The interaction of a helical antenna,moun ted on a mobile handset, with a human head phantom is investigated in this paper. Using the Genetic Algorithms (GA) technique combined with the Method of Moments (MoM), an optimization of the antenna structure is achieved regarding the input impedance at the operating frequency. The Finite Difference Time Domain (FDTD) method is then applied to simulate the handset's function in the close region of a spherical homogeneous and heterogeneous head phantom. A formula, based on an application of an existing model proposed by Kuster and Balzano for dipole antennas,pro vides a rather accurate prediction of the induced Specific Absorption Rate (SAR) values in the human head due to the radiating helical antenna. The concept of relating the SAR to the current on the antenna is used in this study to formulate the final expression. Moreover,using the theory of regression, the results of the calculated peak or average SAR are correlated with the distance between the antenna and phantom and with the standing wave ratio (SWR) at the antenna feed point. Thus,the conception that the SAR is indeed related to the antenna operational parameters is reinforced by the outcome of the current study.
Stacked microstrip antennas deserve special attention due to their advantageous properties like dual frequency operation and wide bandwidth. In the present communication a theoretical model for single stacked microstrip disc antenna is proposed using extended cavity model. The method of analysis by this model is easier and intuitive than the full wave analysis. Single stacked microstrip disc antenna with co-axial feed locations at different radial positions is analyzed with this model taking different ratios of patch sizes. Antenna properties like return loss, input impedance, gain and radiation efficiency are calculated with the proposed model different cases and compared with the simulated and experimental results. The results are in fairly good agreement.
In this paper we propose a new method to enhance the gain of rectangular waveguide antenna arrays using the double negative medium (DNG) structure composed of strip wires (SW) and split ring resonators (SRR). The electromagnetic parameters of the DNG structure are retrieved and the rectangular waveguide antennas with and without the DNG structure are studied using numerical simulation method. The simulation results show that the DNG structure can congregate the radiation energy when the index of refraction approximates zero,since that the gain of the antenna arrays is enhanced and the radiation performance of the antenna arrays is effectively improved. Far-field radiation patterns are measured, which indicate that this method is effective to enhance the gain.
In this paper an edge coupled microstrip coupler with defected ground structure is presented. A normally 7 dB coupler designed on Alumina substrate is converted into a 3 dB coupler by cutting single rectangular slot in the ground plane encompassing the two transmission lines. Other properties of backward wave coupler remain the same, except for a tighter coupling. With this method of design optimization, it will be possible to fabricate a 3 dB coupler in compact form without strain in fabrication process. The structure is analyzed considering magnetic and electric coupling between the two transmission lines. Simulation based studies show reasonable agreement between analytical results and corresponding simulation results.
This paper presents an effective medium approach to calculate the attenuation and phase constants of modes in a 3D connected wire medium both below and above the plasma frequency. Physical and nonphysical modes in the structure are identified for all the important lattice directions. According to this, the medium behaves as an isotropic material in the vicinity of the plasma frequency. These results were compared with the numerical simulation and it was observed that the wave spreads below the plasma frequency along all the important lattice directions with the same attenuation constant. This implies isotropic behavior of the 3D wire lattice below the plasma frequency, and thus this medium can be considered as an isotropic negative permittivity medium.
In this paper a simple model has been introduced to simulate the propagation of signal in a so called edged microstrip transmission line (EMTL). EMTL is a transmission line in which the signal strip is laid on the edge of the structure (Fig. 1). First a simple structure of EMTL is modeled with an ordinary MTL with improved per unit length inductances and capacitances, and an additional resistance to represent the radiation from the edges. This method is then applied to model a multilayer cross orthogonal EMTL structure as shown in Fig. 2. The model is finally validated using full wave analysis simulator, HFSS. The S-parameters of our model show good agreement with the results of the full wave analysis (HFSS) up to some GHz.
Standard spectral-domain method (SDM) is one of the popular approaches to analyze frequency selective surfaces (FSS). However, it is inherently incapable of handling normal incidence because of its dubious definition of excitation fields, reflection and transmission coefficients using z-component of vector potentials. Moreover, as far as the author knows, it has never been applied to analyze FSS with gangbuster arrays. In this paper, an improved SDM, the vector spectral-domain method, is presented. By proving the equivalence of the spectra of unit cell current and element current, the scattered field from FSS structures is formulated in terms of spectraldomain element current instead of spectral-domain unit cell current. Galerkin's method is applied to obtain the unknown induced surface current. Well-established definition of excitation fields, reflection and transmission coefficients is adopted. Extensive experimental validation has been conducted.
