In this work, an efficient analysis of radiating structures based on bodies of revolution is dealt with. The procedure is a hybrid method based on a segmentation of the structure into two-dimensional regions, finite elements and a spherical computation domain surrounding the antenna, defining a boundary or port where a spherical mode expansion of the fields is used. A reduced order model is computed for a fast frequency sweep. To validate this method, some structures based on bodies of revolution as a rod dielectric antenna, conical dielectric-loaded horns, profiled horns and a monopole-dielectric resonator antenna are studied and results are compared with those demonstrated by other authors. The design of a smooth-walled horn by means of the optimization of the profile is also carried out.

Abstract-This letter describes an efficient algorithm to predict the RF gas breakdown power threshold in microwave devices with complex geometries. The two necessary calculations when investigating such a phenomenon have been performed: on the one hand, the computation of the electromagnetic fields inside the structure and, on the other hand, the determination of the breakdown onset itself. The electromagnetic fields are solved by means of modal techniques and coupled to the free electron continuity equation, which is solved by the Finite Element Method. Proceeding in this way, a very simple criterion to find out whether microwave corona breakdown will take place is derived. This numerical implementation of the developed algorithms has been tested with other theoretical approaches and with experimental measurements, showing very good agreement.Index Terms-Electromagnetic simulation, gas discharge, high power, microwave breakdown threshold, microwave filters.

A global optimization method for the design of arbitrarily shaped H‐plane passive waveguide devices is presented. An adaptive simulated annealing algorithm (SA) is used to avoid local minima. No information on the initial shape is introduced. A hybrid method based on the segmentation technique, the finite‐element method, and a matrix Lanczos–Padé algorithm (SFELP) adapted to 2D space (2D SFELP) efficiently calculates the wideband response. Technological constraints and mechanical tolerances are taken into account in the design process. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 360–367, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20987

The DGFs appearing in these solutions are for a dielectric-magnetic medium with a distinguished axis, and are available as [4]:whereReversing the transformation given by Eqs. (13)- (15), we find the sought-after DGFs as follows:G m ͑r, s͒ ϭ r ␣ exp͓Ϫik 0 m ⅐ ͑r Ϫ s͔͒␣These expressions can be put in the same form as the DGFs provided in Chen's textbook [2, Chap. 11]. Axisymmetric devices have the advantage of symmetry, which simplifies the manufacture process. For this reason, they are extremely popular for applications at microwave and millimeterwave frequencies. High-performance horns, which feed large satellite-communication and radar antennas, and small feeds for terrestrial communications have been designed by using geometries based on bodies of revolution. Canonical forms as conical profiles do not always satisfy specifications, so corrugated horns, dielectric loaded and/or lens-corrected conical horns, dielectric cones, and cylinders, as well as compact profiled horns, have been studied in an attempt to correct a specific parameter of the antenna, or to try to reduce the size and weight of the structure. Horns are usually treated as apertures so as to find their radiation characteristics. The fields in the aperture are calculated as the propagation of modes of spherical Bessel function and Legendre polynomials [1]. The radiated field are obtained through the fieldequivalence principle [2]. This technique has not taken into account the external currents and is not applicable to arbitrary profiles. Nowadays numerical methods have been developed to correct these limitations. Because of the large size of these antennas, the method of moments (MoM) has been a common tool for their analysis and design. However, this approach is not efficient when inhomogeneous materials are present. The mode-matching method (MM) is a useful technique, but it has to be applied at many steps or sections throughout the structure. The finite-element method (FEM) has also been used in these applications. OPTIMIZATION OF ARBITRARILY SHAPED DIELECTRIC AXISYMMETRIC HORNS THROUGH FINITE ELEMENTS AND THE ANNEALING ALGORITHMIn this work, we have developed a CAD-oriented procedure based on the SFELP [3] method and an expansion by means of spherical modes on the outer boundary of the domain [4], but adapted to axisymmetric antennas in a similar way to those used in [5], although using curved higher-degree finite elements. The antenna is studied as a circuit characterized by the generalized scattering matrix (GSM) in which the radiating region is modeled by a spherical computational domain where a spherical modes expansion of the fields is used. The domain is enclosed by a spherical port.The SFELP method allows full-wave analyzing of arbitrary profiles taking into account all currents, even those far from the radiant aperture. We develop this tool in connection with a global optimizer that finds the absolute minimum across several iterations. This intensive use of the analyzer can be afforded because of the high efficiency of the SFELP.Finall...

An accurate and fast neural model for complex microwave circuits is efficiently obtained by using segmentation and exploiting the knowledge of frequency response obtained from reduced order models. Information arriving from the excited modes in the connection ports of the regions to be modeled is included analytically. The frequency response modeling is similar to that of reduced order Padé models, which are used to compute the necessary training data easily. Overall optimization can then be used efficiently. Several examples that illustrate the capacities of the method are also presented. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 655–659, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22448