The Unified Spectral Technique (UST) is a rigorous analytical approach for calculating power fluxes of any type of source and losses in multilayered dielectric structures of canonical geometries. This method is a reasonable addition to the eigenfunctions technique. An important advantage of the method is that the power fluxes are represented in an explicit form via their spectra, avoiding cumbersome calculations via field components. In this paper, this approach is specified for a case of planar multilayered structures, including those made of composite materials. Results of computations for the simplest types of radiators (electric and magnetic dipoles) in proximity of parallel-plane composite layers, comprised of a dielectric base and conducting inclusions with concentrations below and above percolation threshold, are analyzed.
This paper proposes a computationally efficient method for a two-dimensional direction of arrival estimation of multiple narrowband sources. We apply the MUSIC method which requires eigenvalues decomposition to the cross spectral matrix. This paper will employ two L-shape arrays that showed better performances than the one L-shape and the parallel shape arrays. In spite of its computational complexity, simulation results verify that the proposed subspace technique gives much better performance than the propagator method.
In this work, the performance of a microring add-drop filter is investigated using the generalized multipole technique. The complete scattering parameters of the structure are computed using an efficient port solver based on the generalized multipole technique, which avoids spurious reflections at the terminations. The scattering parameters of a number of structures are calculated and compared with those obtained using the FDTD and coupled-mode theory methods. The generalized multipole method can advantageously take dielectric losses of the microring into account. Moreover, the total power loss including radiation and the dielectric losses is computed for a microring add-drop filter, for the first time.
This paper starts with the characteristics and advantages of microwaves processing. The shortcomings of fixed frequency, typically at 2.45 GHz were also mentioned. On account of this, a newly developed variable frequency microwave (VFM) fabrication was mentioned and adopted in place of the fixed frequency process. Two cases of fixed frequency microwave processing of materials were described; the characteristics, pros and cons of each case was mentioned and commented. Two cases of processing materials using variable frequency microwave facility (VFMF) were mentioned; the advantages and limitations of each case were discussed. The microwave processing of materials provides improved mechanical, physical and electrical properties with much reduced processing time. Furthermore, variable frequency microwave processing is more superior to its fixed frequency counterpart except that the cost of the facilities of the former is much higher than the latter at this point in time but it appears that the price will drop in the coming ten years.
This paper presents parametric analysis of Flat Sandwich Multilayer Radome using Boundary Value Solution technique. The effect of variations in the characteristics of constituent layers of Radome on its microwave transmission properties has been studied. This work has relevance in development of Planar Array Radar Antennas especially for airborne platforms.
Planar metamaterials with spiral elements are suggested in this paper to support multiple left-handed (LH) modes. Compared with previously proposed split-loop metamaterial, spiral arrays are found to support hybrid TE and TM LH modes. Dispersion diagrams and field distributions are carried out to demonstrate the existence of the hybrid LH modes. Array with double-spiral elements can be viewed as a spiral split-loop array, which leads a very interesting dual-LH-band feature. It can be explained as a combination of spiral and split-ring arrays has similar mechanism with the multiband frequency selective surfaces (FSS), which have multiple resonators in a single unit cell. The two LH modes are TE and TM modes respectively. Validations of the multiple LH modes are presented by means of full-wave simulation using commercial software (Ansoft HFSS).
In this paper we propose a digital beamformer utilizing the radar integrator method of detection. In the receive mode the digitized radar returns weights are allocate on the such a way that the first pulse reflect a SUM pattern and the subsequent three pulses reflect DIFFERENCE pattern. The pulses on DIFFERENCE pattern are added to each other and the net signal subtracted from signal received in SUM pattern. This results in very narrow beam which shows narrow spatial resolution. The schematic is presented and the results are shown.
An analytical model of composites made of a dielectric base and randomly oriented metal inclusions in the form of nanorods is presented. This model is based on the generalized Maxwell Garnett (MG) mixing rule. In this model, the nanorod particles are modeled as prolate spheroids with a statistically normal distribution of their aspect ratios. It is shown that parameters of the distribution laws affect the frequency characteristics of the composites both at microwave and optical frequencies. The results of computations are represented.
