In this paper, we investigate the thermal noise behavior of the multi-antenna communication systems, when antenna elements are closely spaced. We analyze the mutual coupling effect on thermal noise. We apply the Nyquist's thermal noise theorem to determine thermal noise power in the multi-antenna system and to confirm the partial correlation of thermal noise for antenna spacing lower then one wavelength. Simulation results confirm the decrease of thermal noise power level when antenna spacings drop below a half wavelength.
This paper proposes a new analysis of the transmission coefficient at normal incidence for 2-D periodic crystals (also called Electromagnetic Band Gap (EBG) structures), which are finite in the direction of wave-propagation and are composed of metallic wires. The crystal is considered as a set of parallel Partially Reflecting Surfaces (PRSs), whose transmission and reflection characteristics are obtained rigorously using the Finite Difference Time Domain (FDTD) method. The transmission coefficient of the EBG structure is then obtained by using a plane-wave cascading approach considering single mode interactions between PRSs. The accuracy of the results given by the hybrid method is assessed compared to those obtained directly by the Finite Difference Time Domain (FDTD) method. The minima and maxima envelops and the resonance frequencies of the transmission coefficient are studied, with analytical expressions, for both, excitation from outside and excitation from inside. A discussion is also presented concerning the strength of the coefficient greater than one obtained when the plane-wave source is inside the EBG structure. In addition, by using a transmission line model, a normalized version for this coefficient is proposed, which considers the available power by the source.
A new time-domain theory for waveguides has been presented in the paper. The electromagnetic fields are first expanded by using the complete sets of vector modal functions derived from the transverse electric field. The expansion coefficients are then determined by solving inhomogeneous Klein-Gordon equation in terms of retarded Green's function. The theory has been validated by considering propagation problems excited by various excitation waveforms, which indicates that the higher order modes play a significant role in the field distributions excited by a wideband signal.
The performance of mobile cellular radio networks is limited by the level of cochannel interference that can be tolerated. The use of antennas arrays is very helpful in enhancing the performance and capacity of the wireless communication system. This paper presents a method for antenna pattern synthesis that suppress multiple interfering narrow or wide band signals while receiving the desired signal by controlling only the phase. Excitation phases are computed using the Sequential Quadratic Programming (SQP) technique. This method transforms the nonlinear minimization (or maximization) problem to a sequence of quadratic subproblems, based on a quadratic approximation of the Lagrangian function.
In this article, a theoretical and computational analysis has been made to obtain the modal dispersion characteristics of an unconventional optical waveguide with a Piet Hein core cross section having a conducting sheath helix winding on its core-cladding boundary. A simple analytical method using the vector boundary conditions has been utilized to get the modal eigen value equation. From this equation dispersion curves are obtained and plotted for some particular values of the pitch angles of the winding. Next, these predicted results are compared with those of a new optical fiber having a conducting sheath helix winding on its core-cladding boundary. It is seen that the cutoff values are somewhat lower for the Piet Hein lightguide than those for the circular guide. This is not unexpected since the Piet Hein curve approaches the shape of a square. The introduction of a conducting helical winding leads to a modification of the modal characteristics of the lightguides and gives us an additional means to control them.
Creeping waves propagate in the shadow along the surface of a convex body. In the case of a perfectly conducting body coated with high index anisotropic dielectric, this surface can be described by anisotropic impedance boundary condition. In a previous paper the general case of anisotropic impedance was studied. In this paper we discuss a special case characterized by a degenerated impedance matrix. The ansatz for ordinary creeping waves does not allow the asymptotics to be constructed and a new ansatz is suggested. In contrast to the usual one, this ansatz contains an additional quick factor proportional to k1/6 (where k is the wavenumber). As a result, the field is described by an asymptotic sequence in inverse powers of k1/6 . We derive the principal order term of the asymptotics and discuss specific properties of creeping waves on a surface with degenerated impedance.
Fractional curl operator has been utilized to wave propagation in lossless, isotropic, homogeneous and reciprocal chiral medium when it contains interfaces. The fractional solutions for the corresponding standing wave solution and transverse impedance are determined. Equivalent fractional non-symmetric transmission line has also been analyzed.
A general method is introduced to frequency domain analysis of lossy Inhomogeneous Planar Layers (IPLs). In this method, the IPLs are subdivided to several thin homogeneous layers, at first. Then the electric and magnetic fields are obtained using second order finite difference method. The accuracy of the method is studied using analysis of some special types of IPLs.
Permittivity and conductivity studies of corn syrup in various concentrations are performed using coaxial cavity perturbation technique over a frequency range of 250 MHz-3000 MHz. The results are utilized to estimate relaxation time and dipole moments of the samples. The stability of the material over the variations of time is studied. The measured specific absorption rate of the material complies with the microwave power absorption rate of biological tissues. This suggests the feasibility of using corn syrup as a suitable, cost effective coupling medium for microwave breast imaging. The material can also be used as an efficient breast phantom in microwave breast imaging studies.
