Cristiano Tomassoni

A New Class of Waveguide Dual-Mode Filters Using TM and Nonresonating Modes

An innovative class of very compact and selective waveguide dual-mode filters is presented in this paper. The basic structure is the TM dual-mode cavity. Such a cavity employs both resonant and nonresonating modes so as to provide two reflection and two transmission zeros. The high design flexibility in terms of transmission zero positioning and response bandwidth has been demonstrated by means of several single cavity designs. The design of Nth-order multiple cavity filters with N transmission zeros is presented and discussed. Different filter topologies are obtained depending on the waveguide structure used to connect adjacent cavities. An efficient mode-matching analysis method is proposed and verified for fast filter optimization. An eighth-order filter with eight transmission zeros has been designed, manufactured, and tested to demonstrate the potentialities of the filter class proposed.

Generalized TM Dual-Mode Cavity Filters

A new cavity arrangement, namely, the generalized TM dual-mode cavity, is presented in this paper. In contrast with the previous contributions on TM dual-mode filters, the generalized TM dual-mode cavity allows the realization of both symmetric and asymmetric filtering functions, simultaneously exploiting the maximum number of finite frequency transmission zeros. The high design flexibility in terms of number and position of transmission zeros is obtained by exciting and exploiting a set of nonresonating modes. Five structure parameters are used to fully control its equivalent transversal topology. The relationship between structure parameters and filtering function realized is extensively discussed. The design of multiple cavity filters is presented along with the experimental results of a sixth-order filter having six asymmetrically located transmission zeros.

Modal analysis of discontinuities between elliptical waveguides

Elliptical waveguides are currently finding applications in several components as corrugated horns, cavities for dual-mode filters and feeds for reflector antennas since they provide improved flexibility, better manufacturability, and higher Q with respect to either circular or rectangular waveguides. Efficient computer-aided design of components involving elliptical waveguides requires rapid evaluation of the scattering parameters at the discontinuities. To this end, we derive analytical formulas for full-wave study of a general junction between two elliptical waveguides and the relative specialization to the case of a junction between a circular and concentrical elliptical waveguide of larger cross section. With respect to current approaches, which are generally based on the numerical evaluation of the coupling integrals, the proposed analytical formulas allow to achieve a significant reduction of computer time. Results have been tested against published data and have also been compared with data obtained by numerical evaluation of the coupling integrals; in all cases, an almost perfect agreement has been observed.

A New Class of Pseudoelliptic Waveguide Filters Using Dual-Post Resonators

A new class of inline pseudoelliptic waveguide filters is presented in this paper. The proposed structure is based on a novel resonator, namely, the dual-post resonator, consisting of a pair of antipodal partial-height posts. The odd and even symmetry modes of the dual-post resonator are exploited as the resonant mode and nonresonating mode, respectively. The nonresonating mode generates a direct input-to-output coupling, thus providing a transmission zero that can be located either below or above the pole of the resonant mode. The coupling between the resonant mode and the source (or load), as well as the input-to-output coupling, can be controlled by properly selecting the height and position of each post of the dual-post resonator, no additional waveguide discontinuity being needed. N th-order filtering functions with a number of transmission zeros up to the number of poles can be realized by cascading N dual-post resonators. With respect to the conventional inline waveguide filter with inductive obstacles, the dual-post filter is easier to tune, shorter, and more selective, such advantages being paid by a somewhat lower Q factor. The design of fourth- and sixth-order dual-post filters is presented; the experimental results demonstrate the feasibility of the approach proposed.

Generalized Network Formulation: Application to Flange—Mounted Radiating Waveguides

Electromagnetic linear field problems can be rigorously and systematically formulated in terms of linear networks. Use of the equivalence theorem permits the decomposition of the computational domain into sub-domains with common interfaces. In each sub-domain the basic building blocks for a linear network representation are provided by Tellegens theorem and by the two alternative representations of the Greens function. Tellegens theorem provides the basis for expressing field at interfaces in a consistent way. The eigenfunction expansion of the Greens function provides a resonant-type equivalent circuit useful for expressing the field inside a sub-domain; while the Greens function direct solution emphasizes a transmission line network; in particular a spherical transmission line provides the network representation of radiation problems. In this paper, the generalized network formulation is applied to the problem of radiation from flange-mounted waveguides. While this problem has been already solved with a variety of approaches, the advantage of the generalized network formulation is that, while comprising the previously developed approaches, it also allows rigorous derivation of network representations. In particular it is shown that, by expressing the field in the half-space in terms of spherical waves, the physically matched solutions provide, in some cases, advantages for numerical computations and for network representations.

A new termination condition for the application of the TLM method to discontinuity problems in closed homogeneous waveguide

In this paper, we propose exact transmission-line matrix (TLM) boundary conditions for closed homogeneous waveguides. This approach is based on applying mode matching at the absorbing boundaries to the time-domain TLM algorithm. The absorbing condition in the time domain is achieved by the convolution of the modal characteristic impedances following inverse Fourier transform. The method is demonstrated for thick inductive irises in rectangular waveguide, showing excellent wide-band match of the fundamental mode, as well as of higher order modes excited by the discontinuity.

Quarter-Mode Cavity Filters in Substrate Integrated Waveguide Technology

This paper presents a systematic investigation of quarter-mode filters in substrate integrated waveguide (SIW) technology. This class of filters is particularly convenient because it combines the features of SIW structures with the improvement of size reduction. After a thorough analysis of the quarter-mode SIW cavity, this paper presents different coupling mechanisms and feeding techniques for the design of quarter-mode SIW filters: side coupling and corner coupling are considered, highlighting the advantages and disadvantages of the two techniques. Novel filter topologies are introduced, with the design and experimental verification of simple filters and their extension to higher order filter structures. Techniques to introduce transmission zeros are described and demonstrated. Moreover, the combination of quarter-mode SIW cavities and coplanar waveguide resonators leads to increasing the filter order to higher order and allows the implementation of quasi-elliptic filters.

Computer-aided design of in-line resonator filters with multiple elliptical apertures

A CAD procedure for a new type of in-line resonator filters with multiple elliptical-apertures irises is presented. The proposed design procedure, based on the concept of automated CAD of coupled resonator filters, considerably simplifies filter design since, with this approach, the choice of the initial geometrical dimensions is not critical. To increase the computational efficiency, at first optimization is carried out by using multivariate surrogate models derived from full wave analysis; final dimensions are then directly obtained by a rigorous full-wave optimization of the entire structure. Two examples of filters with two transmission zeros at lower and upper stop-band are presented in order to illustrate the approach.

Waveguide Component Analysis by a Generalized Network Approach

Efficient field computations for complex waveguide components require partitioning of the overall spatial domain into subdomains which are analyzed via suitable analytical or numerical methods and which are interconnected by field matching across the subdomain interfaces. Problem-matched alternative representations of the dyadic Greens functions for each subdomain permit derivation of corresponding alternative generalized networks. The algorithm architecture is presented in terms of a compact operator format that highlights the underlying principles. Simple examples of waveguide circuits are introduced in order to illustrate relevant concepts.

A parallel framework for the analysis of metal-flanged rectangular-aperture arrays

Computer-aided design of horn arrays, even by using state-of-the-art electromagnetic (EM) formulations, requires a considerable numerical effort and is, therefore, an ideal candidate for parallelization. We introduce a rigorous methodology, based on Petri nets and recursive bisection, in order to migrate a standard integral equation code toward parallel multiprocessor machines, following a data-flow design and a multiple-level parallelism. Significant (quasi-linear) speed-ups are demonstrated.