A new high gain wideband L-probe fed inverted EE-H shaped slotted (LEE-H) microstrip patch antenna is presented in this paper. The design adopts contemporary techniques; L-probe feeding, inverted patch structure with air-filled dielectric, and EE-H shaped patch. The integration of these techniques leads to a new patch antenna with a low profile as well as useful operational features, as the broadband and high gain. The measured result showed satisfactory performance with achievable impedance bandwidth of 21.15% at 10 dB return loss (VSWR ≤ 2) and a maximum gain of 9.5 dBi. The antenna exhibits stable radiation pattern in the entire operating band.
For the inverse synthetic aperture radar (ISAR) imaging of a target at a long range, range alignment using the existing polynomial method brings about poor results because the flight trajectory changes depending on the initial position, and the motion parameters, meaning the polynomial cannot fit the trajectory. This paper proposes an improved range alignment method that models the trajectory using a combination of a polynomial and Gaussian basis functions. Initial parameters of the polynomial and Gaussian basis functions are determined by fitting the proposed model to the center of mass curve of the range profile history using the least square curve-fitting algorithm, and the optimum value is found using particle swarm optimization. This method is computationally more efficient and preserves the image quality.
We have proposed a simple waveguide method for complex permittivity determination of dielectric materials which are not completely filling the entire sample holder. The method reconstructs the permittivity from measured reflection-only scattering parameters by a one-port vector network analyzer of two configurations of the sample holder. It not only eliminates the necessity of any knowledge of the location of the shifted sample inside its holder but also decreases measurement errors occurring with the presence of undesired air gaps, which seriously affect the measurement accuracy of transmission-only measurements, present between the sample and holder walls. Furthermore, the reconstruction of permittivity can be realized by any one-port vector network analyzer, which is less expensive than their two-port counterparts. Therefore, the proposed method is cost-effective. We have analyzed the accuracy of the proposed method and noted a good compromise between the reference data and measured values of permittivities of low-loss polyvinyl-chloride and polytetrafluoro−ethylene samples (less than 8 percent for dielectric constant and less than 15 percent for loss tangent values).
The resonant characteristic of frequency selective surfaces (FSSs) on in-plane biased ferrite substrates for the TE polarization is described. An approximate formula for evaluating the resonant frequency is presented. The tunable property of the resonant frequency of a dipole FSS is firstly demonstrated by the results obtained from the moment method (MM) and the waveguide simulator measurement. Then the approximate formula is validated by the MM as well as measured results already published in a previous paper. It is interesting to note that two separate resonances occur at any magnetic bias field, and both increase as the magnetic bias field increases. The fractional tuning range is investigated based on the approximate formula. The results show that it increases as the saturation magnetization increases and decreases as the center frequency increases.
Phase unwrapping is a key problem to generate digital elevation maps (DEMs) by synthetic aperture radar (SAR) interferometry. A lot of phase unwrapping algorithms have been proposed to solve this problem. However, in noisy region, many unwrapping algorithms are inoperative because of the denseness of residues. In this paper, we propose a path following phase unwrapping method, namely Residue-Pairing (RP) algorithm. The algorithm starts from residues, based on the aggregate of coordinates of each positive residues (or negative residues), to search the nearest opposite polar residue and connect them. Compared to the Goldstein's algorithm, the brunch cuts produced by this algorithm can effectively decrease their total length and contract the isolated region especially in noisy region. With raw data simulation, the results confirm the validity of RP algorithm in dense-residues region.
A dual-band multifunction hybrid antenna for carborne satellite communication relay system is presented in this paper. As a consequence of the radiation requirements, the proposed antenna consists of a left-hand circularly polarized (LHCP) microstrip patch and an omnidirectional biconical antenna with a conductor tube holding and radome. The LHCP microstrip antenna is used for satellite signal reception, and bionical antenna is used for relay communication transmission. A novel overmoded coaxial waveguide feed structure eliminates the interference between two feed ports. The proposed antenna has the advantages of robustness, low cost, and easy fabrication with conventional materials and printed circuit technology. An antenna prototype is fabricated to validate the design. Both the simulated and measured results are obtained with reasonable agreement.
