Mobile broadband communication is experiencing rapid growth in the following sections: technology,range of services and marketing target groups. This growth has driven research and development activities towards advanced high-data-rate wireless systems, with improved network performance. A typical example of technology thrust in wireless communications is the use of adaptive antennas at the transceivers, in association with advanced array signal processing. Although the mass deployment of adaptive array systems has not achieved the desired levels yet,there are many examples of improved cell coverage, link quality and system capacity at several networks. The performance of a six-beam switched parasitic array, in terms of carrier-to-interference ratio (CIR) measurement at the uplink direction, is presented in this paper. The switched parasitic array is designed with the aid of the method of genetic algorithms and the simulation results are compared with respect to those obtained when an omni directional antenna is used instead. The calculated CIR improvement reveals the superiority of the adaptive system compared to the conventional one.
Analysis of U-slot loaded patch stacked with H-shaped parasitic elements is given in this paper. It is found that the antenna exhibits dual resonance and both the resonance frequency (upper and lower) depends directly on slot width and inversely on slot length. Both upper and lower resonance frequency increase with increasing the value of h_{2}. Typically the bandwidth at lower and upper resonance is found 3.66% and 10.25% respectively. The radiated power at higher frequency (beamwidth 64^{o}) is 0.73 dB as compared to lower resonance frequency (beamwidth 71^{o}). The theoretical results are compared with the simulated data obtained from IE3D.
The approximate analytical solution of the integral equation concerning the current in a thin straight vibrator with complex surface impedance has been obtained. The vibrator is located in unlimited space and is excited in an arbitrary point along its length. The calculations have been made and the plots of electrodynamic characteristics of the vibrator, depending of the value and the type of its surface impedance and the excitation point location, are represented. The comparative analysis between the calculated and the experimental data and also the results, obtained by the method of moments, are represented for perfectly conducting vibrators.
Diffraction of an electromagnetic plane wave from a slit in an impedance plane has been presented. The method is based on Maliuzhinets technique for impedance surfaces. Comparison of the field patterns with different values of the face impedance are also presented.
The matched filter (MF) is known as the fastest method for acquisition of DS-CDMA signals. Power consumption of the MF is a key issue for realizing multimedia hand-held terminals. We proposed a new Analog Matched Filter using Sample-and-Hold (S/H) circuit, which performs correlation between an input signal and a filtering coefficient employed for modulation in fully analog domain, eliminating the need to Analog-to-digital (A/D) conversion, so reduces power consumption and chip area. Simulation results reveal that the proposed circuit dissipates 2.3 mW power consumption at a chip rate of 16.7 MHz with 3.3 V power supply for 15 taps configuration. The proposed analog architecture could improve the performance of mobile terminals.
A new canonical scattering problem consisting of the propagation of the dominant TEM mode at the finite-length impedance discontinuity in the outer conductor of a coaxial waveguide is solved. The contributions from the successive impedance discontinuities are accounted for through the solution of a modified Wiener-Hopf equation. Some graphical results displaying the reflection and transmission characteristic are presented.
The performance of wideband radar system may be degraded by signal distortion occurring in anyplace of the transmission channel of the system. If the amplitude response is not flat or the signal delay is not constant in the transmission of the wideband signal, then signal distortion will occur, which can reduce the SNR and resolution. The available theory indicates that a small sinusoidal ripple variation in either amplitude-frequency or phase-frequency response of a linear system will cause signal distortion and the phenomena of paired echoes in the output signals of the time domain. In this paper, whether a dispersive transmission line with discontinuities will lead to the phenomena of paired echoes is discussed by means of finite difference time domain (FDTD) method and theoretical analysis. The results show that the technique of paired echoes is unsuited to analyze the influence of dispersive transmission line with discontinuities on time domain pulse signal. The method of Taylor series expansion shall be chosen as a more appropriate method. Meanwhile, simulations also show that a pulse signal transmitting in dispersive transmission lines with discontinuities including passive components such as filters and directional couplers will not lead to the phenomena of paired echoes.
Rain rate and rain attenuation predictions are one of the vital steps to be considered when analyzing a microwave satellite communication links at the Ku and Ka bands. In this paper, tools for the prediction of rain rate and rain attenuation are presented in the form of contour maps for Nigeria using a massive rainfall data bank of 30 years which are taken from measurements made from the coast to the arid region of Nigeria. Rain-rate maps for the country of Nigeria were developed using the models purposely designed for tropical zones while ITU-R models were used for the rain-attenuation maps. The information from these maps will be a good preliminary design tools for both terrestrial and earth-satellite microwave links and also provide a broad idea of rain attenuation for microwave engineers.
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, the 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 and pros 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.
Perfect electromagnetic conductor (PEMC) has been introduced as a generalization of both the perfect electric conductor (PEC) and the perfect magnetic conductor (PMC). In the present paper, the basic problem of reflection and transmission of an obliquely incident plane wave at the interface of a PEMC half space or slab is considered. It is found that the field outside the PEMC medium can be uniquely determined but the interior field requires some assumptions to be unique. In particular, definition of the PEMC-medium condition as a limit of a Tellegen-medium condition and extraction of certain virtual fields (metafields) are shown to make the field inside the PEMC medium unique.
Retrodirective arrays have garnered much attention due to the unique feature of automatically responding to an interrogator without any prior knowledge of the location of the incoming signal. This paper describes the basic concept of retrodirective array technology, discusses the three retrodirective array topologies with their advantages and disadvantages. Characterizations of the selfsteering performance in a retrodirective antenna array are described. A series of array design considerations in the retrodirective array systems is presented, and further researches in this area are presented.