In this work, we present a semi empirical approach and the analytical model on how to predict the total path loss in various indoor communication links, taking into account the new analytical methods of the derivation of the fading phenomenon between floors and along corridors, respectively. We take into account the stochastic method of slow and fast fading estimations, caused by diffraction and multipath phenomena, respectively. The statistical parameters required for statistical description of the diffraction and multipath phenomena, such as the standard deviations of the signal strength due to slow and fast fading are obtained from the corresponding measurements. The path loss characteristics together with evaluated parameters of slow and fast fading give a more precise link budget predictor, and obtain full radio coverage of all subscribers located in the area of service inside each building. Based on strict and completed path loss prediction, an algorithm of link budget performance is presented for different scenarios of radio propagation within indoor communication links. Results of proposed unified approach are compared with the analytical Bertoni's model, which is well-known and usually used in link budget design in various indoor environments. The results are also compared with measurements carried out for different propagation scenarios, along corridor and between floors, occurred in the indoor communication channels. A better agreement with experimental data is obtained compared to the model in consideration.
The goal of the present paper is two folded. The first, the methodological one, is the complementation of well established in diffraction theory of gratings C method with certain elements of spectral theory and the development of interactive numerical algorithm that made feed back conjunction between diffraction and spectral problems. As a natural result the second goal appeared: the appearing of such tool for numerical experiments resulted in profound qualitative and quantitative study of rather peculiar phenomena in resonant scattering from periodic surface. Special attention has been paid to the investigation of electromagnetic waves diffraction from periodic boundaries of material with single and double negative parameters.
We present an efficient modal method to calculate the two-dimensional Green's function for electromagnetics in curvilinear coordinates. For this purpose the coordinate transformation based differential method, introduced for the numerical analysis of surface-relief gratings, is directly used with perfectly matched layers (PMLs). The covariant formalism Maxwell's equations, very convenient for the non-orthogonal coordinates formulation, also gives an unified analysis of PMLs. Numerical results for a line source placed above a perfectly conducting corrugated surface are presented.
To model periodic structures with oblique incident waves/scan angles in FDTD, the field transformation method is successfully used to analyze their characteristics. In the field transformation method, Maxwell's equations are Floquet-transformed so that only a single period of infinite periodic structure can be modeled in FDTD by using periodic boundary conditions (PBCs). A new discretization method based on the exponential time differencing (ETD) algorithm is proposed here for the discretization of the modified Maxwell's equations in the periodic FDTD method. This new discretization method provides an alternative way to discretize the modified Maxwell's equations with simpler updating forms that requires less CPU time and memory than the traditional stability factor method (SFM). These two methods have the same numerical accuracy and stability in the periodic FDTD method. Some validation cases are provided showing perfect match between the results of both methods.
Optical properties of generalized dielectric Fibonacci multilayer generated by the rule Sl+1 = Sn l Sm l-1 with a pair of positive integers m and n were studied. The initial generations S1 and S2 are taken as S1 = H and S2 = L where H and L are two elementary layers with refractive indices nL = 1.45 and nH = 2.3, respectively. In the following numerical investigation, we chose SiO2 (L) and TiO2 (H) as two elementary layers. We use the so-called "antitrace" map to determine the transmission spectra of the structures. Based on the representation of the transmittance spectra in the visible range an analysis depending on the pair (n,m) is presented. We show that the whole structure Sn l Sm l-1 has an interesting application for well selection pairs (m, n) values.
In the present paper, a combined method of auxiliary sources (MAS)-reaction matching (RM) approach is presented for the analysis of arrays of arbitrarily located cylindrical dipoles. It is shown that the addition of auxiliary monopole terminal sources to each array element results in a superior solution with regard to the numerical stability of the computed quantities, the behavior of the current distributions of the array elements and the resulting errors of the electric field boundary condition. Numerical results are presented for various representative array configurations, in order to illustrate the features of the proposed method and exhibit its advantages over conventional Method of Moments (MoM) schemes, especially in cases of moderately large-scale arrays. Finally, a few concluding remarks are discussed.
In the present paper a simple model has been given to simulate the signal propagation through cross orthogonal coupled strip lines in multilayer PCB board. First the structure has been analyzed using a full wave software (such as microwave office) then a simple and suitable lumped equivalent circuit is proposed for the coupled cross talk region. The values of the lumped equivalent circuit are then obtained using a simple method. These values are then optimized to fit the S-parameters obtained using full wave analysis. Finally the s-parameters of this equivalent circuit compared with the results of full wave simulations. The results show good agreement up to some GHz.
This paper presents an experimental Phased Array Antenna System operating at 10 GHz. Geometry of the antenna array is cylindrical. Antenna element excitation phases are adjusted at the intermediate frequency stage. Antenna element excitation amplitudes are taken to be constant. A least squares technique is used for phase computation and radiation pattern synthesis. The obtained radiation patterns provide steerable main lobes and nulls at predefined directions including control of the side lobes at specified levels. Units of the system are presented in detail and their architecture is explained. A phase calibration is used to compensate the system. Measurements of radiation patterns are presented and are compared with calculated patterns.
In this paper, the regular microstrip-fed dipole antenna with simplified balun is modified to improve the usable bandwidth by increasing the stability of the radiation patterns. The presented antenna consists of two parallel dipoles of different lengths to obtain two main resonances. The distance between the two dipoles is adjusted to reduce the return loss between the two main resonances. A wide usable bandwidth of more than 84% is obtained with high radiation pattern stability. The proposed antenna is simple and small in size. The results of a modified two-element array configuration from this antenna show that it is very good candidate for wideband phased array applications.
Submit