This paper presents some improved analytical expressions of the magnetic field produced by arc-shaped permanent magnets whose polarization is radial with the amperian current model. First, we show that the radial component of the magnetic field produced by a ring permanent magnet whose polarization is radial can be expressed in terms of elliptic integrals. Such an expression is useful for optimization purposes. We also present a semi-analytical expression of the axial component produced by the same configuration. For this component, we discuss the terms that are difficult to integrate analytically and compare our expression with the one established by Furlani . In the second part of this paper, we use the amperian current model for calculating the magnetic field produced by a tile permanent magnet radially magnetized. This method was in fact still employed by Furlani for calculating the magnetic field produced by radially polarized cylinders. We show that it is possible to obtain a fully analytical expression of the radial component based on elliptic integrals. In addition, we show that the amperian current model allows us to obtain a fully analytical expression of the azimuthal component. All the expressions determined in this paper are compared with the ones established by Furlani or in previous works carried out by the authors.
A compact dual-band annular-ring slot antenna (ARSA) is proposed for use in 2.4/5 GHz wireless local-area networks (WLANs). With a meandered grounded strip embedded in the ring slot, three resonant modes were excited. With a pair of notches properly etched in the inner circular patch, the third resonant band was sufficiently lowered so that the second and third resonant bands are combined to form a wider upper operating band. If scaled to the same lower operating-band center frequency, the proposed ARSA measures only 53.6% the area of a conventional microstrip-line-fed ARSA. Measured and simulated results were found to agree reasonably well with each other.
Based on the use of micro electro-mechanical system (MEMS) switches this paper presents a composite right/left-handed (CRLH) transmission line (TL) with a reconfigurable behaviour. The design strategy here adopted consists on the use of metal-insulator-metal (MIM) capacitors and short-circuited stubs resulting in a very compact and monolithic CRLH unit cell well suited for phase shifter applications.
This paper addresses the sensor selection problem which is a very important issue where many sensors are available to track a target. In this problem, we need to select an appropriate group of sensors at each time to perform tracking in a wireless sensor network (WSN). As the theoretical tracking performance is bounded by posterior Cramer-Rao lower bound (PCRLB), it is used as a criterion to select sensors. Based on the PCRLB, sensor selection algorithms with and without sensing range constraint are developed. Without sensing range limit, exhaustive enumeration is first adopted to search all possible combinations for sensor selection. To reduce complexity of enumeration, second, we restrict the selected sensors to be within a fixed area in the WSN. With sensing range constraint, a circle will be drawn with the help of communication range for sensor selection. In a similar manner, two approaches, namely, selecting all sensors inside the circle or using enumeration to select sensors within the circle are presented. The effectiveness of the proposed methods is validated by computer simulation results in target tracking for WSNs.
Modern electronic products are increasingly based on high-speed, high-density circuitry operating at lower voltages. With such designs, the signal integrity (SI) in a poor printed circuit board layout is affected by noise and may become unstable. Crosstalk is a major source of noise that interferes with SI. Generally, crosstalk can be reduced by adding a guard trace between the victim and aggressor areas of the circuit. In addition, grounded vias can be added to the guard trace to help reduce crosstalk. Since a large number of grounded vias degrade the SI and reduce the flexibility of the circuit routing, we propose a method to calculate the optimal distance between grounded vias in the guard trace and determine the smallest number of vias required to achieve optimal performance in reducing crosstalk. We show by time-domain simulation that our method reduces the near-end crosstalk by 27.65% and the far-end crosstalk by more than 31.63% compared to the three-width rule. This is backed up by experimental results that show not only reductions of 34.49% and 37.55% for the near- and far-end crosstalk over time-domain, respectively, but also reductions of 2.1 dB and 3.3 dB for the near- and far-end crosstalk over the frequency-domain, respectively. Our results indicate that our method of optimal grounded vias has better performance than other methods.
An accurate and efficient formulation is presented for the electromagnetic analysis of dielectric waveguide gratings under plane-wave conical incidence. An arbitrary number of dielectric bars can be placed inside each one-dimension periodic cell, including the effect of dielectric losses. The reflectance of a dielectric waveguide grating under conical incidence is compared with theoretical results presented by other authors, finding a very good agreement. A single-layer reflection filter has been designed centered at λ0=1.5 μm whose spectral and angular responses are shown. For this structure, the effect of the asymmetry of the distribution of the refraction index in the reflectance has been analyzed, observing a splitting of the reflection peak around the design wavelength. Finally it is discussed the equivalence between a volume grating and a shallow surface-relief grating, providing two examples of designing prescriptions.
