A Cross-Correlation-Based Approach to Pattern Distortion and Mutual Coupling for Shared-Aperture Antennas

This paper proposes a pattern distortion coefficient as a new figure of merit to quantitatively evaluate both mutual coupling and pattern distortions in multi-antenna systems. The proposed coefficient is defined as a cross correlation between unaffected and affected far-field patterns of antennas under test, and the input patterns are weighted using a Gaussian function to consider the target operation angle. The feasibility of the proposed approach is validated using a two-antenna system composed of an inverted-F antenna and a microstrip patch antenna, and the amount of mutual coupling is adjusted by changing the distance between the two antennas. The evaluation is further extended to a single-antenna system with a conducting wall that produces strong platform effects with serious pattern distortions. The results demonstrate that the proposed figure of merit provides quantitative insight into the amplitude and phase distortions of far-field patterns that can be caused by both mutual coupling and platform effects.

NALYSIS OF FORMATION OF VISCOUS HEAT CONDUCTING GAS FLOWSFOR SMALL PERTURBATIONS OF PARAMETERS

Formation of one-dimensional flows arising as a result of interaction of a viscous heat-conducting gas and a heat-conducting wall in the process of reflection of a normally incident weak shock wave is considered. Formation of the flow field with small perturbations of parameters is studied on the basis of the Navier -Stokes equations linearized around the values of the parameters in the initial state, and the wall temperature distribution is modeled by linear heat equation. Analytical solutions of the linearized system of equations are obtained that allow one to analyze the influence of viscosity, thermal conductivity, and other factors on the formation of a continuous flow field structure with the formation of dissipative and ideal inviscid and non-heat-conducting zones.

The DRBEM solution of Cauchy MHD duct flow with a slipping and variably conducting wall using the well-posed iterations

The present study focuses on the numerical investigation of the Cauchy Magnetohyrodynamic (MHD) duct flow in the presence of an externally applied oblique magnetic field, with a slipping and variably conducting wall portion of the duct walls. The underspecified and overspecified boundary informations for the velocity of the fluid and the induced magnetic field on both slipping and variably conducting duct wall and its opposite part, respectively, constitutes the Cauchy MHD duct flow problem. This study aims to recompute the velocity of the fluid and induced magnetic field with specified slip length and conductivity constant, respectively, on the underspecified wall which is both slipping and variably conducting. The governing coupled convection-diffusion type MHD equations for the direct and inverse formulations are solved in one stroke using the dual reciprocity boundary element method (DRBEM). Both the velocity and induced magnetic field and their normal derivatives to be used as overspecified boundary conditions for the construction of Cauchy problem are obtained through the direct formulation of the problem. The well-posed iterations are used in the regularization of the ill-conditioned systems of linear algebraic equations resulting from the DRBEM discretization of Cauchy problem (inverse problem). Numerical solutions for the slip velocity and induced magnetic field are obtained for Hartmann number values $M$=5, 10, 50. The main advantages of the DRBEM are its boundary only nature and the capability of providing both the unknowns and their normal derivatives on the underspecified walls so that the conductivity constant and the slip length between them can be recovered at a low computational expense.

Influence of Axial Magnetic Field on Swirling Flow and Vortex Breakdown Zones in a Cylindrical Cavity with a Rotating Lid

In this study, behavior of swirling flow under the influence of axial magnetic field in a cylindrical container with a top rotating disk has been probed. The flow is assumed to be axisymmetric for the parameters considered. The domain consists of a cylindrical cavity packed with viscous and electrically conducting metallic liquid. The qualitative effect of magnetic field is manifested in terms of torque coefficient evaluated on the rotating lid as well as the fixed end wall. Effects of the magnetic field on the zones of vortex breakdown, in the Aspect ratio (AR), Reynolds number (Re) plane, for the top rotating lid with all sides electrically insulated have been developed. Moreover, it is found that one can control the behavior of flow with help of a proper choice of the electric conducting wall.