This paper investigates broadband planar antennas that consist of a wide rectangular slot with various tuning stubs. The antennas are fed by coplanar waveguides. Wide slots containing a single tuning stub, V-shaped stubs, as well as inverted F-shaped stubs are investigated. Despite using a high dielectric constant substrate, the proposed antennas exhibit very broad bandwidth. They also have broadside bidirectional radiation. The radiation pattern stability with frequency for the various configurations is presented. One of the proposed configurations, the inverted F stub in a wide rectangular slot, produced very stable radiation patterns over its entire impedance bandwidth of about 40%. Also, an impedance bandwidth of 44% was obtained for the V-shaped stub in a rectangular slot. Simulations as well as experimental results are presented.
This study analyzes polarizability properties of spherically layered small inclusions that possess negative permittivity. Conditions for invisibility to external electric fields are derived. The complementary principle for two-dimensional scatterers is used to derive special properties of self-complementary inclusions. A singular behavior between the limits of invisibility and infinite response is underlined for a hollow circular shell. A similar,although not as drastic,phenomenon is shown to take place for the three-dimensional hollow sphere.
Metamaterials with small electrical size are more feasible to be described by the macroscopic parameters and treated as an effective homogenous media. By using geometric optimization, we experimentally realize a metamaterial composed of crankled S-ring resonator,whose electrical size is 2.5 times smaller than the conventional S-ring resonator. The overall effective capacitance of the unit structure is greatly increased when viewed from an equivalent circuit model point of view,so the resonant frequency is decreased, and the metamaterial works at a much longer wavelength regime. In addition,w e summarize two kinds of other methods that could be used to reduce the electrical size of the structures. Experimental and simulation results are presented,sho wing the effectiveness of these methods in the metamaterial homogenization.
An efficient metal-insulator-metal (MIM) capacitor simple scalable model for use in monolithic-microwave integrated circuit (MMIC) design is presented in this paper. This model is based on transmission-line theory. Analytical expressions based on physical parameters have been given in detail. Nine different physical dimension capacitors are fabricated to verify the validity of the proposed model. A good agreement between measured result and simulated data is obtained.
This paper studies the performance appraisal of radiation performance of ultra low sidelobe level Active Phased Array Antennas in presence of Multilayer Flat Sandwich Radome. Further, the effect of errors introduced due to amplitude/phase quantisation and planarity of the array surface, on the radiation performance has been studied. Based on these errors, manufacturing tolerances of the Flat Sandwich Radome have been suggested to control the deterioration of radiation performance within tolerable limits. This work is expected to be useful in development/manufacturing of radomes for Active Phased Array Radars and similar applications where ultra low sidelobe levels are required to be maintained.
This paper presents an optimum design technique ofan asymmetric V-dipole antenna and it's a three-element Yagi-Uda array using Genetic Algorithm (GA). The optimization parameter for the V-dipole is the directivity and that for the Yagi-Uda array are the input impedance and directivity. The theoretical analysis has been done using a Moment-Method technique in a very simple step-by-step way, and subsequently the GA is applied for obtaining the optimized parameters. Comparative results are provided for 3-elements straight dipole Yagi and V-dipole Yagi array. Further, analysis for directivity with respect to included angle is given for the GA based optimization problem that gives an important aspect in the design of V-Yagi.
A kind of microstrip array double-antenna (MADA) and its corresponding radar front-end are presented in this paper. The double-antenna comprises two individual 4-patch arrays which are coplanar in a round substrate with 25mm diameter and are used as receiver antenna and transmitter antenna respectively in 36 GHz radar front-end. Both simulation and test results of the antenna are exhibited, which shows better isolation between two arrays below âˆ’42 dB in a wide band. Test results of radar front-end with MADA are also presented, from which we can see perfect performance the system has. With improvement of radar system, a more compact MADA with 18.6mm diameter is designed, fabricated and measured, which shows a good response.
This paper discusses the analysis of a novel two-segment rectangular dielectric resonator antenna (DRA) for broadening of the impedance bandwidth. In the proposed configuration, two rectangular dielectric sections are used which are separated by a metal plate. With this configuration, it is possible to excite two adjacent resonant frequencies. Utilizing the two-segment thin DRA and skillfully varying its aspect ratio, an appropriate structure is obtained that illustrates more than 76.8% impedance bandwidth (for S11>10 dB) at 3.32- 7.46 GHz frequency band.