In this paper a transfer matrix treatment for the reflectivity and transmissivity spectra of electromagnetic waves propagating in a nano sized multilayer periodic structure has been presented. Effect of varying the angle of incidence on the photonic bandgaps is shown. The design of a tunable polarizer by reflection which is more efficient in comparison to that obtained by reflection from a single dielectric slab, has been suggested.
In this paper, a high data rate Ultra-Wideband Differential Transmitted-Reference (UWB-DTR) system which is one of the best and simplest available TR scheme is analyzed over IEEE 802.15.3a Channel Model 1 (CM1). We show that these systems need equalization in high data rate mode of operation because in such a case harsh nonlinear inter symbol interference (ISI) exists and degrades performance severely. The performance of the DTR system in CM1 is derived both analytically and via simulations by taking into account noise, inter path/pulse interference (IPI), and ISI. Uniform approximation for ISI distribution is proposed for the first time which gives a closer approximation than Gaussian one. All simulation and analytical results are obtained for CM1 but generalization to other channel models is also possible.
A full-wave analysis of the scattering parameters of a straight-to-bent microstrip line coupling is performed using a FEM technique. The numerical results, showing the influence played by the geometrical parameters of the structure on the electromagnetic coupling, are then employed to derive an equivalent circuit useful to be employed in CAD tools. A third order polynomial approximant useful to compute the equivalent circuit elements is finally provided.
The Sub-Entire-Domain (SED) basis function method has been applied to solve electromagnetic problems of irrectangular periodic structures with finite sizes efficiently. Three typical irrectangular periodic structures such as parallelogrammic periodic structures, triangular periodic structures, and trapeziform periodic structures are investigated using the SED basis function method. Just as the SED basis functions for rectangular periodic structures, the new SED basis functions for irrectangular periodic structures are defined on the support of each single cell, and the corresponding dummy cells are introduced to obtain the new SED basis functions. Using the proposed SED basis function method, the original large-scale problem is decomposed into two small-size problems. One is the determination of new SED basis functions, and the other is to solve the whole problem using MoM and SED basis functions. Numerical examples are given to prove the validity and efficiency of the new method.
For a long time power pattern synthesis has been considered to produce shaped beam patterns due to the number of degrees of freedom when compared with field pattern synthesis. However, severaladv antages exist if synthesis techniques are based on field patterns, since the relationship between the array factor and the source distribution is a Fourier transform. In this case, quicker and efficient algorithms are obtained with the Fast Fourier Transform (FFT) to perform the calculations. Therefore, this work presents a new technique that synthesizes shaped beam patterns through the control of non-uniformly samples of the array factor, both in amplitude and phase. The sample phases increase the number of degrees of freedom. To produce complex patterns, the sample phases of the shaped beam region are used to create more oscillations in the ripple structure than the ones produced with the realpatterns. Not only this procedure yields a narrower transition region between the beam zone and the sidelobe zone but also smaller dynamic range ratios are obtained. Furthermore, it is described how to impose nulls in prescribed directions of the complex patterns. Some examples are presented to demonstrate the application of the synthesis technique.
We present a generally symmetrical circuit model to describe all kinds of metamaterials with effective permittivity and permeability. The model is composed of periodic structures whose unit cell is a general T-type circuit. Using the effective medium theory, we derive analytical formulations for the effective permittivity and effective permeability of the circuit model, which are quite different from the published formulas [1, 2]. Rigorous study shows that such a generally symmetrical model can represent right-handed materials, left-handed materials, pure electric plasmas, pure magnetic plasmas, electric-type and magnetic-type crystal bandgap materials at different frequency regimes, with corresponding effective medium parameters. Circuit simulations of real periodic structures and theoretical results of effective medium models in this paper and in [1] and [2] are presented. The comparison of such results shows that the proposed medium model is much more accurate than the published medium model [1, 2] in the whole frequency band.
In this work, Support Vector Machine (SVM) formulation is worked out based upon ''L'' measured data for the resonant frequency, operation bandwidth, input impedance of a rectangular microstrip antenna. Results of the formulation are compared with the theoretical results obtained in literature, much better characterization is observed with greater accuracy. At the same time, Artificial Neural Network (ANN) is employed in generalization of the data on the resonant frequency, operation bandwidth, and input impedance of the antenna. Performances of the two advanced nonlinear learning machines are compared and superiority of the SVM is verified.
Magic tee is a widely used component in microwave systems; the four arms of a conventional magic tee direct at four different directions, which occupy much space and give inconveniences to the assemblage of a system. In this paper, a waveguide narrow-wall slot directional coupler and an E-plane dielectric loaded waveguide phase shifter are used to make up of a magic tee with four arms in the same H-plane. The narrow-wall slot directional coupler is analyzed with mode matching method and optimized with simulated annealing method, and the dielectric loaded waveguide phase shifter is designed with edge based finite element method. Numerical results of the magic tee are presented, which show that the performance of the designed magic tee is good.
The canonical problem of an extra-ordinary Transverse Electromagnetic wave propagating in a parallel plane waveguide with a semi-infinite upper conductor and loaded with magnetized plasma is considered. The homogeneous biasing constant magnetic field is assumed parallel to the substrate and normal to the wave propagation, which incidents normally on the truncated edge. The Wiener-Hopf technique is employed and the corresponding equations are formulated for the open-radiating structure as well as for a closed one resulting from the placement of a metallic shield parallel to the waveguide planes. Closed form field expressions are obtained for the shielded geometry, while the open geometry Kernel factorization is left for future extensions. Important non-reciprocal wave propagation phenomena are involved, which lend non-even function properties to the involved Kernels. Hence, their factorization becomes non-trivial requiring new mathematical approaches. Finally, a review of the involved non-reciprocal and/or unidirectional surface waves is given, which is related to the involved mathematical complexities.