V. Catina

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.

Hybrid surface integral-equation/mode-matching method for the analysis of dielectric loaded waveguide filters of arbitrary shape

A surface integral-equation method is combined with the mode-matching technique for the rigorous efficient analysis of waveguide filters containing arbitrarily shaped dielectric posts in arbitrary waveguide housings. The advantage of the proposed method against existing approaches is its high flexibility for calculating structures being not restricted by specific canonical shapes. A locally refined adaptive triangular surface mesh, together with the application of Rao-Wilton-Glisson and aperture eigenfunctions, respectively, for basis functions, achieves reliable modeling. The accuracy of the presented method 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.

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.

Rigorous surface integral method-of-moment analysis of rectangular waveguide edge-slot arrays

This paper presents a surface integral method for the rigorous analysis of edge-slot arrays of finite extension. The free space Greens function provides the desired flexibility. The numerical solution by the method-of-moments (MoM) allows the convenient calculation of the antenna pattern and of the generalized admittance matrix at the waveguide ports including higher-order modes for the intended further combination with fast hybrid mode-matching/finite-element (MM/FE) building blocks. The flexibility and accuracy of the method is verified by available reference results and 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.

Efficient surface integral equation analysis of aperture antennas with radomes

For protecting antennas from environmental effects, and preserving aerodynamic profiles of objects with antennas, dielectric radomes are used already for a long time [1]. The presence of radomes, which commonly have different shapes, cf. e.g. [2], can significantly affect the radiation characteristics of corresponding antennas, and, hence, their analysis has found much attention in the recent past. For aperture antennas with radomes, cf. schematic sketch in Fig. 1 [3], many different techniques have been applied so far, such as ray optics [4], equivalence principles with image theory [5], integral equation (IE) methods for 2D problems [6], hybrid physical optics-method of moments (PO-MoM) techniques [3], and the finite-difference time-domain (FD-TD) method [7]. Approximate methods can lead to accuracy problems, 3D solvers can be too time consuming for desirable optimizations.

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.

Fast method of moments analysis of a class of dielectric loaded horns applying higher-order vector basis functions

Dielectric loaded horns have found widespread application due to their inherent potential of having features similar to corrugated horns, while being less frequency sensitive and more easily to be manufactured, in particular for higher frequencies. In this paper, we follow a different MoM approach by using divergence-conforming higher-order vector basis functions, which have mostly been employed for scattering and microstrip antenna problems so far. Moreover, curved surfaces is modeled using curvilinear triangles in order to minimize geometrical modeling inaccuracies. The advantages include higher efficiency, accuracy and flexibility. For solving the given problem, the electric field integral equation (EFIE) is combined with the Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) formulation. The combined formulation is named EFIE-PMCHWT method underlining the fact that the EFIE is applied to model the fields on the aperture and conductor surfaces, and the PMCHWT method is utilized for modelling dielectric structures inside the waveguide housing.

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