S. Cogollos

Efficient modal analysis of arbitrarily shaped waveguides composed of linear, circular, and elliptical arcs using the BI-RME method

This paper deals with the accurate and efficient modal analysis of arbitrarily shaped waveguides whose cross section is defined by a combination of straight, circular, and/or elliptical arcs. A novel technique for considering the presence of circular and/or elliptical segments within the frame of the well-known boundary integral-resonant mode expansion (BI-RME) method is proposed. This new extended BI-RME method will allow a more accurate solution of a wider number of hollow conducting waveguides with arbitrary profiles, which are usually present in most modern passive waveguide components. To show the advantages of this new extended technique, the modal chart of canonical (circular and elliptical) waveguides, as well as of irises with great practical interest (i.e., cross-shaped irises with rounded corners) has been first successfully solved. Next, a computer-aided-design software package based on such a novel modal analysis tool has first been validated with the accurate analysis of a referenced complex dual-mode filter, and then applied to the complete design of a novel twist component for K-band application based on circular and elliptical waveguides. A prototype of this novel device has been manufactured and measured for verification purposes.

A new hybrid mode-matching/numerical method for the analysis of arbitrarily shaped inductive obstacles and discontinuities in rectangular waveguides

A new and efficient hybrid mode-matching method is presented for the analysis of arbitrarily shaped inductive obstacles and/or discontinuities in a rectangular waveguide. The irregular region with obstacles and/or discontinuities is characterized using a full-wave hybrid spectral/numerical open-space technique expanding the fields in cylindrical wave functions. Next, a full-wave mode-matching procedure is used to match the cylindrical wave functions to guided modes in all ports and a generalized scattering matrix for the structure is finally obtained. The obstacles can be metallic or dielectric with complex permittivities and arbitrary geometries. The structure presents an arbitrary number of ports, each one with different orientation and dimensions. The accuracy of the method is validated comparing with results for several complex problems found in the literature. CPU times are also included to show the efficiency of the new method.

Design of Ultra-Wideband Substrate Integrated Waveguide (SIW) Filters in Zigzag Topology

In this letter we propose a modified substrate integrated waveguide (SIW) zigzag filter topology, which allows the flexible introduction of extra cross-couplings between non adjacent resonators. This novel topology permits to control the location of the transmission zeros, thus improving the resulting filter selectivity. Therefore, it has been used to design filters in compliance with the restrictive ultra-wideband European mask. In order to validate the new proposed topology, two filter prototypes have been designed, manufactured and measured, showing very good agreement with simulation data.

Evaluation of time domain electromagnetic fields radiated by constant velocity moving particles traveling along an arbitrarily shaped cross-section waveguide using frequency domain Green's functions

[1] A technique for the accurate computation of the time domain electromagnetic fields radiated by a charged distribution traveling along an arbitrarily shaped waveguide region is presented. Based on the transformation (by means of the standard Fourier analysis) of the time-varying current density of the analyzed problem to the frequency domain, the resulting equivalent current is further convolved with the dyadic electric and magnetic Green’s functions. Moreover, we show that only the evaluation of the transverse magnetic modes of the structure is required for the calculation of fields radiated by particles traveling in the axial direction. Finally, frequency domain electric and magnetic fields are transformed back to the time domain, just obtaining the total fields radiated by the charged distribution. Furthermore, we present a method for the computation of the wakefields of arbitrary cross-section uniform waveguides from the resulting field expressions. Several examples of charged particles moving in the axial direction of such waveguides are included.

Synthesis and Design Procedure for High Performance Waveguide Filters Based on Nonresonating Nodes

The synthesis and design of filters with nonresonating nodes (NRN) is applied to a practical case of hard requirements, with the aim of demonstrating the practical limits of such technique. An eight pole full inductive waveguide filter for space applications has been designed using a distributed model with frequency dependent inverters. Furthermore, the filter has been slightly tapered to scatter spikes due to the NRN unwanted resonances following a minimum dispersion criterion and maximum bandstop free of spurious. This feature has been incorporated into the distributed model showing down-to-earth designs from the very beginning of the design process.

