Jan Ritter

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.

3D subgrid technique for the finite difference method in the frequency domain

A new, efficient finite difference frequency domain (FD-FD) subgrid technique is introduced. Based on a robust direct orthogonalization of the FD-FD grid, the method does not require any additional interpolation or correction terms. This yields a significant reduction in both CPU time and storage requirements as compared with the usual graded mesh techniques. The rigorous S-parameter calculation of 3D dielectric or metallic post element examples in rectangular waveguides demonstrates the versatility of the method. Comparisons with measurements and calculated reference values verify the presented technique and show its high dynamic range.

A generalized 3D subgrid technique for the finite-difference time domain method

A new subgridding technique for finite difference (FD) methods is presented. The method is based on the integral form of Maxwells equations combined with a simple yet efficient orthogonalization technique for the discretization geometry at subgrid interfaces. No additional correction factors or interpolations are required. This leads to spurious-mode free solutions when applied to FD approximations of eigenvalue problems and to stable difference formulations when applied to the finite difference time-domain (FD-TD) method. The high efficiency of the subgridding technique is demonstrated by the FD-TD analysis of an inter-digital filter with circular posts.

Accelerated Simulation of Low Frequency Applications using Protheus/MLFMA

In order to extend the applicability of integral equation based methods to the analysis of complex structures at lower frequencies, an efficient formulation of the low frequency fast inhomogeneous plane wave algorithm has been implemented in the Protheus/MLFMA simulation tool. The seamless integration of the new low frequency method with the well known multilevel fast multipole algorithm within Protheus/MLFMA delivers a method capable of efficient accelerated wideband analysis for a large range of applications such as integration of communication antennas on ships, design of wideband antennas and EMC tasks.

Locally conformed subgrid FD-FD technique for the analysis of 3D waveguide structures with curved metallic objects

A conformed subgrid finite-difference frequency domain (CS FD-FD) algorithm is presented. The method combines the advantages of both a locally conformed grid for modeling curved perfectly conducting bodies and a direct orthogonalization subgrid technique for regions of high field intensity. This reduces significantly CPU time and storage requirements. The usefulness of the method is demonstrated for a metallic post structure in a rectangular waveguide and a dielectric resonator filter including coaxial coupling elements. The method is verified by reference values.

A wide-band S-parameter extraction procedure for arbitarily shaped, inhomogeneous structures using time domain numerical techniques

A new, simple and very efficient technique for the wide-band extraction of scattering parameters using time domain methods (e.g. FDTD, TLM) is introduced which avoids the hitherto necessary high requirements for appropriate absorbing boundary conditions. The technique is based on the modal S-parameter definition for unmatched ports and achieves, even with standard non-dispersive Murs absorbing boundaries, excellent and reliable results also for dispersive microwave structures and inhomogeneous input and output ports. The proposed method is verified by excellent agreement with measurements or with mode-matching results.<<ETX>>

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.

FD-TD/matrix-pencil method for the efficient simulation of waveguide components including structures of more general shape

A combined FD-TD/matrix-pencil method is introduced for the efficient and rigorous calculation of the full-wave modal S-parameters of waveguide components including structures of more general shape or of high complexity. The application of the S-parameter definition for unmatched ports requires merely standard Murs absorbing boundaries for reliable results, and a nonorthogonal or contour path mesh formulation allows the convenient inclusion of curved boundaries. The efficiency of the method is demonstrated at the analysis of waveguide components of practical importance, such as the twisted waveguide, the twisted waveguide bend, and the waffle-iron filter. The proposed method is verified by excellent agreement with FEM/mode-matching results.

Mode Stirring Chambers for full size aircraft tests: concept- and design-studies

Mode Stirring Chambers (MSCs) provide an interesting environment for testing electronic systems against radiated electromagnetic fields. As the MSC method is discussed controversy these days, the MSC test procedure offers advantages compared to conventional approaches (outdoor ranges, anechoic chambers). The most interesting aspects are time effective testing as well as lower equipment costs (amplifiers, antennas, facilities) due to reduced power requirements and the absence of absorbers. These aspects render MSCs especially interesting for the test of large objects, like aircrafts (A/C) of the size of a Eurofighter Typhoon. Besides the aforementioned advantages, the MSC method also pose some drawbacks, namely, the loss of input-angle dependent information, the influence of losses in the DUT on the required excitation power levels, and finally, MSC testing is still not yet approved by military authorities. From this starting point in 2001, EADS Military Aircraft initiated a series of studies for the evaluation and planning of a MSC for full size aircraft testing. In the first part of this contribution, the general concept is outlined and some relevant parameters are given. In the second part, the subject of the evaluation of different mode-tuners by means of numerical simulations is addressed.

Advanced FD-TD Techniques for the CAD of 3D Microwave Components

Advanced techniques for the finite difference time domain (FD-TD) method are described, which improve the efficiency of the simulation of three-dimensional (3D) microwave components, including structures of more general shape. The formulations are based on a combination of a direct subgrid technique with a locally conformal FD-TD algorithm for arbitrarily shaped perfect conductors, and with a modified intersection approach for arbitrary dielectric boundaries. The involved subgrid technique, where a main grid is directly orthogonalized against a dual grid, avoids the usual necessity of additional interpolation terms. Application of the matrix pencil method reduces the number of required time steps. Advantages of the combined techniques are high accuracy, flexibility, and efficiency concerning both storage capacity and CPU time. Their versatility for the CAD of 3D microwave structures is demonstrated with typical examples, like coax feed with dielectric coating, dielectric resonator filter, and waffle-iron filter with round teeth. The accuracy is verified by available measurements or reference calculations.