In this paper, a new structure is proposed for microwave filters. This structure utilizes a waveguide filled by several dielectric layers. The relative electric permittivity and the length of the layers are optimally obtained using least mean square method. The usefulness of the proposed structure is verified using an example.
The focusing characteristics of 2D-Cylindrical Electromagnetic Band Gap (CEBG) structures constituted of metallic wires and with defects are analyzed numerically for directive antennas application. The introduction of defects into the periodic structures consists of removing one or multiple wires. The simulations were carried out with a Finite Difference Time Domain (FDTD) code, where the excitation is a line source and the CEBG structure is considered infinite in the vertical direction. Numerical results showing the effects of the number of cylindrical layers and of the number of defects are presented and discussed. These results allow to determine the structures giving best focusing performance and to obtain the frequency band for directive radiation.
Aclosed-form formula, the discrepancy parameter, which has been defined as the ratio of the modal expansion coefficients between the electromagnetic field obtained from the image approximation and the incident electromagnetic field, has been proposed for the evaluation of the validity of the image approximation in the electromagnetic wave propagation, i.e., Love's equivalence principle, and the electromagnetic wave scattering, i.e., the induction equivalent and the physical equivalent, in the cylindrical geometry. The discrepancy parameter is derived through two equivalent methods, i.e., the vector potential method through the cylindrical addition theorem and the dyadic Green's function method, for both the TE and TM cylindrical harmonics. The discrepancy parameter justifies the fact that the image approximation approaches the exact solution for the cylindrical surface of infinite radius. For the narrow-band field with limited spectral component in k space, the cylindrical modal expansion of the electromagnetic wave into the TE and TM cylindrical harmonics can be separated into the forward-propagating wave that propagates forward and the back-scattered wave that is back-scattered by the PEC surface, within the image approximation. The discrepancy parameter shows that the validity of the image approximation depends on the property of the incident field and the radius of the cylindrical surface, i.e., the narrow-band field and the surface of a large radius are in favor of the image approximation, which has also been confirmed by the numerical result.
In this paper, the higher order hierarchical basis functions are employed to solve the electric field integral equation for computing electromagnetic scattering from three-dimension bodies comprising both conducting and dielectric objects. In higher-order methods of moments (HO-MoM), the equivalent surface electric and magnetic currents are usually expanded by the same basis functions, which are not appropriate in our problem here. The pointwise orthogonal basis functions respectively for electric and magnetic currents are proposed in our improved HO-MoM. Quadrilateral patches are used in curvilinear geometry modeling since they result in the lowest number of unknowns. Numerical solution procedure is particularly analyzed, and numerical results are given for various structures and compared with other available data lastly.
In this paper we investigate the effect of replacing the ordinary rectangular microstripp atches in a linear antenna array with fractal patch elements. It is shown that using fractal patches substantially decreases the Mutual Coupling between elements. The effects of fractal type, spacing between elements, feed point location and number of parasitic elements on array performance has been studied.
This paper presents an icosahedron-based spherical antenna array for phase mode processing. In this topology, the interelement spacing is almost identical. This feature is useful for threedimensional beam scanning and for reducing the effects of mutual coupling. The use of directional elements in this array for wideband synthesis is discussed, and our results show that the use of such elements can overcome the limitations of rapid variations in the amplitude of the far-field mode over a wide frequency band and enable such array to synthesize wideband patterns.
A novel method is introduced to synthesize microstrip Nonuniform Transmission Lines (NTLs) for matching between two arbitrary complex frequency dependent impedances in a wideband or multi-band frequency range. First, stripwidth or the characteristic impedance function of the microstrip NTL is expanded in a truncated Fourier series. Then, the optimum values of the coefficients of the series are obtained through an optimization approach. The usefulness of the proposed method is verified using some examples.
In this paper, new circuit models are used to calculate the induced fields in biological media exposed to an incident plane wave in the two-dimensional cases. These models represent the induced fields in the medium using the lossy long transmission line model . The voltages and currents in the circuit model simulate the electric and magnetic fields in the medium. The response of the medium to the incident wave is represented by equivalent conduction and polarization current sources in the medium. These currents are used as the excitation sources in the circuit model from which the required induced fields are obtained. An accurate absorbing impedance boundary condition for open boundaries is used which considerably reduces the matrix dimensions. The validity of these models is tested in the problem of absorption of E- and H-waves by biological multilayered cylinders. Results are compared with available analytical and numerical solutions.