A Systematic Design Procedure of Classical Dual-Mode Circular Waveguide Filters Using an Equivalent Distributed Model

In this paper, we propose a systematic procedure for the accurate design of classical dual-mode filters in circular waveguide technology. The design procedure is based on the previous synthesis of an intermediate distributed model, which links the standard lumped (or coupling matrix) elements circuit with the practical waveguide realization. We then show how the equivalent distributed model can be directly used to obtain the physical dimensions of these filter components (typically rectangular and cross-shaped irises, as well as tuning and coupling screws). The value of this paper lies in the fact that the proposed design strategy provides the final dimensions of these complex structures with unprecedented levels of accuracy and numerical efficiency, as it is shown through two dual-mode filter designs for narrowband applications, and measurements of a manufactured prototype.

A rigorous and efficient full-wave analysis of uniform bends in rectangular waveguide under arbitrary incidence

In this paper, a rigorous full-wave analysis of uniform bends in rectangular waveguides is performed. An accurate and efficient method-of-moments solution combined with the generalized-admittance-matrix (GAM) formulation is proposed in order to achieve a full-wave characterization of the analyzed structures. This full-wave modal solution turns out to be necessary for modeling complex microwave devices involving an arbitrary number of discontinuities between curved and straight waveguides, where all the modes of the involved guides are excited. The key feature of the presented method lies in the GAM representation of single and cascaded curved E- and H-plane uniform bends, which allows the construction of accurate models of the investigated discontinuities. To validate the theory, the convergence of the method is discussed and comparisons between our simulations and theoretical and experimental data are presented. The excellent behavior of our results, together with the computational efficiency of the proposed method, proves that the developed computer-aided-design tool can be successfully used in the design of complex microwave subsystems involving curved waveguides.

CAD of complex passive devices composed of arbitrarily shaped waveguides using Nystro/spl uml/m and BI-RME methods

In this paper, a novel computer-aided design (CAD) tool of complex passive microwave devices in waveguide technology is proposed. Such a tool is based on a very efficient integral-equation analysis technique that provides a full-wave characterization of discontinuities between arbitrarily shaped waveguides defined by linear, circular, and/or elliptical arcs. For solving the modal analysis of such arbitrary waveguides, a modified version of the well-known boundary integral-resonant-mode expansion (BI-RME) method using the Nystro/spl uml/m approach, instead of the traditional Galerkin version of the method of moments, is proposed, thus providing significant savings on computational costs and implementation complexity. The novel theoretical aspects of this Nystro/spl uml/m approach, as well as their impact on the original BI-RME formulation, are fully described. Comparative benchmarks between this new technique and the classical BI-RME formulation using Galerkin are successfully presented for the full-wave analysis of frequently used irises (i.e., rectangular cross-shaped and circular multiridged) and for the CAD of complex waveguide components (such as rectangular waveguide filters considering mechanization effects and dual-mode circular waveguide filters with elliptical irises).

Accurate consideration of metal losses in planar waveguide junctions using an efficient integral equation technique

Metal losses in passive waveguide devices are more pronounced and hazardous at higher frequencies. In this paper, we propose a very efficient integral equation technique for the accurate consideration of losses in the metal walls of any planar waveguide junction. For verification purposes, the results provided by the novel theory are successfully compared with those obtained with a lower efficiency commercial software. Combining this novel technique with a perturbation method that includes propagation losses, we have been able to predict all the losses effects in a 4-pole coupled cavities filter.

Automated design of waveguide filters using Aggressive Space Mapping with a segmentation strategy and hybrid optimization techniques

Microwave waveguide filters are key elements present in many communication systems. In recent times, increasing efforts are being devoted to the development of automated Computed Aided Design (CAD) tools of such devices. In this paper a novel CAD tool which improves the efficiency and robustness of the classical Aggressive Space Mapping (ASM) technique is presented. The use of a new segmentation strategy and the hybridization of various optimization algorithms is proposed. The CAD tool has been successfully validated with the design of a real H plane filter for an LMDS application.