In this paper, we study the bistatic reflection and transmission properties of random rough surface with large slope and large height. Method of Moment (MOM) is used to solve the surface integral equations for 2D rough surface scattering problem. The modeled rough surfaces are similar to random rectangular grating, so that there are large slopes on the surface. The motivation of the study is to analyze scattering by sastrugi surface in Polar Regions. The ridges on the sastrugi surface have heights of about 20 cm. In microwave remote sensing of land at 5 GHz, 10 GHz, 19 GHz and 37 GHz, these heights are larger than wavelength. Next, we consider the scattering problem of the sastrugi rough surface over multi-layered snow. The bistatic reflection and transmission coefficients from MOM solutions are used as the boundary conditions for multi-layered radiative transfer equations. The radiative transfer equations are solved and the reflectivities are calculated. Numerical results are illustrated as a function of roughness and multi-layered parameters. We demonstrate that rough surface of sastugi, when interactions with layered media, causes increase in reflectivity and the decrease in emissivity. The increase of reflectivity can be attributed to the fact that rough surface with large slope facilitates large angle transmission. The large angle transmission results in increase of subsurface reflection and the possibility of total internal reflection in layered media below the rough surface.
We report fast and accurate simulations of metamaterial structures constructed with large numbers of unit cells containing split-ring resonators and thin wires. Scattering problems involving various metamaterial walls are formulated rigorously using the electric-field integral equation, discretized with the Rao-Wilton-Glisson basis functions. Resulting dense matrix equations are solved iteratively, where the matrix-vector multiplications are performed efficiently with the multilevel fast multipole algorithm. For rapid solutions at resonance frequencies, convergence of the iterations is accelerated by using robust preconditioning techniques, such as the sparse-approximate-inverse preconditioner. Without resorting to homogenization approximations and periodicity assumptions, we are able to obtain accurate solutions of realistic metamaterial problems discretized with millions of unknowns.
Ray-tracing exercise and full-wave analysis were performed to validate the performance of a type of cloak composed of isotropic metamaterials. It is shown that objects inside the 'folded region' of this cloak appear invisible to the incoming light from a ray tracing exercise, but exhibit magnified and shifted scattering under a plane wave illumination from a full wave analysis. Gaussian beams are introduced to resolve this interesting paradox resulted from these two methods. We show that at the time-harmonic state, small energy can be diffracted into the folded region and contribute to the resonant state even when the Gaussian beam is steered away from the cloak with an object inside. A scattering pattern identical to that scattered from the image of the object will be formed, which agrees well with the phenomenon in the plane wave incidence case.
μThe surface wave modes in the chiral negative refraction grounded slab waveguides in which the slab or cladding consists of chiral negative refraction metamaterial are investigated. The dispersion relations, electromagnetic fields, energy flow distribution and the total power of surface wave modes are presented. Some novel features have been found. The energy flow of surface wave mode is in opposite directions in the core and cladding. The total power is negative (corresponds to backward wave) in the grounded chiral negative refraction metamaterial slab waveguides.
This paper presents a radio wave propagation prediction method for low-rise buildings using 2-D aerial images taken from actual areas. The prediction procedure was done in three steps. Firstly, the images were classified in order to identify the objects by Color Temperature Properties with Maximum Likelihood Algorithm (CTP_MLA). The objects in the images consist of buildings, trees, roads, water and plain. These objects influence wave propagation highly. The MLA classification is a common supervised image segmentation technique in remote sensing domain. However it still needs human editing in case of classification errors. Secondly, the appropriate path loss models were selected to predict path loss. The original Xia path loss model was modified to include the effects of airy buildings and vegetation around the buildings. Finally, preliminary tests provide a better solution compared with measured path losses with the root mean square error (RMSE) and maximum relative error (MRE) of 3.47 and 0.16, respectively. Therefore, the positions for micro-cell base stations could be designed on a 2-D aerial map.
A new method called Expanded Cholesky Method (ECM) is proposed in this paper. The method can be used to decompose sparse symmetric non-positive-definite finite element (FEM) matrices. There are some advantages of the ECM, such as low storage, simplicity and easy parallelization. Based on the method, multifrontal (MF) algorithm is applied in non-positive-definite FEM computation. Numerical results show that the hybrid ECM/MF algorithm is stable and effective. In comparison with Generalized Minimal Residual Method (GMRES) in FEM electromagnetic computation, hybrid ECM/MF technology has distinct advantages in precision. The proposed method can be used to calculate a class of non-positive-definite electromagnetic problems.
