simulated) S-parameters of lossy cross-coupled resonator bandpass filters. The method can be used in computer-aided tuning (CAT) of microwave filters to accelerate filter design and physical realization. In our method, the Cauchy method is employed for determining characteristic polynomials of the S-parameters in the normalized low-pass frequency domain, and the CM and unloaded Q are extracted by two-stage optimization method using genetic algorithm. With respect to the previous methods available in the literatures, the proposed method allows the CM extraction of the filter with source-load coupling. Moreover, the accuracy and robustness of the method can be improved due to the usage of the second stage optimization. The proposed method is applied to the diagnosis of a general coupled resonator filter with/without source-load coupling.
A one-dimensional electromagnetic bandgap (1-D EBG) ground plane was designed and characterized. The 1-D EBG ground plane, composed of metal patches, metal lines, and a ground plane, has in-phase reflection characteristics when the polarization of the incident electromagnetic waves is parallel to the direction of the EBG unit-cell array. The proposed 1-D EBG ground plane was applied to the design of low-profile directive dipole antennas. The radiators of the designed antennas could be placed very close to the 1-D EBG ground plane without noticeable performance degradation of the antennas. In particular, the dipole antenna designed with the 1-D EBG ground plane and directors has higher directivity and a better F-B (front-to-back) ratio as compared to a conventional dipole antenna backed with a normal ground plane.
In this paper, tunable single-negative (TSNG) metamaterials based on microstrip with varactor diodes loading are investigated. By tuning the external voltage, our structure can provide either an epsilon-negative or a mu-negative band gap, with varying gap width (the ratio of bandwidth to center frequency can be from 0 to over 100%) and depth (from 0 dB to about -30 dB). Moreover, the tunneling mode in a heterostructure constructed by epsilon-negative and TSNG metamaterials is also studied. The results show that its transmission, Q-factor, and electromagnetic localization can also be controlled conveniently. All these properties make our structure promising to be utilized as a practical switching device, or a suitable platform for the study of nonlinear effect in metamaterials.
A method to enlarge the omnidirectional photonic bandgaps (PBGs) has been presented in the one-dimensional photonic crystals by sandwiching a superconductor layer between two dielectric materials to form a one-dimensional ternary periodic structure. The angle- and thickness-dependence of these PBGs have been investigated in detail, and then the thermally-tunability of these omnidirectional PBGs by controlling external temperature of the superconductor is discussed. It is shown that these omnidirectional PBGs can be extended markedly in the one-dimensional ternary photonic crystal and the gap width or the wavelength range can also be tuned by varying external temperature.
In this work, a novel multi-carrier Tx-Rx system based on rationally synchronized oscillators to be used in RF-source localization applications is presented. The Tx subsystem is composed by two rationally synchronized oscillators, with different operation frequency, which share the reference signal. This signal is transmitted together with the one generated by the oscillators. In the Rx subsystem, the reference signal is provided by an oscillator which is synchronized with the received reference signal. According to the simulation results, with the proposed approach, the determination of the relative phase variation suffered by the transmitted signals, due to the propagation channel, can be achieved with an error less than 0.6o. It is also shown that the dynamic response of the system can be optimized by properly selecting the operation point of all oscillators.