Concentric circular antenna array (CCAA) has interesting features over other array configurations.A uniform arrangement of elements is assumed where the interelement spacing is kept almost half of the wavelength and the array parameters such as the steering matrix and gain are determined.The array performance such as beam power pattern, sidelobe level and beamwidth are discussed in two cases of central element feeding.The two cases are compared showing the reduction in the sidelobe level to more than 20 dB in the case of central element feeding without extra signal processing especially for smallsized arrays that have smaller number of elements and rings.
In this paper, a tabusearc h tracker with adaptive neurofuzzy inference system (TST-ANFIS) is presented for multiple target tracking (MTT). First, the data association problem, formulated as an N-dimensional assignment problem, is solved using the tabu search algorithm (TSA), and then the inaccuracies in the estimation are corrected by the adaptive neuro-fuzzy inference system (ANFIS). The performances of the TST-ANFIS, the joint probabilistic data association filter (JPDAF), the tabusearc h tracker (TST), Lagrangian relaxation algorithm (LRA), and cheap joint probabilistic data association with adaptive neuro-fuzzy inference system state filter (CJPDA-ANFISSF) are compared with each other for six different tracking scenarios. It was shown that the tracks estimated by using proposed TST-ANFIS agree better with the true tracks than the tracks predicted by the JPDAF, the TST, the LRA, and the CJPDAANFISSF.
A novel structure for the capacitive micromachined switches with low actuation voltage is proposed. In this structure both contact plates of the switch are designed as displaceable membranes. Two structures with similar dimensions and conditions, differing on only the number of the displaceable beams are analytically investigated as well as simulated using ANSYS software. The obtained results indicate about 30% reduction in actuation voltage from the conventional single beam to our proposed double beam structure. The stress on the beam due to the actuation voltage is also reduced increasing the switching life time. The dynamic simulation results in switching time of 6.5 μsec compared to the 8.9 μsec of the analytical results. It can be implemented by the well established surface micromachining for RF applications.
The far-field radiation characteristics of an infinitesimal dipole embedded between two partially reflective surfaces (PRS) to obtain high directivity are studied analytically. The analysis is based on integral summation of spectral radiation fields of the source in cylindrical coordinate, so that we can find the effects of transmission and reflection coefficients of PRS on all components of primary radiation source. The analysis shows that due to the existence of TEz and TMz modes for horizontal dipole source, the effects of PRSs are different for each mode. Also, this study shows that by adjusting the spacing of the plates, it is possible to achieve high directive multibeam patterns.
In this paper a Polarized Optical Orthogonal Code (Polarized-OOC) is proposed by exploiting the polarization property of the fiber and the chip's polarization state. The polarized-OOC code is generated using the concept of Mark Position Difference (MPD) set. Polarized-OOC code cardinality is shown to be two times that of the conventional OOC which reflects an increase in the number of supported users. Furthermore, since the correlation properties of the constructed code are the same as that of conventional OOC, error rate performance is evaluated in the same way as in conventional OOC. Also, a simple procedure for fiber-induced polarization rotation compensation is introduced. We then use simulations to show that relative polarization axis misalignment between the desired user and interfering users leads to violation of the correlation properties of the proposed code.
The properties of a grounded dielectric slab with double negative (DNG) metamaterials are investigated in this paper. Dramatically different dispersion curves of evanescent surface modes (electromagnetic fields exponentially decay both in air and inside the slab) are observed. They are highly dependent on the medium parameters. As the counterpart of the improper complex leaky modes in a double positive (DPS) medium, the complex modes in a DNG medium are proved to be exclusively proper. They have exponentially decaying fields in the air region and are termed complex surface modes. It is found that there are an infinite number of complex surface modes and they cannot be suppressed. The Poynting vectors of complex surface modes are studied and it is proved that their integrals along the transverse direction are simply zero. The complete mode spectrum of the dielectric slab for both DPS and DNG media are tabled and compared. Surface wave suppression is discussed and its necessary and sufficient conditions are presented.