The potential to implement microwave filters with special properties, by loading a waveguide with artificial Single Negative (SNG) or Double negative (DNG) materials was investigated. The SNG or DNG medium was structured with dielectric spherical particles of high permittivity embedded in a dielectric material of much smaller permittivity. Numerical analysis of the frequency response of the waveguide loaded with slabs of this type of composite dielectrics reveals that filtering performance, with attributes like very sharp attenuation at the bounds of frequency pass or stop band can be obtained. The central frequency as well as the bandwidth of the filtering can be controlled via the size and the dielectric constants of the particles, the dielectric constant of the hosting material and the size of the slab.
This paper proposes a hybrid methodology that combines an extended form of Finite-Deference Time-Domain (FDTD) method with Time Domain Physical Optics (TDPO) for analysis of 3-D scattering of combinative objects in complex electromagnetic compatibility (EMC) problems. Establishing a covariant formulation for FDTD, the extended algorithm introduces a parametric topology of accurate nonstandard schemes for the non-orthogonal div-curl problem and the suppression of lattice dispersion. For complex-combined objects including a small size (SS) and large size (LS) parts, using TDPO is an appropriate approach for coupling between two regions. Thus our technique solves the EMC complexity with the help of higher order FDTD (HOFDTD) and the combinatory structures by using of the TDPO. Numerical validation confirms the superiority of the proposed algorithm via realistic EMC applications.
A new microwave method based on calibration-independent measurements has been proposed for non-ambiguous complex permittivity determination of liquid materials. We have derived a function in terms of the first-reflection coefficient of the sample using raw complex scattering parameter measurements of three measurement configurations. We have verified the proposed method from measurements of two liquid test samples with the available reference data in the literature.
This paper presents a multiband slot antenna with modifying fractal geometry fed by coplanar waveguide (CPW) transmission line. The presented antenna has been designed by modifying an inner fractal patch of the antenna to operate at multiple resonant frequencies, which effectively supports the digital communication system (DCS 1.71-1.88 GHz), worldwide interoperability for microwave access (WiMAX 3.30 - 3.80 GHz), IMT advanced system or forth generation mobile communication system (3.40-4.2 GHz), and wireless local area network (WLAN 5.15 - 5.35 GHz). Manifestly, it has been found that the radiation patterns of the presented antenna are still similarly to the bidirectional radiation pattern at all operating frequencies. The properties of the antennas, for instance, return losses, radiation patterns and gain are determined via numerical simulation and measurement.
Due to the special structure of current carrying planar spiral coils, precise calculation of the forces between them is complicated and time-consuming. To overcome these problems, in this paper a new and fast method is proposed for calculation of the magnetic forces between planar spiral coils. The advantage of the proposed method is that just by having the external dimension of coils and their number of turns, the force between them at different distances and with different currents can be calculated. The results obtained by direct and proposed calculation methods show the efficiency of the latter in simplicity and calculation time. The precision of the proposed method has been confirmed by experimental tests done on constructed coils.
We are developing prototype free electron maser (FEM) that is compact, tuneable and efficient for potential industrial use. Therefore we define the characteristics for the construction of a novel X-band rectangular waveguide pre-bunched free electron maser (PFEM). Our device operates at 10 GHz and employs two rectangular waveguide cavities (one for velocity modulation and the other for energy extraction). The electron beam used in this experiment is produced by thermionic electron gun which can operate at 3 kV and up to 5 mA. The resonant cavity consists of a thin gap section of height 1.5 mm which reduces the beam energy required for beam wave interaction. The prototype design, engineering and construction process are reported in this paper.
In this paper, a time stepping two-dimensional FEM is performed for modeling and analysis of a IM with insulation failure inter-turn fault. FEM analysis is used for magnetic field calculation and the magnetic flux density and vector potential of machine is obtained for healthy and faulty cases. Comparing the magnetic flux distribution of healthy and faulty machines helps to detect the influence of turn fault. The machine parameters (self and mutual inductances) are obtained for IM with inter-turn fault. Finally, the FEM machine model is used for studying the machine under different fault condition. Study results including phases and fault currents express the behavior of machine with inter-turn faults. The symmetrical current components of IM with different fault severity are obtained by FE study and studied. The machine torque in healthy and faulty condition is also obtained and compared. The torque vibration increase upon to degree of fault.