Improved design procedure for double-ridged waveguides

This article presents a novel methodology for designing double-ridged waveguides by numerically optimizing their geometric shape such that they sustain the two prescribed lowest order modes. The field solution to the problem is obtained by using the finite element method. The performance of the microgenetic algorithm and the quasi-Newton methods is studied for carrying out geometry optimization. This generalized formulation is capable of handling inhomogeneous material fillings in the guide, and computational results are presented to demonstrate the versatility of the proposed technique. (C) 2002 Wiley Periodicals, Inc

An efficient solution of the generalized eigenvalue problems for planar transmission lines

This paper presents an efficient solution for solving the generalized eigenvalue equation arising in the finite-element (FE) formulation of propagation characterization of planar transmission-line structures. A two-dimensional (2-D) finite-element method (FEM) is used for analyzing the uniform planar transmission lines. The Arnoldi algorithm is used in conjunction with the multifrontal decomposition of the system matrix for solving the eigensystem. Convergence is typically obtained within a few iterations of the Arnoldi process, and the formulation has proven to be robust, even when dealing with a significantly large number of unknowns. Numerical results are presented for the case of a uniform microstrip line, which clearly show the computational savings resulting from the use of the present approach. (C) 2001 John Wiley & Sons, Inc

Full-wave analysis of microstrip lines on a highly lossy substrate

The finite-element method has been used for analyzing open microstrip line structures on highly lossy substrates. The geometry descritization has been carried out by using quadrilateral elements, and the spurious solutions art avoided by employing tangential vector formulation. The difficulties associated with finding the propagation constant of a highly lossy structure 13.1, solving a generalized eigenvalue problem are discussed. A methodology is presented,for a fast and efficient computation of the attenuation and propagation constants of the lossy transmission lines. Numerical results are presented to illustrate the application of the proposed approach for the case of an open microstrip line. (C) 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 325-329, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10908

Sidewall inclined slot in a rectangular waveguide: Theory and experiment

A novel analysis to compute the admittance characteristics of the slots cut in the narrow wall of a rectangular waveguide, which includes the corner diffraction effects and the finite waveguide wall thickness, is presented. A coupled magnetic field integral equation is formulated at the slot aperture which is solved by the Galerkin approach of the method of moments using entire domain sinusoidal basis functions. The externally scattered fields are computed using the finite difference method (FDM) coupled with the measured equation of invariance (MEI). The guide wall thickness forms a closed cavity and the fields inside it are evaluated using the standard FDM. The fields scattered inside the waveguide are formulated in the spectral domain for faster convergence compared to the traditional spatial domain expansions. The computed results have been compared with the experimental results and also with the measured data published in previous literature. Good agreement between the theoretical and experimental results is obtained to demonstrate the validity of the present analysis

Nonresonant edge slot antenna for phased array applications: Theory and experiment

The design and development of nonresonant edge slot antenna for phased array applications has been presented. The radiating element is a slot cut on the narrow wall of rectangular waveguide (edge slot). The admittance characteristics of the edge slot have been rigorously studied using a novel hybrid method. Nonresonant arrays have been fabricated using the present slot characterization data and the earlier published data. The experimentally measured electrical characteristics of the antenna are presented which clearly brings out the accuracy of the present method

A selective survey of the waveguide-fed slot radiators

Waveguide-fed slot radiators are widely used in several strategic applications. The published literature in this area is vast, spanning a period of nearly 50 years. There is a need for consolidating the information and present it at a glance, to aid future research. The purpose of this article is to present a survey of the published literature in the area of waveguide-fed slot radiators. Specifically, the topics covered include longitudinal/transverse roadwall radiating slots, dielectric filled/covered slots, compound/centred-inclined radiating slots, narrow wall slots, ridged waveguide slots, etc. This survey does not include the literature on the array design, as it would have resulted in limiting the information on the slot radiators. Besides, it is felt that the slot array analysis and design techniques would merit a survey of their own

Method-of-moments analysis of the narrow-wall slot array in a rectangular waveguide

The method-or-moments has been used for the analysis of the nonresonant narrow-wall slot array in a rectangular wave guide. As this approach works with the fundamental integral equations that describe the entire array, no assumptions about the aperture electric fields are required. Also, the equivalent circuit representation for the individual radiating slots used in earlier designs is not required in the present method, as it deals directly with slot aperture voltages. The effects of internal higher-order and external mutual couplings, and finite wall thickness are rigorously incorporated in the design. Expressions are presented for the input reflection coefficient, transmission coefficient, and the Car-field radiation pattern of the array. Numerical results are compared with the experimental results of a 78 element narrow-wall slot array. Good agreement has been observed between theory and experiment

Electro slag crucible melting for recycling of low oxygen high conductivity copper scrap

Recycling of oxygen free high conductivity (OFHC) copper scrap was carried out through a modified electro slag melting technique using a graphite electrode and graphite crucible. Of the three slags used, a cryolite based slag was found to yield copper ingots with low (2 to 40 ppm) oxygen content and high (up to 98% IACS) conductivity. A slag as well as graphite of high purity are essential since the impurities present in the slag and graphite may contaminate the copper during melting. Possible mechanisms of impurity (Fe, Si, Mg, Ca and S) pick-up by copper are discussed. Identical results were obtained using cathode copper instead of OFHC copper scrap indicating that the process may be used to produce low oxygen high conductivity copper ingots directly from cathode copper

Recycling of valuable scrap through electroslag processing

Recycling of metals and alloys is important for conservation of natural mineral resources, reduction in energy consumption and minimization of environmental pollution. Light scrap of reactive metals and alloys containing reactive elements is diffifult to recyle by conventional methods of melting. At the Defence Metallurgical Research Laboratory (DMRL), Hyderabad, electroslag melting technologies have been developed for recycling light scrap of valuable metals and alloys such as superalloys and oxygen free high conductivity (OFHC) copper. Conventionally, electroslag melting processes use consumable electrodes. Because of the difficulty in compaction of scrap into a consumable electrode of satisfactory quality, non-consumable electrodes such as graphite and water-cooled copper have been designed. Electroslag remelting using water-cooled non-consumable electrode was used to melt scrap of a nickel base superalloy. Sound ingots with smooth surface finish and properties comparable to vacuum melted superalloys could be obtained from scrap using this process. OFHC copper scrap was melted by a modified electroslag crucible melting process using graphite crucible and graphite electrode. Process parameters including slag composition were optimised to produce copper ingots with oxygen less than 10 ppm and electrical conductivity approximate to 100% IACS. The same process was also utilised to produce copper-chromium (Cu-Cr) ingots starting from copper scrap and pure chromium metal. The alloy exhibited superior room temperature tensile properties and high temperature ductility. Alternatively, Cu-Cr could also be produced by in-situ reduction of chromium oxide by aluminium during electroslag crucible melting