Based on a generalized Helmholtz's identity, definitions of an irrotational vector and a solenoidal vector are reviewed, and new definitions are presented. It is pointed out that the well-known uniqueness theorem of a vector function is incomplete. Although the divergence and curl are specified, for problems with finite boundary surfaces, normal components are not sufficient for uniquely determininga vector function. A complete uniqueness theorem and its two corollaries are then presented. It is proven that a vector function can be uniquely determined by specifyingits divergence and curl in the problem region, its value (both normal and tangential components) on the boundary.
In this paper, a conceptual schematic for calibration of large phased array antenna is presented. Derived from an earlier work by the authors, the presentation demonstrates a simple yet innovative schematic of inserting time delay units with each element in the array which can be used to generate both SUM and DIFFERENCE pattern. Both these patterns are electronically steerable. The calibration is done using SUM-DIFFERENCE pattern. PIN switches are used to insert proper time delay units. Thus the schematic is completely programmable using a microcontroller to control the insertion of time delay. The details of the schematic is presented along with the generated antenna patterns.
Geometry of grating structure has been analyzed to maximize electromagnetic energy deposition onto the active region of a silicon photodetector. The concept of Brewster angle to minimize reflection from the grating surface and a differences-in-time technique to focus incoming electromagnetic radiation on the substrate has been applied to optimize the grated structure that amplifies transmitted energy through grating-substrate interface. The computed electric field at the interface for the new grating geometry has been found to be approximately 1.5 times higher than that of a square-shape gratings reported earlier. Also the average power depositions and electric field distributions on the grating-substrate interfaces have been studied which revealed the superiority of the proposed optimum structure.
This paper presents a planar microstrip-fed tab monopole antenna for ultra wideband wireless communications applications. The impedance bandwidth of the antenna is improved by adding slit in one side of the monopole,in troducing a tapered transition between the monopole and the feed line,and adding two-step staircase notch in the ground plane. Numerical analysis for the antenna dimensional parameters using Ansoft HFSS is performed and presented. The proposed antenna has a small size of 16 x 19mm,and provides an ultra wide bandwidth from 2.8 to 28 GHz with low VSWR level and good radiation characteristics to satisfy the requirements of the current and future wireless communications systems.
In this phase of the attempt to advance finite dimensional algebraic function approximation technique in eigenvalue problems of lossless metallic guides filled with anisotropic and/or inhomogeneous media,to exact analysis in infinite dimensions,it is seen that the problem in infinite dimensions,can be reduced to finite dimensions,b y virtue of a result in perturbation theory. Furthermore,it is found that analysis results of algebraic function approximation,can be adapted to infinite dimensions too,at worst by introduction of some additional arguments.
Theoretical results on the effect of antenna mutual coupling (MC) on capacity of multiple-input multiple-output (MIMO) wireless channels are presented in this paper with particular emphasis on the case of high signal to noise ratio (SNR) scenario. Two cases are considered, 1- channel capacity variations due to MC effect on correlation properties and target average receive SNR and 2- channel capacity variations due to MC effect on correlation properties at fixed average receive SNR. It is shown that the effect of MC on MIMO channel capacity can be positive or negative depending on the propagation environment spatial correlation properties and the characteristics of the transmitter and receiver MC matrices. Conditions where MC has positive and negative effects on MIMO channel capacity in the two considered cases are identified. Numerical results for half wavelength dipole antenna supporting the theoretical observations are presented.
A general method is proposed to analyze periodic or aperiodic Coupled Nonuniform Transmission Lines (CNTLs). In this method, the per-unit-length matrices are expanded in the Fourier series. Then, the eigenvalues of periodic CNTLs and so the S parameters of aperiodic CNTLs are obtained. The validity of the method is studied using a comprehensive example.
The rigorous modeling and analysis of electromagnetic wave transformation and radiation from the periodic boundary of metamaterial are presented. The nature of the phenomenon of resonant radiation and the influence of various parameters on it are investigated. The study is carried out with the objective of potential applications to antenna design. Simulated results show that very high directivity can be obtained and that beam steering can be achieved by adjusting proper parameters.