J. Brandt

Fast CAD and optimization of waveguide components and aperture antennas by hybrid MM/FE/MoM/FD methods-state-of-the-art and recent advances

This paper presents an overview of the state-of-the-art of hybrid mode-matching (MM)/finite-element (FE)/method-of-moments (MoM)/finite-difference (FD) techniques applied for the rigorous, fast computer-aided design and optimization of waveguide components, combline filters, and coupled horns, as well as of slot arrays, and describes some recent advances. Related aspects involve the inclusion of coaxial and dielectric structures for related filters, the extension to multiports at cross-coupled filters, the rigorous consideration of outer and Inner mutual coupling effects at coupled horn and slot arrays, the application of the multilevel fast multipole algorithm for the more efficient MoM calculation part of horns and horn clusters, and the utilization of the MoM for the design of arbitrarily shaped three-dimensional waveguide elements. The described hybrid techniques combine advantageously the efficiency of the MM method with the flexibility of FE, MoM, and FD methods. Topical application examples demonstrate the versatility of the hybrid techniques; their accuracy is verified by available measurements.

Efficient hybrid MM/MoM technique for the CAD of circular combline filters with resonators of more general shape

A hybrid mode-matching (MM) / method-of-moment (MoM) technique is presented for the efficient CAD and optimization of circular combline filters involving more general elements like corrugated circular post and re-entrant resonators. Using the free-space Greens function, the proposed technique combines the high flexibility of the MoM with the efficiency of the MM method. A locally refined adaptive triangular surface mesh and the application of Rao-Wilton-Glisson (RWG) basis functions achieve the reliable modeling of arbitrarily shaped structures. The building blocks are combined by the generalized scattering matrix (GSM) allowing typical MM elements like irises to be efficiently included. The attractive feature of the proposed method is its short computation time (order of a few seconds per frequency point) achieving the full-wave optimization of such filters within reasonable times. The high versatility of the hybrid method is demonstrated at examples of practical interest; its efficiency and accuracy is verified by available measurements.

Direct EM based optimization of advanced waffle-iron and rectangular combline filters

A fast hybrid mode-matching (MM)/finite-element (FE) method is applied for the direct EM based optimization of advanced waffle-iron filters and coax-fed rectangular combline filters. The proposed technique, which combines the efficiency of the MM with the flexibility of the FE technique, achieves the direct EM based optimization of these components within typically an overnight run on a PC. The CAD method is verified by measurements.

Flexible hybrid MM/MoM technique for the CAD and optimization of arbitrarily shaped 3D waveguide components

A hybrid mode-matching (MM) / method-of-moment (MoM) technique is applied for modeling arbitrarily shaped 3D waveguide structures. Using the free-space Greens function, the attractive feature of this technique is the high flexibility of the MoM combined with the efficiency of the MM method. Its versatility is demonstrated at examples of practical interest, a compensated magic-tee and a combline filter with round posts. The efficiency and accuracy of the method is verified by reference calculations and measurements.

MM/FE/FD CAD Method for the Optimization of Waveguide Filters Including Structures of Arbitrary Shape and Coax Feeds

A fast full-wave CAD method is described for the accurate design and optimization of advanced waveguide components including cross-sections, planar structures, or 3D elements of arbitrary shape as well as coax feeds. The method is based on the combination of the mode-matching (MM) technique with the 2D finite-element (FE) and the 3D finite difference (FD) algorithm, which unites advantageously the flexibility of the FE and the FD methods with the efficiency of the MM technique. Typical design examples such as H-plane iris filters cut in the E-plane with finite radii and filters fed by coaxial waveguides demonstrate the usefulness of the presented CAD tool. The theory is verified by measurements.

Conical circular waveguide with side-coupled rectangular ports analyzed by a hybrid mode-matching/method-of-moment technique

A hybrid mode-matching (MM)/method-of-moment (MoM) technique is presented for the rigorous analysis of the six-port junction of a conical circular waveguide with four side-coupled rectangular waveguides. The effects of the cone and of aperture curvature are rigorously taken into account. The advantage of the conical structure in comparison with its cylindrical counterpart includes achieving additional design potential, which can be applied e.g. for ortho-mode transducers (OMTs) of improved performance. The accuracy and efficiency of the method are verified by comparison with reference values.

MM/FE CAD and Optimization of Rectangular Combline Filters

A rigorous and fast hybrid mode-matching (MM)/finite-element (FE) technique is presented for the CAD and optimization of coax-fed rectangular combline filters. The novelty of the formulation consists in the very efficient EM based modeling of these filter types including immediately three common coax feed forms (direct post, disc or probe coupling). The attractive feature of the hybrid approach is the combination of the computational speed of the MM technique with the flexibility of the FE method. This achieves the direct optimization of combline filters within typically an overnight run on a PC. Design examples for a variety of combline filters demonstrate the flexibility of the CAD method, experimental results show its validity for practical applications.

Higher Order Vector Bases for the Method of Moments Analysis of a Class of Waveguide and Dielectric Resonator Filters Involving Curved Boundaries

A combined electric field integral (EFIE) Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) surface integral equation technique is presented, in which divergence-conforming higher order vector basis functions are applied. Curved surfaces are modeled using curvilinear triangles in order to minimize geometrical modeling inaccuracies. Conforming vector bases provide appropriate continuity at material interfaces and allow for imposing boundary conditions on unknown fields or currents. The advantage of the proposed method against existing approaches is its higher efficiency and flexibility. The versatility and accuracy of the method are verified at typical filter examples by comparison with reference results.

Combined Surface Integral Equation Technique with RWG Basis Functions for the Analysis of a Class of Coax-Fed Dielectric Resonator Filters

A combined electric field integral (EFIE) Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) surface integral equation technique is presented, in which exclusively Rao-Wilton-Glisson (RWG) functions are used for basis functions. This yields the accurate analysis of coax-fed dielectric resonator filters. The advantage of the proposed method against existing approaches is its higher efficiency and flexibility. The versatility and accuracy of the method are verified by comparison with measured results

Multiport MM/FE technique for the efficient CAD of folded and cross-coupled rectangular combline filters

The hybrid mode-matching/finite-element (MM/FE) technique extended to multiports yields generalized scattering matrix (GSM) building blocks for the CAD of advanced coax-fed rectangular combline filters of improved performance. The novelty of the formulation consists in the very efficient EM based modeling of folded and cross-coupled rectangular combline filters that allows their optimization within typically an overnight run on a PC. Usual coax feeds (direct post, disc, probe or loop coupling) are directly included. The attractive feature of the hybrid MM/FE approach is the combination of the computational speed of the MM technique with the flexibility of the FE method also for this class of components. Design examples demonstrate the flexibility of the CAD method; experimental results show its validity for practical applications.